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Investigation of an Epidemic

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1 Investigation of an Epidemic


3 Introduction Source of information regarding epidemic Warning signs of an impending epidemic Purpose of Epidemic investigation Epidemic Investigation Team Prior to implementation of Investigation Steps to investigate an Epidemic

4 Introduction EPIDEMIC. The occurrence in a community or region of cases of an illness, specific health related behavior, or other health related events clearly in excess of normal expectancy. ( Last ) OUTBREAK. Synonymous with epidemic. Sometimes the preferred word, as it may escape sensationalism associated with the word epidemic. Alternatively, a localized as opposed to generalized epidemic. CLUSTER. An aggregation of cases of a disease or other health-related condition, particularly cancer and birth defects, which are closely grouped in time and place. The number of cases may or may not exceed the expected number; frequently the expected number is not known

5 EPIDEMIC OR OUTBREAK … Some epidemiologists prefer to use the term epidemic only in a situation that covers a very wide geographical area and involves large populations. For example, it is possible to use the term 'outbreak of HIV' to describe a sharply increasing HIV prevalence rate among commercial sex workers in a city where the normal rate was low in the previous year. But the term 'HIV epidemic' can be used when an abnormally high HIV prevalence is found among sex workers in many cities of the country. Because the criteria for judging an outbreak can be very subjective, it is useful to define the term in a more measurable fashion.

6 The criteria for judging an epidemic/outbreak
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. For example, the epidemic of Kaposi's sarcoma, a manifestation of AIDS, was confirmed in New York when almost 30 cases were reported in 1981, whereas only two or three cases had been reported in previous years A cluster of cases of the same disease occurs which can be linked to the same exposure. The term 'cluster' is an aggregation of two or more cases which is not necessarily more than expected. 3. 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.

7 Source of information regarding epidemic
I ) Health personnel Doctors and nurses in a hospital have a good opportunity to observe an abnormal increase in the number of patients with a particular disease or syndrome II) Laboratory Every laboratory or network can serve as an excellent source of outbreak notification. The avian flu outbreak in the Hong Kong Special Administrative Region was first discovered by the Influenza Surveillance Network, which reported an abnormal influenza ,type A (H5N1) III) Official disease notification systems Most countries have official systems for notification of cases and deaths from specific diseases from hospitals IV) Newspapers or media V ) Village health volunteers Vi ) Rumour Register  In rural areas where there are no health facilities and communication is limited, village leaders or village health volunteers can often help to recognize an abnormal increase in the numbers of some clinical diseases such as diarrhoea, dysentery, measles, fever, death of unknown aetiology, and so on.

8 III. Warning signs of an impending epidemic
Clustering of cases or deaths in time and/or space Unusual increase in cases or deaths Even a single case of measles, AFP, Cholera, Plague, dengue or JE Acute febrile illness of unknown aetiology Occurrence of two or more epidemiologically linked cases of meningitis, measles Unusual isolate Shifting in age distribution of cases High vector density Natural disasters

9 Purpose of outbreak investigation
Controlling the current outbreak Prevention of future outbreaks Research to provide knowledge of the disease 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 I

10 Components of an investigation team .
The term 'investigators' will represent the people who are directly involved in planning and conducting the outbreak investigation from start to finish 1. A field epidemiologist who is technically competent to conduct field investigations systematically 2. Disease control people who are experienced in implementing basic disease control measures such as food and environmental sanitation, vector control, vaccination 3. Laboratory technicians who are able to provide basic and advanced laboratory support to the investigative team 4. Specialists in particular areas; for example, a veterinarian would be very helpful for an outbreak investigation of zoonotic diseases. eg. Entomologist, Social Scientist 5. Public health administrators, who are good at providing logistic support, mobilizing resources, and providing administrative expertise for the team 6. Public relations person

11 The Rapid Response Team (RRT):
A suggested composition of this team is an epidemiologist, a clinician and a microbiologist. The main role of the RRT will be to investigate and confirm outbreaks. RRT is not a permanent team who is waiting for an outbreak. Individuals who are normally performing their usual roles, but in the event of an outbreak come together to undertake a special function. Should work in close coordination with the local health staff in the event of an outbreak. Help and support the local staff in the management and control of the outbreak, the prime responsibility for implementing control measures rests with the local health staff (with additional support from the district health authorities). The names, addresses and telephone numbers of the RRT members should be available with the District and State surveillance officer at all times, so that they can be activated as soon as possible. Members who have been transferred etc should be replaced with competent people as soon as possible.

12 Prior to the implementation of an investigation
Assessing the existence of the outbreak Gathering the available basic information Information related to the disease situation Information related to control and response activities  Ensuring that clinical specimens and suspected materials were collected Obtaining permission and adequate support from the local and national authorities Field operation plan Reviewing current knowledge of the outbreak

An outbreak investigation : Observational study in nature because the events have already happened. Every outbreak investigation needs to start with a good descriptive study followed by analytical studies whenever possible and necessary. Conclusions about the causes, mechanisms, and determinants of the outbreak need to be based on sound epidemiological, clinical, laboratory, and environmental evidence. It is preferable to translate the methodology for outbreak investigation into steps of action. Gregg (1996) has divided the outbreak investigation process into 10 steps.

