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outbreak investigation - types of epidemics and investigating them

This document discusses an upcoming presentation on outbreak investigation. It begins with definitions of key terms like epidemic, outbreak, endemic, and pandemic. It then discusses determinants of disease outbreaks and types of epidemics. The objectives, steps, and examples of outbreak investigation are provided. Various factors related to outbreaks like incubation period, quarantine, herd immunity, and triggers for surveillance are defined.

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Presented by: Dr. Timiresh Kumar Das Moderator: Dr. Neelam Roy Associate Professor Dept. of Community Medicine VMMC & Safdarjung Hospital
 Definitions  Determinants of disease outbreaks  Types of epidemics  Objectives of investigation of outbreak/ epidemic  Steps of outbreak investigation  Some examples  References
 Epidemic: [Greek: epi (upon) demos (the people)]  The occurrence in a community or region of cases of an illness, specific health related behaviour, or other health related events clearly in excess of normal expectancy.1 A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  The “unusual” occurrence in a community or region of disease, specific health related behaviour, or other health related events clearly in excess of “expected occurrences”.2 Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010  The occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy, and derived from a common or from a propagated source.3 Epidemiology – 4th ed; Gordis L. 2004
 Outbreak:  An epidemic limited to a localised increase in the incidence of a disease, e.g., in a village, town, or closed institution. (= upsurge)1 A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  A term used for a small, usually localised epidemic in the interest of minimising public alarm.2 Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010  An outbreak is the occurrence of illness, specific health related behaviour, or other event clearly in excess of normal expectancy in a community in a specified time period. An outbreak is limited or localised to a village, town, or closed institution.4 Checklist for CRRT for outbreak investigation, NICD 2008
 According to the Oxford Textbook of Public Health the criteria for judging that an outbreak has happened can be one of the following.5  The occurrence of a greater number of cases or events than normally occur in the same place when compared to the same duration in past years.   A cluster of cases of the same disease occurs which can be linked to the same exposure.   E.g. Kaposi's sarcoma, New York - 30 in 1981; only 2-3 previous yrs. E.g. 3 athletes admitted with acute febrile illness after triathlon in Springfield, Illinois. Triathlon related to illness. Leptospira. A single case of disease that has never occurred before or might have a significant implication for public health policy and practice can be judged an outbreak which deserves to be investigated.  E.g. - Avian flu (H5N1) Hong Kong in a 3-year boy in May 1997 alerted local auth. and scientists around the world to start a full-scale investigation.
 Endemic: The constant presence of a disease or infectious agent within a given geographic area or population group, without importation from outside; may also refer to the usual or expected frequency of the disease within such area or population group. A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  Pandemic: An epidemic usually affecting a large proportion of the population, occurring over a wide geographic area such as a section of a nation, the entire nation, or a continent or the world. A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.
SUSCEPTIBLE DISEASE OUTBREAK IMMUNE NO OUTBREAK  When formerly isolated populations are exposed to disease. 19th century – measles in Faroe islands.  When susceptible population is introduced to an endemic area – streptococcal sore throat outbreaks when new recruits arrived at Great Lakes Naval Station, USA.
 Herd Immunity: The immunity o f a group or community. The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of the individuals members of the group.1  When a large proportion of the population is immune, the entire population is likely to be protected, not only those who are immune.  Degree depends on – Extent of random mixing of the population  Agent and transmission characteristics.  Environmental factors.  Number of susceptibles and immunes in the population. 
14 12 10 8 Expected number of cases if effect limited to vaccines 6 REDUCED BY HERD IMMUNITY Number of cases observed 4 2 0 1958 1959 1960 1961
 Incubation Period: Interval from receipt of infection to the time of onset of clinical illness.1 Important in case of isolating infected people to prevent transmission.  Isolation or quarantine should be greater than maximum incubation period.  Useful if disease may be introduced into new areas. 
 Quarantine: The restriction of activities of well persons or animals who have been exposed to a case of communicable disease during its period of communicability (i.e. contacts) to prevent disease transmission during incubation period if infection should occur.1 From quarante giorni (40 days).  Plague (Black Death) Europe, 1374 – Venetian Republic  1377, Ragusa detained travellers in an isolated area, initially for 30 days and, when it did not work, for 40 days 
 Common-source epidemics  Single source or point source epidemics  Continuous or multiple exposure epidemics  Propagated epidemics  Person to person  Arthropod vector  Animal reservoir  Slow (modern) epidemics
 Point Source: A point source outbreak occurs when there is one single source that exists for a very short time and all cases have common exposure to it in that same particular period.  Ex: food poisoning
 Common source single exposure First case and the last case happen within one incubation period  Rapid rise in number of cases followed by rapid decline   Example:  Food poisoning due to spoiled food item in a feast.  Bhopal gas tragedy ( 198
 Common source multiple exposure: There is only one source, which provides continuous or intermittent exposure over a longer period  Example:  Prostitute transmitting STD to her clients  Typhoid Mary  Water supply contamination due to leaky pipes.  Continuous if leak is constant.  Intermittent if leak occurs during pressure variations.
 Propagated epidemic: This kind of outbreak is caused by a transmission from one person to another person.  Example: SARS, H1N1 influenza
To define the magnitude  To determine the particular conditions and factors responsible for the occurrence of the epidemic  To identify the cause, source of infection, and modes of transmission  To formulate prevention and control measures 
       To control the current outbreak. Prevention of future outbreaks. Describe new diseases and learn more about known diseases. Evaluation of the effectiveness of prevention programmes. Evaluation of the effectiveness of the existing surveillance system. Training health professionals. Responding to public, political, or legal concern .
 The first person who comes across news of an outbreak / The health worker/ ANM  PHC medical officer / the CHC in charge  The District health officer / District RRT or DEIT/ State RRT  Specialized agencies like NCDC (NICD).
1. Verification of the diagnosis 2. Confirmation of existence of outbreak 3. Defining population at risk – Map, Count 4. Rapid search for cases and characteristics 5. Data Analysis – Time, Place, Person 6. Formulation of hypothesis 7. Testing of hypothesis 8. Evaluation of ecological factors 9. Further investigations 10. Reporting
 Verify rumours  Technical, Administrative and Logistics arrangement  Prepare Outbreak Management Kit according to initial information  Brief members of the investigating team regarding Roles & responsibilities  Methods of personal protection  Team composed of: 1. Nodal officer (Epi/ PHS) 2. Clinician 3. Microbiologist 4. Health Assistant 5. District/ Local administration nominee 6. Other personnel as required
 Verification of the diagnosis is usually made on clinical and laboratory parameters.  Ensure that the problem has been properly diagnosed -- the outbreak really is what it has been reported to be  Review clinical findings and laboratory results for affected people  Visit or talk to several of the people who became ill For outbreaks involving infectious or toxic chemical agents, be certain that the increase in diagnosed cases is not the result of a mistake in the laboratory.
