Outbreak Investigation Dr Tauseef Ismail

Outbreak A sudden increase in the number of individuals who contact a specific infectious disease in a population, putting others at risk. OR Spread of disease, which occurs in a short period of time and in a limited geographic location (i.e, neighborhood, community, school, or hospital)

Outbreak Investigations Three critical variables in investigating an outbreak or epidemic are: When did the exposure take place? When did the disease begin? What was the incubation period for the disease?

Steps of an Outbreak Investigation

Steps of an Outbreak Investigation Preparation Confirm the existence of outbreak Verify the diagnosis Establish a case definition Find cases systematically & record information Perform descriptive epidemiology Develop hypotheses Evaluate hypotheses epidemiologically As necessary, reconsider, refine, and re-evaluate hypotheses. Implement control and prevention measures Communicate findings

1. Preparation Scientific knowledge Supplies Equipment Investigation Review literature Consult experts Sample questionnaires Supplies Consult with laboratory Equipment Laptop, camera etc. As a field investigator, you must have the appropriate scientific knowledge, supplies, and equipment to carry out the investigation before departing for the field. Discuss the situation with someone knowledgeable about the disease and about field investigations, and review the applicable literature. In previous similar outbreaks, what have been the sources, modes of transmission, and risk factors for the disease? Assemble useful references such as journal articles and sample questionnaires. Before leaving for a field investigation, consult laboratory staff to ensure that you take the proper laboratory material and know the proper collection, storage, and transportation techniques. By talking with the laboratory staff you are also informing them about the outbreak, and they can anticipate what type of laboratory resources will be needed. You also need to know what supplies or equipment to bring to protect yourself. Some outbreak investigations require no special equipment while an investigation of SARS or Ebola hemorrhagic fever may require personal protective equipment such as masks, gowns, and gloves.

2. Establish existence of an outbreak Is an outbreak truly occurred? through surveillance records for notifiable diseases. hospital data. data from other facilities community survey.

3. Verify the Diagnosis Ensure proper diagnosis and rule out lab error as the bias for increased diagnosis Review clinical findings, lab results

Verify the Diagnosis cont. See and talk with patients if at all possible Better understand clinical features Gather critical information Source of exposure What they think caused illness Knowledge of others with similar illness Helpful in generating ideas for hypothesis about etiology and spread

4. Establish a case definition Includes clinical criteria and restrictions by time, place and person Classification Definite (confirmed) Laboratory confirmed Probable Typical clinical features without lab confirmation Possible (suspected) Fewer of the typical clinical features A case definition is a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest. A case definition includes clinical criteria and — particularly in the setting of an outbreak investigation — restrictions by time, place, and person. The clinical criteria should be based on simple and objective measures such as "fever ≥ 40°C (101°F)," "three or more loose bowel movements per day," or "myalgias (muscle pain) severe enough to limit the patient's usual activities. " The case definition may be restricted by time (for example, to persons with onset of illness within the past 2 months), by place (for example, to residents of the nine-county area or to employees of a particular plant) and by person (for example, to persons with no previous history of a positive tuberculin skin test, or to premenopausal women). Whatever the criteria, they must be applied consistently to all persons under investigation.

Meningococcal Disease — PAHO (Pan American Health Organization) Case Definition Clinical case definition An illness with sudden onset of fever (>38.5°C rectal or >38.0°C axillary) and one or more of the following: neck stiffness, altered consciousness, other meningeal sign or petechial or puerperal rash. Laboratory criteria for diagnosis Positive cerebrospinal fluid (CSF) antigen detection or positive culture.

Case classification Suspected: A case that meets the clinical case definition. Probable: A suspected case as defined above and turbid CSF (with or without positive Gram stain) or ongoing epidemic and epidemiological link to a confirmed case. Confirmed: A suspected or probable case with laboratory confirmation.

Example: Case Definition for Hepatitis A Confirmed case: – Anti-HAV IgM+ Probable case: Pale skin Suspect case: Any two of the following: Abdominal pain, fever, nausea, anorexia, malaise

5. Find cases systematically & record information Target health care facilities where diagnosis is likely to be made Enhanced passive surveillance e.g. letter describing situation and asking for reports. Active surveillance e.g. phone or visit facility to collect information Alerting the public Media alert to avoid contaminated food products and seek medical attention if symptoms arise.

5. Find cases systematically & record information contd…. Identifying information Name, address, and telephone number is essential if need to contact patients additional questions. Also to Notify them of lab results and outcomes of investigation Names also helps in checking for duplicate records while addresses allow for Mapping the geographic extent. Demographic information. Provide “person” characteristics for defining population at risk

5. Find cases systematically & record information contd…. Clinical findings Signs and symptoms allow to Verify that the case definition has been met Date of onset is needed to Chart the time course of outbreak. Reporter information Id of person making report

5. Find cases systematically & record information contd…. Line listing Abstraction of selected critical items from above information

What is a Line Listing? A rectangular database similar to spreadsheet Provides summary of key data about cases in an outbreak Each row represents one case Each column represents one variable First column usually identifier —name, initials, or ID number Can be paper or electronic Can be quickly reviewed and updated

Example of a Line Listing

6. Perform Descriptive Epidemiology After collection of data characterize the outbreak by: Time Place Person

Time (Epidemic curve) Epidemic curve Histogram of the number of cases by their date of onset Visual display of the outbreak’s magnitude and time trend Common source vs. Propagated

Graphical Representation of an Outbreak Classic epi. curve

Place (spot map, shaded map) Geographic extent of problem Clusters or patterns providing important etiologic clues Spot maps Where cases live, work or may have been exposed

Person (Tables) Determine what population at risk Usually define population by host characteristics or exposure Use rates to identify high-risk groups Numerator = number of cases Denominator = number of people at risk

7. Develop Hypotheses Source of the agent Mode of transmission Hypotheses should address Source of the agent Mode of transmission Vector or vehicle Exposure that caused disease

Develop Hypotheses Generating the hypothesis Talk to several case-patients Use open ended questions Ask lots of questions Talk to local health department staff

8. Test Hypotheses Evaluate the credibility of your hypotheses in one of two ways; Compare with established facts When clinical, lab, environmental and/or epi data undoubtedly support hypothesis Use analytic epidemiology to quantify relationships Cohort studies Case control studies

9. Refine hypotheses and do additional studies Epidemiologic When analytical epi unrevealing need to reconsider your hypotheses Go back and gather more information Conduct different studies Laboratory Additional tests

10. Implement Control /Prevention Measures Implement control measures as soon as possible May be aimed at agent, source, or reservoir eliminate the source interrupt transmission reduce susceptibility Create mechanism to evaluate both short and long-term effectiveness of control / prevention measures

11. Communicate Findings Oral briefing for local authorities Local health authorities and persons responsible for implementation of control and prevention measures Written reports; that follows intro, background, methods, results, discussion and recommendations.

Communicate the Findings

References http://www.cdc.gov/ophss/csels/dsepd/ss1978/lesson6/section2.html