14 Ten steps to take in an outbreak investigation
Confirm the existence of the outbreak Verify the diagnosis and determine the aetiology of the disease Develop a case definition, start case-finding, and collect information on Cases Describe person, place, and time and generate hypotheses Test hypotheses using an analytic study Do necessary environmental or other studies to supplement epidemiological study Draw conclusions to explain the causes or the determinants of Outbreak based on clinical, laboratory, epidemiological, and environmental evidence Report and recommend appropriate control measures to concerned Authorities at the local, national, and, if appropriate, international levels Communicate the findings to educate other public health professionals and the general public Follow-up of the recommendations to assure implementation of control Measures This outline of steps for outbreak investigation does not imply a strict sequence of action. In real outbreak investigation, many steps can happen at the same time depending on the situation

15 Step 1: Confirm the existence of an outbreak
The main question is: Is this a true outbreak? Applying the definition of an outbreak outlined , the investigator should be able to establish or refute the existence of the outbreak. Investigators should review the number of cases with the local health officers or hospital staff and compare it with the number found at the same period recorded in past years. For example, the outbreak of trichinosis in North Rhine-Westphalia, Germany, was confirmed because there were 52 cases in a 3-month period between November 1998 and January 1999 compared with no more than 10 cases annually during the same time period in the past 10 years

16 Step 2: Verify the diagnosis and aetiology of the disease
If number of cases fit the case criteria for the outbreak, the next related questions are: What is the correct diagnosis and aetiology of the disease? What can be done immediately to prevent new cases from occurring? Will protect susceptible people and allow the team to start education of villagers to avoid the risk factors  Investigators should have basic knowledge of clinical diagnosis and how to confirm the aetiology of suspected diseases by well-established laboratory techniques Investigators should visit and talk with some patients, review and visualize the signs and symptoms, and hold discussions with the attending doctors. ( Help to develop a case definition to facilitate active case-finding.) Investigators should also visit laboratory facilities and ask for either positive or negative results of the testing of specimens It is not necessary that cases have to be laboratory confirmed, but at least some of the apparent clinical cases or deaths should be confirmed. In many situations, an unknown or unclear diagnosis can cause panic due to rumour. This is demonstrated by an outbreak of pneumonic plague in Surat, India, in 1994 and of encephalitis in Malaysia in 1999, which resulted in a severe panic among local people and foreign tourists. Thus it is very important to obtain the exact diagnosis as rapidly as possible.

17 Step 3: Develop an appropriate case definition, start case-finding, and collect information on cases
At this stage, the investigator needs to answer at least three questions. Who should be counted as cases? Are there more undetected cases in the hospitals and in the community? What are the characteristics of cases? To answer these three questions the investigators must follow these three small steps. i) Developing an appropriate case definition ii) Active case-finding iii) Collecting information on cases ( Identifying information, Demographic information, . Clinical information, Suspected risk factors

18 Step 4: Describe the outbreak in person, place, and time, and hypotheses formation
What are the main clinical features? Who is the population at risk? What are the risk factors? What are the most likely explanations of how the outbreak began? The simple approach is to analyse clinical information from each case and see the distribution of factors in terms of person, place, and time. Analysis should be done using rates rather than absolute numbers. The investigator needs to obtain the denominators from an available source or to estimate them. Using rates, the investigator can compare and determine the populations and areas of highest risk. With the advent of computers, many software programs are available to analyse this data.

19 Clinical manifestation of cases
Signs and symptoms of cases can be analysed in percentages and shown in a summary table eg. Line Listing of cases Index case Investigators should analyse the characteristics of cases by sex, age, occupation, ethnicity, and so on Specific attack rate by age and sex will be more useful Place Investigators can calculate the attack rate of cases by different places. A spot map showing the location of cases can give a very good idea of the source Time Distribution – Epidemic Curve





24 Step 5: Testing the hypotheses by analyses
In an outbreak of infectious disease, the investigator needs to answer the following questions. What is the aetiology of the disease? What is the source of infection? What is the pattern of spread? What are the risk factors for an individual to get the disease? What are the determinants of the outbreak or the factors which when combined together result in the outbreak? For example, a cholera outbreak in a home for mentally disabled children persisted over a 1-month period and the epidemic curve showed a pattern of person-to-person spread. After looking into the attack rate in different buildings in the home the investigator found that some buildings had a very high attack rate. When the investigator visited the home he discovered that the building with the high attack rate was very crowded. Two or three children had to share one single bed. The children also bathed in a small room where they were exposed to faeces from other children. With this direct observation, the hypothesis was formulated that crowding promoted the spread of the disease