 Incidence rate is calculated by dividing the total cases by the population at risk. 7 ye ar ave rage incide nce vs . 2003 incide nce of D e ngue in 2003 D e lhi av g 2000 1861 1800 1600 1400 n o . o f c as e s  This rate is compared with the rate occurring in the same population, during the corresponding period of the previous years. 1200 1189 1000 800 600 600 0 200 0 0 400 0 0 0 0 0 1 0 0 0 F M A M J 10 4 J 213 2 1 0 J 15 362 A months of reporting 148 101 S O N D
• • • • • Clustering of cases or deaths Increases in cases or deaths Single case of disease of epidemic potential Acute febrile illness of an unknown etiology Two or more linked cases of disease with outbreak potential(e.g., Measles, Cholera, Dengue, Japanese encephalitis or plague) • • • • • • Unusual isolate (Cholera O 139) Unusual presentation Environmental factors e.g. rainfall, climate Shift in age distribution of cases High vector density Natural disasters
 Rumour register  To be kept in standardized format in each institution  Community informants  Private and public sector  Media  Important source of information, not to neglect  Review of routine data – surveillance data  Triggers (There are triggers for each condition under surveillance, Various trigger levels may lead to local or broader response)
 Threshold for diseases under surveillance that trigger pre- determined actions at various levels  Based upon the number of cases in weekly report  Trigger levels depend on:  Type of disease  Case fatality (Death / case ratio)  Number of evolving cases  Usual trend in the region
Trigger Significance Levels of response 1 Suspected /limited outbreak • Local response by health worker and medical officer 2 Outbreak • Local and district response by district surveillance officer and rapid response team 3 Confirmed outbreak • Local, district and state 4 Wide spread epidemic • State level response 5 Disaster response • Local, district, state and centre
 Examples:  Trigger levels for Dengue  Trigger 1 • Clustering of 2 similar case of probable Dengue fever in a village • Single case of Dengue hemorrhagic fever  Trigger 2 • More than 4 cases of Dengue fever in a village 1000 population.  Triggers for syndromic surveillance  Fever • More than 2 similar case in the village (1000 Population)  Jaundice • More than two cases of jaundice in different houses irrespective of age in a village or 1000 population
Disease alerts/ outbreaks reported and responded to by states/ UTs through IDSP; 2nd week (ending 15th January, 2012)
• Severity of illness • Number of cases • Source / mode of transmission • Availability of preventive & control measures • Availability of staff & resources • Public, political and legal concerns • Public health program considerations •Potential to affect others if the control measures are not taken • Research opportunity
 Pseudo-outbreaks:  Artifact in the numerator:  Increased awareness  Reporting of prevalent cases as incident cases (e.g.; hepatitis C, sleeping sickness)  Laboratory error  Variation of the denominator:  Rapidly changing population denominators  Migrants or refugees
 Obtain a map of the area  Counting of the population  Helps to calculate the denominator for further calculation of attack rates.  Provides us with the possible number of people at risk.  Mapping helps us to know area: ecological and environmental factors.
 Map : Detailed, Current map of the area.  If not available – prepare  Information: Natural landmarks, Roads, All dwelling units, Sources of water, Other important features   Counting: Census by age and sex  Lay health workers  House to house visits 
 Includes: Framing a case definition, searching for cases and doing a epidemiological survey.  A case definition is a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest.  Criteria     Clinical and/or biological criteria, Time Place Person  Case definition should be balanced, practical, reliable and applied without bias.
Example - Measles: 3 definitions  Fever and runny nose  Too sensitive  Too many other illnesses produce same symptoms  Call many illnesses “measles”  Fever and rash and Koplik’s spots and conjunctivitis  Too specific  Many cases of measles do not have all these signs  Miss many real cases of measles  IDSP case definition: Fever of 3-7 days duration, with generalized maculopapular rashes; with history of cough, coryza, conjunctivitis or Koplik’s spots.
 Suspect -Fewer of the typical clinical features  Probable- Typical clinical features of the disease without laboratory confirmation.  Confirmed- Typical clinical features with laboratory verification. Confirmed Case Laboratory Verification ++ Possible Case + Clinical Features Probable Case ++ +
 Example: E. coli O157 outbreak at Restaurant X on 31/3/2010  Possible: diarrhea (3 loose stools per day) and ate food purchased at restaurant X on 31/3  Probable: bloody diarrhea and ate food purchased at restaurant X during on 31/3  Confirmed: culture positive with “outbreak” PFGE pattern and ate food purchased from restaurant X on 31/3
 Case Definition may need to be updated within an investigation  Broad to specific  Infection with E. coli O157 vs. infection with the outbreak strain (defined by PFGE pattern)  Location of exposure  SARS outbreak (travel within 10 d of onset): • In February: China/HK/Hanoi/Singapore • In April: Toronto, Canada added • In May: Taiwan added  Dates of exposure can change  SARS outbreak: to meet the case definition-dates of exposure dependant on location of exposure
 The first cases to be recognized are usually only a small proportion of the total number  To identify other cases, use as many sources possible  Passive Surveillance - Relies on routine notifications by healthcare personnel  Active Surveillance - Involves regular outreach to potential reporters to stimulate reporting of specific conditions; investigators are sent to the afflicted area to collect more information  Contact physician offices, hospitals, schools to find persons with similar symptoms or illnesses  Send out a letter, telephone or visit the facilities to collect information  Through media alerts asking people to get checked
WHY TO SEARCH Iceberg phenomenon 40
 The information is collected by “line listing”.  A line list is like a nominal roll of the cases being reported to the various health care establishments (like dispensaries, general practitioners or admitted to the hospitals)  Constitutes and updates a database of cases  Done by hand or by Excel.
 The survey team will go for “door to door” survey in the affected area and ask if any person had suffered with symptoms fitting into case definition (Rapid Household Survey)  If yes, their details were recorded on the epidemiological case - sheet and required samples are taken and dispatched to the hospital/ reference laboratory. Epidemiological case sheet = Case interview form  Detailed information from the case relevant to the disease under study. 
