EPIDEMIOLOGY BSPH-122 OUTBREAK INVESTIGATION and response Mpundu KCM MSc Epi and Biostas, BSc Nursing, RM, RN

Overview of disease outbreak An epidemic a localised increase in the incidence of a disease, e.g. in a village, town, or closed institution “Outbreak” can actually be used interchangeably with epidemic and is often preferable because it is a less frightening term in many situations

Objectives of outbreak investigation To control the outbreak Outbreak investigation Response To prevent future outbreaks To strengthen surveillance at local level To provide statutorily mandated service To advance knowledge about the disease To provide training opportunities

Investigation requires Medical and/or public health knowledge Basic concepts of Epidemiology Sources of specialized information (e.g reference books and/or disease specialists) Laboratory testing (but not always) Knowledge of the environment Administration and logistic support

Reasons for investigating outbreaks Outbreak control is of paramount importance To halt the outbreak and prevent further illness To prevent further outbreaks from the immediate source To prevent further outbreaks from other similar sources To address public concerns

Reasons for investigating outbreaks To involve the public in disease control To reduce direct and indirect costs To identify new mechanisms of transmission of known illnesses To identify new or emerging disease agents To satisfy legal and international obligation

Trigger events Warning Signals of an outbreak Clustering of cases/deaths in time/space Unusual increase in cases/deaths Shift in age distribution of cases High vector density Acute hemorrhagic fever or acute fever with renal involvement/altered sensorium Severe dehydration following diarrhoea in patients above 5 years age Unusual isolate

Diseases requiring investigations Endemic diseases with epidemic potential malaria, cholera, measles, hepatitis, typhoid Even a single case of diseases for which eradication/elimination goals have been set e.g. polio Rare but internationally important diseases with high case fatality rates e.g. yellow fever, Ebola Outbreaks of unknown aetiology

Types of epidemic Point (common) source epidemic Propagated epidemic In point source epidemic there is a single common exposure in which a large population is exposed for a short period of time. Propagated epidemic may spread and involves multiple sources (carriers or vectors) and cases occur over prolonged period of time.

Management / Investigation steps Prepare for field work Verify the diagnosis Establish existence of an epidemic Identify and count cases Data analysis: time, place and person Formulate and test hypothesis Assess the local response capacity Set up immediate control measures Address the resource gaps Report writing Dissemination of findings Intensify surveillance

1. Prepare for field work Assemble a team (Rapid Response Team) Assemble relevant supplies and equipment (transport media, specimen bottles, IEC, treatment guidelines, medical supplies, transport, communication means, investigation and surveillance forms, funds, fuel, etc) Alert relevant authorities

Preparing to leave Consult colleagues (microbiologist, vetenary Review literature Decide who will lead the team Identify who provides support in the head office and at the station (Health facility) One page summary of planned activities before leaving Have clear objectives of the investigation! Arrange initial meeting for your arrival

Carry your ‘epi-pac” Log book, forms Files: templates, standard questionnaires Handbooks, relevant articles Camera Personal Protective Equipment (Laboratory equipment) Telephone list: Contact persons Maps

2. Establish existence of an epidemic Verify that the purported outbreak is indeed an outbreak Compare observed incidence with expected No seasonality: compare with incidence from previous weeks/ months Seasonality: compare incidence from similar periods of earlier years. Use threshold levels.

3. Verify the diagnosis Review clinical findings / CASE DEFINITION. Laboratory test findings should be consistent with the clinical and epidemiologic findings Choose a working case definition: who is a case and who is not (by person, place, time). Case definition should be highly sensitive. Talk with health workers in the area Interview and examine patients with the disease Laboratory testing

4. Establishing a case definition Identify and count cases Using the working case definition. Collect information on cases (deaths) and LINELIST Persons who meet the case definition should be “line-listed”. Identify the population at risk or the exposed persons, places where the cases live, work, have traveled to and the possible exposures that might have lead to the disease. Active surveillance/case finding Reinforce passive surveillance

Identify and count cases A case definition will include all actual cases A case must have a laboratory confirmation e.g. an outbreak of bloody diarrhoea Definite case (Confirmed) Isolation of salmonella typhus from stool culture Probable case Bloody diarrhoea with the same person, place and time Possible Case Abdominal cramps and diarrhoea at least three stools in 24 hour period

The laboratory in outbreak investigations Outbreak detection Confirmation of the diagnosis Detection of a new pathogen Details of the pathogen e.g., Serotypes Detection of antimicrobial resistance

5. Data analysis Time (histograms -epidemic curve) graphs) Describe the outbreak by Person, Place, Time (performing a descriptive epidemiology) Time (histograms -epidemic curve) graphs) Draw an Epidemic curve which provides information about magnitude and time trend of the epidemic Epi curve gives information on current and future course of the epidemic, may deduce the probable time of exposure and incubation period Draw inferences about epidemic pattern whether common source, propagated or mixed

Epidemic curve (EPI- CURVE)

5. DATA ANALYSIS Place (spot maps) Provide information on the geographical extent of the problem Clusters or patterns important to etiological clues Draw a spot map illustrating where cases live, work or may have been exposed Indicate where health care facilities Indicate areas of concentration of cases

5. Data analysis Person (tables, bar charts, pie charts) Describe who is the population at risk by demographic characteristics such age, sex, drugs, vaccination status, drugs, occupation etc. Exposure: occupation, environment These characteristics influence the susceptibility to disease and exposure

5. Data analysis After describing the outbreak by time, place and person, summarise what you know Get the population size at risk. Calculate Attack Rate Case Fatality Rate/Ratio Assess quality of case management

Evaluate information Person Place Time Transmission ? Source ? Cases Person Place Time Evaluate information Transmission ? Source ? Pathogen ?

6. Formulate and test hypothesis Hypothesis (or hypotheses) should address Source of the agent. Mode of transmission. Exposures (risk factors). Where resources are available and cause not obvious, compare cases with controls in respect to exposure

7. Assess the local response capacity Staff: number and type available Logistics : drugs/ medical supplies/ guidelines/transport Local response activities Identify gaps to be addressed

8 Implement control measures Interrupt transmission May occur at any time during the outbreak!! Control the source of the pathogen Interrupt transmission Modify host response Prevent recurrence

Control and prevention measures Initiate reasonable control measures as soon as possible Case management, chemoprophylaxis, vaccination ,prevention of nosocomial transmission, and health education Do NOT delay control measures in order to investigate the cause of the outbreak Continue control measures while investigating the possible cause

9. Address the resource gaps Laboratory support Environmental sanitation (involve partners) Public information Specific needs Personnel Drugs, vaccines and equipment Transport, communication and logistics

10. Report writing Written report purposes Action (control and prevention) Record of performance Medical/Legal issues Enhances quality of the investigation Describe the situation Describe the factors that led to the outbreak Evaluate the control measures Give recommendations for prevention of similar outbreak in future