Investigation of Disease Outbreaks

Objectives of the investigation of epidemic

1. Define and research for the correct conclusion regarding the agent, source, mode of spread, distribution, and duration.
2. Determine the most effective and practical means of controlling the epidemic and preventing future recurrences of similar nature.
3. To provide health services.
4. To maintain or improve epidemiological surveillance by personal and direct contact.
5. To establish epidemiological surveillance system.
6. To provide training opportunities in practical field outbreak investigation.

Solutions of Epidemic problems

The investigation of epidemics requires answers to these questions:

1. Is there actually an epidemic?
2. What ar the characteristics?
3. What seems to have caused it?
4. What must be done to provide the actual caused?
5. How can it be stopped or prevented?

Procedure in Investigation of an Epidemic

Before the outbreak investigation, followings need to be discussed and agree upon:

• Resources (including personal) will be available locally
• What resources will be provided regional team
• Who will direct day to day investigation
• Who will provide overall supervision and ultimately be responsible for investigation
• How will the data share and who will be responsible for their analysis
• Will the report of the findings be written, who will write it, to who will it go
• Who will be the senior author of a scientific paper

It is important to have technical knowledge of epidemiology for the definite and correct conclusion during an epidemic investigation. The derived conclusion must be correct, honest, logical, simple and consistent with convincing proof which is necessary for adoption to the understanding pf the audience. Although not rigid, the following steps should be followed to get a reasonable conclusion.

I.Preparation for field work and definition of problem

During the preparation of the field, the outbreak investigation and response team need to be well aware that what disease or health problem they need to investigate. Consultation with the subject expert to get his opinion and more information to manage the health problem effectively is important before start. Likewise, administrative arrangements for logistics, medicine, laboratory supplies and equipment, transportation, travel plan and field expenses should be made.

a. Verify the diagnosis using a firm "case definition"

The reports of the cases in the outbreak area should be considered for correctness and reliability. Criteria should be established for diagnosis ( or labeling persons as cases), which may be based on symptoms, laboratory results, or both. Cases should be confirmed by clinical and/or laboratory diagnosis.

b. Verify the existence of an epidemic

To verify the existence if an epidemic, current incidence should be compared with its incidence in the past in the same population group and at the same time of the years. This depends on the validity and accuracy of the diagnosis of the present and of the past cases. The source of the data might be surveillance data or morbidity/mortality statistics.

Note:This step will give the answer to the question " Is there actually an epidemic?"

The cases that did not attend hospitals or clinics must be searched for to get maximum number of cases due the epidemics. The sources of information might be either the cases (where they had siblings or neighbours who had similar sign and symptoms) themselves or surveys of health care facilities in the community.

II. Appraisal of existing information

The collected epidemic information/data should be arranged according to time, place and person.

Time:This is the chronological distribution of onsets of cases by time (hour, day, week, and month). The epidemic curve should be plotted to get clear implication due time factor. The character of the epidemic curve is determined to ascertain whether it suggests that a group of people were infected at or about the same time. The probable time of infection is estimated on the basis of the incubation period of the disease. An explosive epidemic with short duration generally indicates:

• A common source of infection
• Exposure occurs over a brief period of time
• A large number of susceptible hosts exposed
• A high infectivity
• An incubation period of little variation

Place:The disease mapping indicates reservoir and source of infection. The cases are plotted by a location mapping or spot map, using a pin to represent a case (or a group of acase) with different colors to show different days or week of onset. The movement and direction of an epidemic is important for control measures. Environmental condition e.g. water and milk supply, sanitation of restaurant, food storage etc. should be reported in the map.

Person:Affected persons and their characteristics should be identified. Analysis of the available information on population and the confirmed reported cases and deaths should be done according to race, sex, age, occupation, and place of residence, recent migration; to identify what groups of people are at risk.

Note:This step will give the answer to the question "what are its characteristics?"

III. Formulation of Hypothesis

Descriptive characteristics are used to identify the possible factors that caused the disease. The incidences or attack rates among various groups are compared. The risk group and the common source or sources to which the members were exposed are identified.

This step explains about the cause of the disease and suggests for blocking the progress of the disease, and serving as a guide for further investigation.

Note:This step will give the answer to the question "what seems to have caused it?"

IV. Testing of hypothesis

Analytical studies such as case control or cohort are carried out and data are analyzed using statistical test (e.g. attack rate, relative risk, or chi- square test) to determine probable sources. Differences between those exposed and unexposed to the risk factor of the disease is determined. Attrubutable risl is also calculated. These analysis help to search for other possible sources of infections or other modes of transmission. Epidemiologic findings should be confirmed by laboratory test of specimens such as blood, feces, suspected food, etc.

Sometimes, various facts or hypotheses may fit with the result by analysis. Therefore, it is essential to test various hypotheses to ascertain whether it is consistent or inconsistent with all the known facts.

Note:This step will give the answer to the question "what must be done to prove the actual cause?"

V. Conclusion of the investigation

The conclusion must be baed upon all pertinent evidences, which should be consistent with only one hypothesis. Incomplete studies may give false lead to future prevention.

VI. Report of the investigation and dissemination

Afinal report with discussion of factors leading to the epidemic, recommendations for control or prevention of similar diseases in th future, and evaluation of the measures used for control of the epidemic should be prepared. Dissemination of outbreak invetigation report needs to be made at different level, e.g. at community (village) level, very simple presentation needs to be given to brief the community about the causes of outbreak and its prevention. At district level, more technical report needs to be submitted and scientific paper needs to be written for publication in scientific journals.

Note:Step V and step VI will give the answer to the question "how can it be stopped and others prevented?"

Management of Epidemic

It is the task of government health sector to manage the epidemic. The management comprises the following componenets:

• Treatment of cases and carriers
• health education on sources of infection and modes of transmission
• Immunization
• Isolation/ quarantine
• Elimination and/ or disinfection of reservoir and sources pf infection
• Surveillance

References

Gordis, L. Epidemiology. third edition. 2004.

Joshi, Banjara. Fundamentals of Epidemiology. Kathmandu: Quality Printing Press, 2007

Park, K. Park's Text Book of social and prevention Medicine. 18th edition. 2008.