Information includes: • Name, Age, Sex, Occupation, Social class • Time of onset of disease, Signs & Symptoms • Personal contact at home, work, school • Travel history, attendance at large gatherings • History of previous exposure/injections, • Special events such as parties attended, foods eaten, and exposure to common vehicles such as water, food and milk
 Active door-to-door collection of information is by “ Rapid Household Survey”
 Characterizing an outbreak by time, place and person is called descriptive epidemiology.  Descriptive epidemiology is important because:  What is reliable and informative (e.g., similar exposures)  What may not be as reliable (e.g., many missing responses to a particular question)  Provides a comprehensive description of an outbreak by showing its trend over time, its geographic extent (place) and the populations (people) affected by the disease
 Development of proportional distribution of cases according to host characteristics (age, race, sex) or by exposures (occupation, leisure activities, use of medications, tobacco, drugs).
 Count  Count the cases in each age and sex groups  Divide  Obtain census denominators for each age and sex groups  Compare  Estimate the incidence for each:  Age group  Sex group
 An attack rate is the proportion of a well-defined population that develops illness over a limited period of time, such as during an epidemic or outbreak  What are the age and gender specific attack rates?  What age and gender groups are at highest and lowest risk of illness?  In what other ways do the characteristics of the cases differ significantly from those of the general population? Purpose => Identification of sub-group(s) at risk
Attack rate of measles by age and sex, Cuddalore, Tamil Nadu, India, 2004-2005 Characteristics Age group Number of Population cases Attack rate per 100,000 255,755 19.6 51 1,795,383 2.8 Male 48 1,032,938 4.6 Female Total 50 5+ Sex 0-4 53 1,018,200 5.2 101 2,051,138 4.9
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Protestants Coptic Christians Muslims Population Cases of Botulism BOTULISM OUTBREAK IN CAIRO, EGYPT - APRIL1993 Weber JT, Hibbs RG Jr, Darwish A, et al. A massive outbreak of type E botulism associated with traditional salted fish in Cairo. J Infect Dis 1993; 167: 451-454
What is the exact period of the outbreak? What is the probable period of exposure? Is the outbreak likely common source or propagated?
Drawing the epidemic curve based on time distribution of cases 2. Eyeball distribution to choose interval 1. Count cases by time of onset 3. Finalize
 Interpretation of epidemic curve Shape – type of epidemic  An early case in the curve may represent source of the epidemic  Give information about the time course of an epidemic and what the future course might be  In a point-source epidemic of a known disease with a known incubation period, epidemic curve provides information to identify a likely period of exposure  Shape of epidemic curve illustrates type of epidemic. 
Mean incubation period
Common source single exposure:  Sharp increase followed by a rapid decline.
Continuous common source outbreak:  An abrupt increase in the number of cases but, new cases persist for a longer time with a plateau shape instead of a peak before decreasing.
• Intermittent common source: multiple peaks
 Propagated source outbreak: Number of cases  Increase in the number of cases with progressive peaks 16 14 12 10 8 6 4 2 0 1 4 7 10 13 16 19 22 25 28 31 34 Date
 The spatial relationships of cases are shown best on a spot map.  A spot map showing the location of cases can give an idea of the source of infection like maps show that the cases occurred in proximity to a body of water, a sewage treatment plant, or its outflow. DRAWING A ROUGH SPOT MAP
 Questions to be asked and answered:  What is the most significant geographic distribution of cases?  Place of residence? Workplace?  Do the attack rates vary by place?  Relation to any landmark or possible source?
 Usually we generate hypotheses from the beginning of the outbreak, however, at this point, the hypotheses are sharpened and more accurately focused.  To consider what is known about the disease itself: What is the agent’s usual reservoir? B. How is it usually transmitted? C. What vehicles are commonly implicated? D. What are the known risk factors? A.
 Talk to people who are ill: In-depth open interviews, Group discussions  Hypotheses should be proposed in a way that they can be tested.
 After a hypothesis is formulated, one should be able to show that:  all additional cases, lab data, and epidemiologic evidence are consistent with the initial hypothesis  no other hypothesis fits the data as well  Observations that add weight to validity:  The greater the degree of exposure (or higher dosage of the pathogen), the higher the incidence of disease  Higher incidence of disease in the presence of one risk factor relative to other factors
 Approaches:  Comparison of hypothesis with known/ established facts.  Analytic epidemiology to test the hypothesis  First method is used when the evidence is so strong that hypothesis need not be tested  Example - A 1991 investigation of an outbreak of vitamin D intoxication in Massachusetts. All affected drank milk from local dairy. Hypothesis - dairy was source, milk vehicle of excess vit D. Visit to dairy, they quickly recognized that far more than the recommended dose of vitamin D was inadvertently being adding to the milk. No further analysis was necessary.
 Analytic epidemiology is used when cause is less clear. Cohort studies  Case control studies   What to use? Case control Rare disease/ large community Common disease/ small community Complete population accessible Large amount of resources Limited resources Cohort +++ - - +++ +/- +++ + ++ +++ -
Example: Case control study for an outbreak of Acute Gastroenteritis following a dinner. FOOD ATE and ILL N (%) ATE and NOT ILL N (%) ODDS RATIO TOMATOES 14 (82) 30 (86) 0.83 CHICKEN 13 (71) 34 (94) 0.11 ALFAALFA SPROUTS 10 (67) 6 (17) 8.25
 These are additional studies undertaken to corroborate the findings of the epidemiological study.  Environmental studies  Microbiological studies  Entomological studies
 Environmental studies often help explain why an outbreak occurred and may be very important in certain settings.  Example: Site of contamination of irrigation canal with cattle urine in an outbreak of Leptospirosis in southeastern Washington, August 1964. Pond connected to irrigation canal And Cattle around the site
 Microbiological studies can clinch the relationship between suspected source and outbreak.  Example: In the above outbreak of Leptospirosis, culture of urine from the cattle, water of the canal and blood of affected children yielded the same strain of L. pomona. Also, the children who had recovered showed increased anti leptospiral antibodies.
 Entomological studies help identify the vector responsible for the outbreak.  May also give useful insight into the life cycle of the pathogen and the mode of transmission Example: Vector surveillance in Chikungunya affected villages of Latur and Beed districts of Maharashtra, 2006
 Additional epidemiologic studies  What questions remain unanswered about the disease?  What kind of study used in a particular setting would answer these questions?  When analytic studies do not confirm the hypotheses  reconsider the original hypotheses  look for new vehicles or modes of transmission  Additional investigations  Further lab studies  Refine hypothesis till confirmation
 Report provides a blueprint for action.  It also serves as a record of performance and a document for potential legal issues.  It serves as a reference if the health department encounters a similar situation in the future.  In public health literature serves the purpose of contributing to the knowledge base of epidemiology and public health  Daily interim reports and final report.