25 Step 6: Environmental or other studies to supplement the epidemiological findings  
Investigator needs to find environmental or other evidence to support and explain the epidemiological evidence. Outbreak of unknown illness in a rural village of Egypt : Cases developed severe abdominal pain, persistent vomiting, and generalized weakness, the investigator was able to detect abnormally high blood lead levels among the cases. Analytical study revealed an association between high blood level and eating flour from one mill factory. Mill implicated in the outbreak was visited. Upon arrival at the mill, the investigators noted a lead smelting pot in the corner of the mill. Lead was used by miller to attach the crosspiece to the grinding stone. Occasionally, the lead would break off and contaminate the flour. The miller reportedly used about 2 kg of lead per year Analysis of grain from the mill showed no lead; however, lead was found in flour from the surface of the mill stone and in samples of flour after grinding was complete

26 Step 7: Establishing the causes of the outbreak
Laboratory evidence Clinical evidence Environmental evidence Epidemiological evidence This epidemiological evidence found in the descriptive and analytical studies should clearly explain the following aspects: Pattern of spread as described by epidemic curve Statistical strength of association between exposure and developing the disease Dose–response relationship, which demonstrates a higher strength of association when the exposure is increasing exposure should precede illness.

27 Step 8: On-site reporting and recommendations for concerned authorities  
Complete the analysis and data interpretation Leaving the field without completing these tasks will reduce the sense of urgency necessary to finish the work. Data are easier to retrieve when in the field rather than instructing the field people to send them to the investigative team later. Present the main findings with recommendations. Some findings may be very sensitive because they reflect the weaknesses or mistakes of the health or other authorities. The investigator needs to select the appropriate approach, either formal or informal, with the responsible people.

28 Step 9: Dissemination of the information
In addition to on-site reporting, the investigator should disseminate the information to educate the public health community and the general public. There may be many other communities that are also prone to a similar outbreak. The information will raise the awareness of health and government authorities to assess their own situation and implement some measures to prevent possible outbreaks. The dissemination of information should be done in a timely manner through weekly or monthly reports

29 Step 10: Follow-up to ensure implementation of control measures
Finally, the investigator should follow-up the investigation by maintaining close communication with the local health authorities. An absence of new cases for at least two incubation periods of the infectious disease under investigation could suggest that the outbreak is subsiding. A good investigator should follow up on the recommendations. An outbreak investigation is a waste of time if good recommendations have not been implemented. The investigator should learn the reasons why the recommendations were or were not implemented. If the recommendations were implemented, the investigator can also learn the impact by observing the trend of the diseases.

30 REPORTS It is important for concerned officials to make appropriate
and timely reports to higher authorities. 1. It keep the authorities at the higher level informed so that they can make the appropriate decisions 2. It helps to review the outbreak and response, identify system failures and take corrective measures so that similar events are not repeated. Some of the reports recommended are: 1) Preliminary report by nodal MO: The nodal MO of the peripheral health facility who first reports the outbreak should submit a preliminary report to the next level. The report should cover briefly about how the outbreak came to his attention, verification of the outbreak, total number of affected cases/ deaths, time, person, place analysis, management of the patients, likely suspected source, immediate control measures implemented

31 2) Daily situation updates
During period of the outbreak ,nodal MO should continue to give daily situation updates of the outbreak to the next level. This should continue even when the EIT has started its investigation and should include the list of new cases, lab results received, any new findings, any containment measures etc This daily report should continue till the end of the outbreak (i.e. no suspect case during a period which is double the incubation period). Interim report by RRT The RRT will submit an interim report within one week of starting their investigation, response and control activities. The report should cover verification of the outbreak, total number of affected cases/ deaths, time, person, place analysis, management of the patients, likely suspected source, immediate control measures implemented, etc. The report will include reports by the physician and microbiologist, and entomologist (where applicable),lab results received during that period, environmental factors, etc. It will also have a provisional hypothesis of the causation of the outbreak and comments/recommendations, if any, including whether any further outside help is necessary.

32 4) Final report Within 10 days after the outbreak has ceased, a final outbreak investigation report must be submitted by the local health authorities. This report must be comprehensive and give a complete picture of the multi-factorial causes of the outbreak, the precipitating factors, the evolution of the epidemic, description of the persons affected, time trends, areas affected and direction of spread of the epidemic. It should have complete details of lab results including regional lab (cross verification and strain identification), confirmation of the provisional diagnosis and other relevant information. It is important that feedback from the report is shared with the lower levels and also other districts.

33 Declaring the outbreak to be over
The DSO / MHO should declare the outbreak to be over only when there have been no new cases for a period of 2 incubation periods since the onset of the last case. This implies that a very active case search should continue during this period to ensure that cases are not missed.






















55 REFERENCES Detels R, Beaglehole R, Lansang MA, Gulliford M. Oxford textbook of public health. Volume 2 . Methods of public health. 5th edition, Oxford University Press, 2009. IDSP Training Manual- Chapter 6 Textbook of public health. AFMC, Pune in collaboration with WHO India Country Office. Beaglehole R, Bonita R, Kjellstorm T. Basic epidemiology. WHO, Geneva, 2002. Gordis L. Epidemiology. Third edition, Elsevier Saunders. 2004


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