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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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

11. 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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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

18. 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

19. 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

20. Epidemic curve (EPI- CURVE)

21. 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

22. 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

23. 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

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

25. 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

26. 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

27. 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

28. 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

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

30. 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