Contents of a Report: 1. Back ground 2. Historical data 3. Methodology of investigation 4. Analysis of data (clinical data, Epidemiological data, modes of transmission, Lab data, Interpretation of data) 5. Control measures 6. Evaluation 7. Preventive measures
Report to be submitted by investigating officer/ team to the next higher authority within one week of completion of investigations
 Appropriate control measures  based on Epidemiological, Clinical, Environmental findings  To prevent further spread of disease  The elements of epidemic control include: 1. Controlling the source of the pathogen (if known) Remove or inactivate the pathogen 2. Interrupting the transmission. Sterilize environmental source of spread; vector control 3. Modifying the host response to exposure. Immunization; Prophylactic chemotherapy
 Control measures should be implemented at the earliest.  DO NOT wait for laboratory confirmation to start control measures.
 Follow up of outbreak  Detect last case  Detect and treat late complications  Complete documentation  Evaluation of outbreak management including investigations (by local authorities) Genesis of outbreak  Early or late detection of outbreak  Preparedness for outbreak  Management of the outbreak  Control measures taken and their impact 
 Documentation and sharing the lessons learnt Post outbreak seminar.  Feedback to local health authorities, RRTs and other concerned.  Developing case studies on selected outbreaks for training purposes. 
Audience Medium Focus of the content Communication objective Epidemiologists, laboratory •Report •Epidemiology •Documentation of the source Public health managers •Summary •Recommendations •Action Political leaders •Briefing •Control measures •Evidence that the situation is under control Community •Press release, interview •Health education •Personal steps towards prevention Scientific community •Presentation, manuscript •Science •Scientific progress POSSIBLE MATRIX FOR COMMUNICATION OF INVESTIGATION RESULTS AND FINDINGS
 An outbreak of fever, URI & loose motion among the boarders of PTS, Jharoda kalan, Delhi was reported to the MS of SJH by CDMO of SW district of Delhi on 10.07.09 .  Cause for concern – Panic d/t novel H1N1 cases in Delhi  RRT composition – Epidemiologist, Physician, Microbiologist and other doctors. (11.07.09)  Case definition: A person with acute onset of fever with or without sore throat, diarrhea, headache, body ache starting from 2nd July 2009 onward.  Line listing, Epidemiological case sheet (with travel history), Lab analysis of samples for H1N1.
 Descriptive: Time – Start = 2nd Jul, Peak = 7th Jul, Fall afterwards  Place – Start in Tent # 40, 25 & 8; then spread. clustered around tent no 1,9,20, 22, 27, 36 &37.  Person – 61 cases. Mean age 22.2 yrs (20-49).   Environmental: Crowded, ill ventilated tents. Humid environment with low temperature.  Lab: H1N1 negative. Influenza A +ve.  Recommendations:    Reduce crowding, Improve ventilation Increase staffing in dispensary and Proper record maintainance Prompt identification and reporting of changes in disease frequency.
 Outbreak of jaundice among the residents of Sector 8 of RK Puram, New Delhi was reported to the MS of SJH by CDMO of SW district of Delhi on 06.04.2011.  Initial report by DSO suggested sudden onset of jaundice.  RRT – Epidemiologist, Physician, Microbiologist and other personnel. To CGHS, dispensary on 06.04.2011  Case defn : A person with signs and symptoms of jaundice with or without elevated serum aminotransferase levels from 1st January 2011 onwards  Verification of outbreak by review of records of CGHS dispensary.
 Rapid survey, Line listing, Spot map, Clinical examination, Epidemiological case sheet, Blood samples, Environmental study  Descriptive: Time – Rise from 15th Jan, Peak 1st week March, Decline afterwards. Max cases in March (11/21)  Place – Clustering around N block & adjacent to Palam rd  Person – 15-30 yrs (50%), M > F (58.3/ 41.7)   Lab: 3/5 recent cases +ve for Anti HEV IgM. 2/6 water samples – Fecal contamination
 Environmental: Water & sewer lines running close, Intermittent water supply – Booster pumps, Latrine near water storage tank, Sewer lines not de-silted – overflowing, Damaged water lines. Absent residual chlorine.  Conclusion: Confirmed outbreak of jaundice. Lab results  Acute Hepatitis E. Damaged water lines and contamination from sewer lines responsible.  Recommendations: Proper record maintenance in CGHS dispensary(diagnosis, S/s)  Monitoring and repairing of water lines  Sewer lines should not be close to water supply pipeline  Regular de-silting and cleaning of sewer line.  Proper chlorination of water supply. 
1. A Dictionary of Epidemiology – 3rd ed; Last JM. 2. 3. 4. 5. 6. 2000. Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010. Epidemiology – 4th ed; Gordis L. 2004. Checklist for CRRT for outbreak investigation, NICD 2008 Oxford Textbook of Public Health – 4th ed; 2002 Mausner & Bahn Epidemiology: An Introductory Text – 2nd ed; Mausner JS, Kramer S. 1985.
7. R Bonita, R Beaglehole, T Kjellström. Basic Epidemiology: WHO;2nd Edition. 8. Outbreak Investigations Around The World: Case Studies in Infectious Disease Field Epidemiology; Mark S Dworkin. 2010 9. Steps of outbreak investigation; Epidemiology in the classroom. Excite, CDC. From www.cdc.gov 10. Raut DK, Roy N, Nair D, Sharma R. Influenza A virus outbreak in Police Training School, Najafgarh, Delhi – 2009. Indian J Med Res; Dec 2010; 132: 731-732
LARGE OUTBREAKS FROM AROUND THE WORLD – WHO, 1999

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outbreak investigation - types of epidemics and investigating them

  • 1.
    Presented by: Dr.Timiresh Kumar Das Moderator: Dr. Neelam Roy Associate Professor Dept. of Community Medicine VMMC & Safdarjung Hospital
  • 2.
     Definitions  Determinantsof disease outbreaks  Types of epidemics  Objectives of investigation of outbreak/ epidemic  Steps of outbreak investigation  Some examples  References
  • 3.
     Epidemic: [Greek:epi (upon) demos (the people)]  The occurrence in a community or region of cases of an illness, specific health related behaviour, or other health related events clearly in excess of normal expectancy.1 A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  The “unusual” occurrence in a community or region of disease, specific health related behaviour, or other health related events clearly in excess of “expected occurrences”.2 Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010  The occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy, and derived from a common or from a propagated source.3 Epidemiology – 4th ed; Gordis L. 2004
  • 4.
     Outbreak:  An epidemiclimited to a localised increase in the incidence of a disease, e.g., in a village, town, or closed institution. (= upsurge)1 A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  A term used for a small, usually localised epidemic in the interest of minimising public alarm.2 Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010  An outbreak is the occurrence of illness, specific health related behaviour, or other event clearly in excess of normal expectancy in a community in a specified time period. An outbreak is limited or localised to a village, town, or closed institution.4 Checklist for CRRT for outbreak investigation, NICD 2008
  • 5.
     According tothe Oxford Textbook of Public Health the criteria for judging that an outbreak has happened can be one of the following.5  The occurrence of a greater number of cases or events than normally occur in the same place when compared to the same duration in past years.   A cluster of cases of the same disease occurs which can be linked to the same exposure.   E.g. Kaposi's sarcoma, New York - 30 in 1981; only 2-3 previous yrs. E.g. 3 athletes admitted with acute febrile illness after triathlon in Springfield, Illinois. Triathlon related to illness. Leptospira. A single case of disease that has never occurred before or might have a significant implication for public health policy and practice can be judged an outbreak which deserves to be investigated.  E.g. - Avian flu (H5N1) Hong Kong in a 3-year boy in May 1997 alerted local auth. and scientists around the world to start a full-scale investigation.
  • 6.
     Endemic: Theconstant presence of a disease or infectious agent within a given geographic area or population group, without importation from outside; may also refer to the usual or expected frequency of the disease within such area or population group. A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.  Pandemic: An epidemic usually affecting a large proportion of the population, occurring over a wide geographic area such as a section of a nation, the entire nation, or a continent or the world. A Dictionary of Epidemiology – 3rd ed; Last JM. 2000.
  • 7.
    SUSCEPTIBLE DISEASE OUTBREAK IMMUNE NO OUTBREAK  When formerlyisolated populations are exposed to disease. 19th century – measles in Faroe islands.  When susceptible population is introduced to an endemic area – streptococcal sore throat outbreaks when new recruits arrived at Great Lakes Naval Station, USA.
  • 8.
     Herd Immunity:The immunity o f a group or community. The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of the individuals members of the group.1  When a large proportion of the population is immune, the entire population is likely to be protected, not only those who are immune.  Degree depends on – Extent of random mixing of the population  Agent and transmission characteristics.  Environmental factors.  Number of susceptibles and immunes in the population. 
  • 9.
    14 12 10 8 Expected number ofcases if effect limited to vaccines 6 REDUCED BY HERD IMMUNITY Number of cases observed 4 2 0 1958 1959 1960 1961
  • 10.
     Incubation Period:Interval from receipt of infection to the time of onset of clinical illness.1 Important in case of isolating infected people to prevent transmission.  Isolation or quarantine should be greater than maximum incubation period.  Useful if disease may be introduced into new areas. 
  • 11.
     Quarantine: Therestriction of activities of well persons or animals who have been exposed to a case of communicable disease during its period of communicability (i.e. contacts) to prevent disease transmission during incubation period if infection should occur.1 From quarante giorni (40 days).  Plague (Black Death) Europe, 1374 – Venetian Republic  1377, Ragusa detained travellers in an isolated area, initially for 30 days and, when it did not work, for 40 days 
  • 12.
     Common-source epidemics Single source or point source epidemics  Continuous or multiple exposure epidemics  Propagated epidemics  Person to person  Arthropod vector  Animal reservoir  Slow (modern) epidemics
  • 13.
     Point Source:A point source outbreak occurs when there is one single source that exists for a very short time and all cases have common exposure to it in that same particular period.  Ex: food poisoning
  • 14.
     Common sourcesingle exposure First case and the last case happen within one incubation period  Rapid rise in number of cases followed by rapid decline   Example:  Food poisoning due to spoiled food item in a feast.  Bhopal gas tragedy ( 198
  • 15.
     Common sourcemultiple exposure: There is only one source, which provides continuous or intermittent exposure over a longer period  Example:  Prostitute transmitting STD to her clients  Typhoid Mary  Water supply contamination due to leaky pipes.  Continuous if leak is constant.  Intermittent if leak occurs during pressure variations.
  • 16.
     Propagated epidemic:This kind of outbreak is caused by a transmission from one person to another person.  Example: SARS, H1N1 influenza
  • 17.
    To define themagnitude  To determine the particular conditions and factors responsible for the occurrence of the epidemic  To identify the cause, source of infection, and modes of transmission  To formulate prevention and control measures 
  • 18.
           To control thecurrent outbreak. Prevention of future outbreaks. Describe new diseases and learn more about known diseases. Evaluation of the effectiveness of prevention programmes. Evaluation of the effectiveness of the existing surveillance system. Training health professionals. Responding to public, political, or legal concern .
  • 19.
     The firstperson who comes across news of an outbreak / The health worker/ ANM  PHC medical officer / the CHC in charge  The District health officer / District RRT or DEIT/ State RRT  Specialized agencies like NCDC (NICD).
  • 20.
    1. Verification ofthe diagnosis 2. Confirmation of existence of outbreak 3. Defining population at risk – Map, Count 4. Rapid search for cases and characteristics 5. Data Analysis – Time, Place, Person 6. Formulation of hypothesis 7. Testing of hypothesis 8. Evaluation of ecological factors 9. Further investigations 10. Reporting
  • 21.
     Verify rumours Technical, Administrative and Logistics arrangement  Prepare Outbreak Management Kit according to initial information  Brief members of the investigating team regarding Roles & responsibilities  Methods of personal protection  Team composed of: 1. Nodal officer (Epi/ PHS) 2. Clinician 3. Microbiologist 4. Health Assistant 5. District/ Local administration nominee 6. Other personnel as required
  • 22.
     Verification of thediagnosis is usually made on clinical and laboratory parameters.  Ensure that the problem has been properly diagnosed -- the outbreak really is what it has been reported to be  Review clinical findings and laboratory results for affected people  Visit or talk to several of the people who became ill For outbreaks involving infectious or toxic chemical agents, be certain that the increase in diagnosed cases is not the result of a mistake in the laboratory.
  • 23.
     Incidence rateis calculated by dividing the total cases by the population at risk. 7 ye ar ave rage incide nce vs . 2003 incide nce of D e ngue in 2003 D e lhi av g 2000 1861 1800 1600 1400 n o . o f c as e s  This rate is compared with the rate occurring in the same population, during the corresponding period of the previous years. 1200 1189 1000 800 600 600 0 200 0 0 400 0 0 0 0 0 1 0 0 0 F M A M J 10 4 J 213 2 1 0 J 15 362 A months of reporting 148 101 S O N D
  • 24.
    • • • • • Clustering of casesor deaths Increases in cases or deaths Single case of disease of epidemic potential Acute febrile illness of an unknown etiology Two or more linked cases of disease with outbreak potential(e.g., Measles, Cholera, Dengue, Japanese encephalitis or plague) • • • • • • Unusual isolate (Cholera O 139) Unusual presentation Environmental factors e.g. rainfall, climate Shift in age distribution of cases High vector density Natural disasters
  • 25.
     Rumour register  Tobe kept in standardized format in each institution  Community informants  Private and public sector  Media  Important source of information, not to neglect  Review of routine data – surveillance data  Triggers (There are triggers for each condition under surveillance, Various trigger levels may lead to local or broader response)
  • 26.
     Threshold fordiseases under surveillance that trigger pre- determined actions at various levels  Based upon the number of cases in weekly report  Trigger levels depend on:  Type of disease  Case fatality (Death / case ratio)  Number of evolving cases  Usual trend in the region
  • 27.
    Trigger Significance Levels of response 1 Suspected/limited outbreak • Local response by health worker and medical officer 2 Outbreak • Local and district response by district surveillance officer and rapid response team 3 Confirmed outbreak • Local, district and state 4 Wide spread epidemic • State level response 5 Disaster response • Local, district, state and centre
  • 28.
     Examples:  Trigger levelsfor Dengue  Trigger 1 • Clustering of 2 similar case of probable Dengue fever in a village • Single case of Dengue hemorrhagic fever  Trigger 2 • More than 4 cases of Dengue fever in a village 1000 population.  Triggers for syndromic surveillance  Fever • More than 2 similar case in the village (1000 Population)  Jaundice • More than two cases of jaundice in different houses irrespective of age in a village or 1000 population
  • 29.
    Disease alerts/ outbreaks reported and respondedto by states/ UTs through IDSP; 2nd week (ending 15th January, 2012)
  • 30.
    • Severity ofillness • Number of cases • Source / mode of transmission • Availability of preventive & control measures • Availability of staff & resources • Public, political and legal concerns • Public health program considerations •Potential to affect others if the control measures are not taken • Research opportunity
  • 31.
     Pseudo-outbreaks:  Artifact inthe numerator:  Increased awareness  Reporting of prevalent cases as incident cases (e.g.; hepatitis C, sleeping sickness)  Laboratory error  Variation of the denominator:  Rapidly changing population denominators  Migrants or refugees
  • 32.
     Obtain amap of the area  Counting of the population  Helps to calculate the denominator for further calculation of attack rates.  Provides us with the possible number of people at risk.  Mapping helps us to know area: ecological and environmental factors.
  • 33.
     Map : Detailed,Current map of the area.  If not available – prepare  Information: Natural landmarks, Roads, All dwelling units, Sources of water, Other important features   Counting: Census by age and sex  Lay health workers  House to house visits 
  • 34.
     Includes: Framinga case definition, searching for cases and doing a epidemiological survey.  A case definition is a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest.  Criteria     Clinical and/or biological criteria, Time Place Person  Case definition should be balanced, practical, reliable and applied without bias.
  • 35.
    Example - Measles:3 definitions  Fever and runny nose  Too sensitive  Too many other illnesses produce same symptoms  Call many illnesses “measles”  Fever and rash and Koplik’s spots and conjunctivitis  Too specific  Many cases of measles do not have all these signs  Miss many real cases of measles  IDSP case definition: Fever of 3-7 days duration, with generalized maculopapular rashes; with history of cough, coryza, conjunctivitis or Koplik’s spots.
  • 36.
     Suspect -Fewerof the typical clinical features  Probable- Typical clinical features of the disease without laboratory confirmation.  Confirmed- Typical clinical features with laboratory verification. Confirmed Case Laboratory Verification ++ Possible Case + Clinical Features Probable Case ++ +
  • 37.
     Example: E.coli O157 outbreak at Restaurant X on 31/3/2010  Possible: diarrhea (3 loose stools per day) and ate food purchased at restaurant X on 31/3  Probable: bloody diarrhea and ate food purchased at restaurant X during on 31/3  Confirmed: culture positive with “outbreak” PFGE pattern and ate food purchased from restaurant X on 31/3
  • 38.
     Case Definitionmay need to be updated within an investigation  Broad to specific  Infection with E. coli O157 vs. infection with the outbreak strain (defined by PFGE pattern)  Location of exposure  SARS outbreak (travel within 10 d of onset): • In February: China/HK/Hanoi/Singapore • In April: Toronto, Canada added • In May: Taiwan added  Dates of exposure can change  SARS outbreak: to meet the case definition-dates of exposure dependant on location of exposure
  • 39.
     The firstcases to be recognized are usually only a small proportion of the total number  To identify other cases, use as many sources possible  Passive Surveillance - Relies on routine notifications by healthcare personnel  Active Surveillance - Involves regular outreach to potential reporters to stimulate reporting of specific conditions; investigators are sent to the afflicted area to collect more information  Contact physician offices, hospitals, schools to find persons with similar symptoms or illnesses  Send out a letter, telephone or visit the facilities to collect information  Through media alerts asking people to get checked
  • 40.
    WHY TO SEARCH Icebergphenomenon 40
  • 41.
     The informationis collected by “line listing”.  A line list is like a nominal roll of the cases being reported to the various health care establishments (like dispensaries, general practitioners or admitted to the hospitals)  Constitutes and updates a database of cases  Done by hand or by Excel.
  • 43.
     The surveyteam will go for “door to door” survey in the affected area and ask if any person had suffered with symptoms fitting into case definition (Rapid Household Survey)  If yes, their details were recorded on the epidemiological case - sheet and required samples are taken and dispatched to the hospital/ reference laboratory. Epidemiological case sheet = Case interview form  Detailed information from the case relevant to the disease under study. 
  • 44.
    Information includes: • Name,Age, Sex, Occupation, Social class • Time of onset of disease, Signs & Symptoms • Personal contact at home, work, school • Travel history, attendance at large gatherings • History of previous exposure/injections, • Special events such as parties attended, foods eaten, and exposure to common vehicles such as water, food and milk
  • 45.
     Active door-to-doorcollection of information is by “ Rapid Household Survey”
  • 47.
     Characterizing anoutbreak by time, place and person is called descriptive epidemiology.  Descriptive epidemiology is important because:  What is reliable and informative (e.g., similar exposures)  What may not be as reliable (e.g., many missing responses to a particular question)  Provides a comprehensive description of an outbreak by showing its trend over time, its geographic extent (place) and the populations (people) affected by the disease
  • 48.
     Development of proportional distributionof cases according to host characteristics (age, race, sex) or by exposures (occupation, leisure activities, use of medications, tobacco, drugs).
  • 49.
     Count  Count thecases in each age and sex groups  Divide  Obtain census denominators for each age and sex groups  Compare  Estimate the incidence for each:  Age group  Sex group
  • 50.
     An attackrate is the proportion of a well-defined population that develops illness over a limited period of time, such as during an epidemic or outbreak  What are the age and gender specific attack rates?  What age and gender groups are at highest and lowest risk of illness?  In what other ways do the characteristics of the cases differ significantly from those of the general population? Purpose => Identification of sub-group(s) at risk
  • 51.
    Attack rate ofmeasles by age and sex, Cuddalore, Tamil Nadu, India, 2004-2005 Characteristics Age group Number of Population cases Attack rate per 100,000 255,755 19.6 51 1,795,383 2.8 Male 48 1,032,938 4.6 Female Total 50 5+ Sex 0-4 53 1,018,200 5.2 101 2,051,138 4.9
  • 52.
    100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Protestants Coptic Christians Muslims Population Cases ofBotulism BOTULISM OUTBREAK IN CAIRO, EGYPT - APRIL1993 Weber JT, Hibbs RG Jr, Darwish A, et al. A massive outbreak of type E botulism associated with traditional salted fish in Cairo. J Infect Dis 1993; 167: 451-454
  • 53.
    What is theexact period of the outbreak? What is the probable period of exposure? Is the outbreak likely common source or propagated?
  • 54.
    Drawing the epidemiccurve based on time distribution of cases 2. Eyeball distribution to choose interval 1. Count cases by time of onset 3. Finalize
  • 55.
     Interpretation ofepidemic curve Shape – type of epidemic  An early case in the curve may represent source of the epidemic  Give information about the time course of an epidemic and what the future course might be  In a point-source epidemic of a known disease with a known incubation period, epidemic curve provides information to identify a likely period of exposure  Shape of epidemic curve illustrates type of epidemic. 
  • 56.
  • 57.
    Common source singleexposure:  Sharp increase followed by a rapid decline.
  • 58.
    Continuous common sourceoutbreak:  An abrupt increase in the number of cases but, new cases persist for a longer time with a plateau shape instead of a peak before decreasing.
  • 59.
    • Intermittent commonsource: multiple peaks
  • 60.
     Propagated sourceoutbreak: Number of cases  Increase in the number of cases with progressive peaks 16 14 12 10 8 6 4 2 0 1 4 7 10 13 16 19 22 25 28 31 34 Date
  • 61.
     The spatialrelationships of cases are shown best on a spot map.  A spot map showing the location of cases can give an idea of the source of infection like maps show that the cases occurred in proximity to a body of water, a sewage treatment plant, or its outflow. DRAWING A ROUGH SPOT MAP
  • 63.
     Questions tobe asked and answered:  What is the most significant geographic distribution of cases?  Place of residence? Workplace?  Do the attack rates vary by place?  Relation to any landmark or possible source?
  • 64.
     Usually we generatehypotheses from the beginning of the outbreak, however, at this point, the hypotheses are sharpened and more accurately focused.  To consider what is known about the disease itself: What is the agent’s usual reservoir? B. How is it usually transmitted? C. What vehicles are commonly implicated? D. What are the known risk factors? A.
  • 65.
     Talk topeople who are ill: In-depth open interviews, Group discussions  Hypotheses should be proposed in a way that they can be tested.
  • 66.
     After ahypothesis is formulated, one should be able to show that:  all additional cases, lab data, and epidemiologic evidence are consistent with the initial hypothesis  no other hypothesis fits the data as well  Observations that add weight to validity:  The greater the degree of exposure (or higher dosage of the pathogen), the higher the incidence of disease  Higher incidence of disease in the presence of one risk factor relative to other factors
  • 67.
     Approaches:  Comparisonof hypothesis with known/ established facts.  Analytic epidemiology to test the hypothesis  First method is used when the evidence is so strong that hypothesis need not be tested  Example - A 1991 investigation of an outbreak of vitamin D intoxication in Massachusetts. All affected drank milk from local dairy. Hypothesis - dairy was source, milk vehicle of excess vit D. Visit to dairy, they quickly recognized that far more than the recommended dose of vitamin D was inadvertently being adding to the milk. No further analysis was necessary.
  • 68.
     Analytic epidemiologyis used when cause is less clear. Cohort studies  Case control studies   What to use? Case control Rare disease/ large community Common disease/ small community Complete population accessible Large amount of resources Limited resources Cohort +++ - - +++ +/- +++ + ++ +++ -
  • 69.
    Example: Case control studyfor an outbreak of Acute Gastroenteritis following a dinner. FOOD ATE and ILL N (%) ATE and NOT ILL N (%) ODDS RATIO TOMATOES 14 (82) 30 (86) 0.83 CHICKEN 13 (71) 34 (94) 0.11 ALFAALFA SPROUTS 10 (67) 6 (17) 8.25
  • 70.
     These areadditional studies undertaken to corroborate the findings of the epidemiological study.  Environmental studies  Microbiological studies  Entomological studies
  • 71.
     Environmental studiesoften help explain why an outbreak occurred and may be very important in certain settings.  Example: Site of contamination of irrigation canal with cattle urine in an outbreak of Leptospirosis in southeastern Washington, August 1964. Pond connected to irrigation canal And Cattle around the site
  • 72.
     Microbiological studiescan clinch the relationship between suspected source and outbreak.  Example: In the above outbreak of Leptospirosis, culture of urine from the cattle, water of the canal and blood of affected children yielded the same strain of L. pomona. Also, the children who had recovered showed increased anti leptospiral antibodies.
  • 73.
     Entomological studieshelp identify the vector responsible for the outbreak.  May also give useful insight into the life cycle of the pathogen and the mode of transmission Example: Vector surveillance in Chikungunya affected villages of Latur and Beed districts of Maharashtra, 2006
  • 74.
     Additional epidemiologicstudies  What questions remain unanswered about the disease?  What kind of study used in a particular setting would answer these questions?  When analytic studies do not confirm the hypotheses  reconsider the original hypotheses  look for new vehicles or modes of transmission  Additional investigations  Further lab studies  Refine hypothesis till confirmation
  • 76.
     Report providesa blueprint for action.  It also serves as a record of performance and a document for potential legal issues.  It serves as a reference if the health department encounters a similar situation in the future.  In public health literature serves the purpose of contributing to the knowledge base of epidemiology and public health  Daily interim reports and final report.
  • 77.
    Contents of aReport: 1. Back ground 2. Historical data 3. Methodology of investigation 4. Analysis of data (clinical data, Epidemiological data, modes of transmission, Lab data, Interpretation of data) 5. Control measures 6. Evaluation 7. Preventive measures
  • 78.
    Report to besubmitted by investigating officer/ team to the next higher authority within one week of completion of investigations
  • 79.
     Appropriate controlmeasures  based on Epidemiological, Clinical, Environmental findings  To prevent further spread of disease  The elements of epidemic control include: 1. Controlling the source of the pathogen (if known) Remove or inactivate the pathogen 2. Interrupting the transmission. Sterilize environmental source of spread; vector control 3. Modifying the host response to exposure. Immunization; Prophylactic chemotherapy
  • 80.
     Control measuresshould be implemented at the earliest.  DO NOT wait for laboratory confirmation to start control measures.
  • 81.
     Follow upof outbreak  Detect last case  Detect and treat late complications  Complete documentation  Evaluation of outbreak management including investigations (by local authorities) Genesis of outbreak  Early or late detection of outbreak  Preparedness for outbreak  Management of the outbreak  Control measures taken and their impact 
  • 82.
     Documentation andsharing the lessons learnt Post outbreak seminar.  Feedback to local health authorities, RRTs and other concerned.  Developing case studies on selected outbreaks for training purposes. 
  • 83.
    Audience Medium Focus of the content Communication objective Epidemiologists, laboratory •Report •Epidemiology •Documentationof the source Public health managers •Summary •Recommendations •Action Political leaders •Briefing •Control measures •Evidence that the situation is under control Community •Press release, interview •Health education •Personal steps towards prevention Scientific community •Presentation, manuscript •Science •Scientific progress POSSIBLE MATRIX FOR COMMUNICATION OF INVESTIGATION RESULTS AND FINDINGS
  • 84.
     An outbreakof fever, URI & loose motion among the boarders of PTS, Jharoda kalan, Delhi was reported to the MS of SJH by CDMO of SW district of Delhi on 10.07.09 .  Cause for concern – Panic d/t novel H1N1 cases in Delhi  RRT composition – Epidemiologist, Physician, Microbiologist and other doctors. (11.07.09)  Case definition: A person with acute onset of fever with or without sore throat, diarrhea, headache, body ache starting from 2nd July 2009 onward.  Line listing, Epidemiological case sheet (with travel history), Lab analysis of samples for H1N1.
  • 85.
     Descriptive: Time –Start = 2nd Jul, Peak = 7th Jul, Fall afterwards  Place – Start in Tent # 40, 25 & 8; then spread. clustered around tent no 1,9,20, 22, 27, 36 &37.  Person – 61 cases. Mean age 22.2 yrs (20-49).   Environmental: Crowded, ill ventilated tents. Humid environment with low temperature.  Lab: H1N1 negative. Influenza A +ve.  Recommendations:    Reduce crowding, Improve ventilation Increase staffing in dispensary and Proper record maintainance Prompt identification and reporting of changes in disease frequency.
  • 86.
     Outbreak ofjaundice among the residents of Sector 8 of RK Puram, New Delhi was reported to the MS of SJH by CDMO of SW district of Delhi on 06.04.2011.  Initial report by DSO suggested sudden onset of jaundice.  RRT – Epidemiologist, Physician, Microbiologist and other personnel. To CGHS, dispensary on 06.04.2011  Case defn : A person with signs and symptoms of jaundice with or without elevated serum aminotransferase levels from 1st January 2011 onwards  Verification of outbreak by review of records of CGHS dispensary.
  • 87.
     Rapid survey,Line listing, Spot map, Clinical examination, Epidemiological case sheet, Blood samples, Environmental study  Descriptive: Time – Rise from 15th Jan, Peak 1st week March, Decline afterwards. Max cases in March (11/21)  Place – Clustering around N block & adjacent to Palam rd  Person – 15-30 yrs (50%), M > F (58.3/ 41.7)   Lab: 3/5 recent cases +ve for Anti HEV IgM. 2/6 water samples – Fecal contamination
  • 88.
     Environmental: Water& sewer lines running close, Intermittent water supply – Booster pumps, Latrine near water storage tank, Sewer lines not de-silted – overflowing, Damaged water lines. Absent residual chlorine.  Conclusion: Confirmed outbreak of jaundice. Lab results  Acute Hepatitis E. Damaged water lines and contamination from sewer lines responsible.  Recommendations: Proper record maintenance in CGHS dispensary(diagnosis, S/s)  Monitoring and repairing of water lines  Sewer lines should not be close to water supply pipeline  Regular de-silting and cleaning of sewer line.  Proper chlorination of water supply. 
  • 89.
    1. A Dictionaryof Epidemiology – 3rd ed; Last JM. 2. 3. 4. 5. 6. 2000. Park’s Textbook of Preventive and Social Medicine – 21st ed; Park JE. 2010. Epidemiology – 4th ed; Gordis L. 2004. Checklist for CRRT for outbreak investigation, NICD 2008 Oxford Textbook of Public Health – 4th ed; 2002 Mausner & Bahn Epidemiology: An Introductory Text – 2nd ed; Mausner JS, Kramer S. 1985.
  • 90.
    7. R Bonita,R Beaglehole, T Kjellström. Basic Epidemiology: WHO;2nd Edition. 8. Outbreak Investigations Around The World: Case Studies in Infectious Disease Field Epidemiology; Mark S Dworkin. 2010 9. Steps of outbreak investigation; Epidemiology in the classroom. Excite, CDC. From www.cdc.gov 10. Raut DK, Roy N, Nair D, Sharma R. Influenza A virus outbreak in Police Training School, Najafgarh, Delhi – 2009. Indian J Med Res; Dec 2010; 132: 731-732
  • 92.
    LARGE OUTBREAKS FROMAROUND THE WORLD – WHO, 1999

Editor's Notes

  • #4 1= Last, 2= Park, 3= Gordis
  • #5 4=checklist for CRRT for outbreak investigation, NICD 2008
  • #6 The term ‘cluster’ is an aggregation of two or more cases which is not necessarily more than expected.
  • #18 Magnitude : Measurement of epidemic in terms of morbidity, mortality , loss of productivity, psychological influence on population affected.
  • #58 Epidemic curve: a graphic plotting of distribution of cases by time of onset.
  • #86 Limitations: delay in initial report. Improper records. Problems: No evaluation. No follow up. Surveillance system should have been started.
  • #88 Blood samples from 5 recent and 4 convalescent cases
  • #89 Late start d/t late info.Investigation not evaluated. No system created for early detection of outbreakRecommendation of sewer and water line distance not practical ???No follow up