Principles of Outbreak Management

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Soili Larkin & Joshna Mavji Aim

Understand the principles of outbreak management

2 Principles of Outbreak Management Objectives

• Define an outbreak

• Describe the purpose of outbreak management

• Outline the steps involved in the management of an outbreak

• Outline the roles and responsibilities of an Outbreak Control Team in the management of an outbreak

• Apply the learning to an outbreak exercise

3 Principles of Outbreak Management What is an Outbreak?

4 Principles of Outbreak Management What is an Outbreak?

• Two or more linked cases of an illness

• A single case of an unusual or rare infection.

• A greater than expected rate of infection compared with the usual background rate that is expected in that population for that place or time.

• A suspected, anticipated or actual event involving microbial contamination of food or water

5 Principles of Outbreak Management Purpose of Outbreak Management

• Identify and control outbreaks of infection

• Reduce illness and complications

• Inform future prevention strategies

• Evaluate existing prevention strategies

• Address public concern

6 Principles of Outbreak Management Outbreak Management Framework

• Case definition • Microbiological investigation

• Confirm diagnosis in known • Environmental investigation cases • Hypothesis generation • Determine background • Analytic epidemiology incidence of disease • Communications • Case-finding • Control measures • Data collection

• Descriptive epidemiology

7 Principles of Outbreak Management Outbreak Management: Case Definition

Case definition Not always possible to secure laboratory confirmation: • False negatives and positives not uncommon Confirm diagnosis • Samples are not always taken (e.g. diarrhoea) • Appropriate tests may be unavailable (e.g. botulism) Background incidence

Case-finding Conversely, laboratory confirmation sometimes essential: • e.g. legionella, hepatitis A/B/C, VHF Data collection • Possible, probable, confirmed Descriptive epidemiology

Microbiological investigation Components • Time…..based on incubation (if known) Environmental investigation • Place….location of suspected exposure • Person….type of illness Hypothesis generation

Analytic epidemiology Task – Using the components listed above, Communications provide a case definition for an outbreak of

Control Measures Hepatitis A

8 Principles of Outbreak Management Outbreak Management: Confirm Diagnosis

Case definition • To assist in verifying whether an outbreak has occurred Confirm diagnosis • For describing the epidemiology Background incidence

Case-finding • Will involve verifying that cases fit the case definition

Data collection • Use medical records or laboratory reports Descriptive epidemiology

Microbiological investigation

Environmental investigation

Hypothesis generation

Analytic epidemiology

Communications

Control Measures

9 Principles of Outbreak Management Outbreak Management: Background Incidence

Case definition • Some outbreaks defined when rates exceed the Confirm diagnosis background incidence in the community (e.g. Background incidence cryptosporidiosis)

Case-finding • Obtained from local and national surveillance data Data collection

Descriptive epidemiology

Microbiological investigation

Environmental investigation

Hypothesis generation

Analytic epidemiology

Communications

Control Measures

10 Principles of Outbreak Management Outbreak Management: Case Finding

Case definition Initial cases may only make up a small proportion of all cases. Active case finding helps: Confirm diagnosis . Establish the onset (which helps identify source)

Background incidence . Define the extent of the outbreak – minor or major . Identify cases requiring healthcare input Case finding . Identify where control measures are needed Data collection . Provide subjects for epidemiological studies

Descriptive epidemiology . Monitor effectiveness of control measures . Determine when the outbreak can be declared over Microbiological investigation

Environmental investigation Line listing is useful to summarise the information. It usually includes: Hypothesis generation . Demographic information Analytic epidemiology . Clinical information

Communications . Exposure information

Control Measures

11 Principles of Outbreak Management Outbreak Management: Case Finding

Case definition Additional cases can be sought from:

Confirm diagnosis • Statutory notifications

Background incidence • Microbiology laboratory results

Case finding • GPs • Hospitals (A&E, ID Dept, inpatients, outpatients) Data collection • Occupational health - large employers Descriptive epidemiology • School reports of absenteeism and illness Microbiological investigation • Household enquiries Environmental investigation • Media appeals Hypothesis generation • Screening of population subgroups Analytic epidemiology

Communications

Control Measures

12 Principles of Outbreak Management Outbreak Management: Data Collection

Case definition • Data collection should be standardised

Confirm diagnosis • Methods depend on the outbreak and resources available: Background incidence . Detailed questionnaires: face-to-face administration Case finding

Data collection . Mailed questionnaires for self-completion

Descriptive epidemiology . Telephone interviews

Microbiological investigation

Environmental investigation

Hypothesis generation

Analytic epidemiology

Communications

Control Measures

13 Principles of Outbreak Management Outbreak Management: Data Collection

• Data could include, as appropriate, questions about the Case definition following:

Confirm diagnosis • Name, age, sex; • GP details; Background incidence • Occupation; work or school address; Case finding • Illness onset and clinical description;

Data collection • Immunisation history; • Food history; Descriptive epidemiology • Water exposure; Microbiological investigation • Social activity: gardening, social events, social venues; • Sexual contacts; Environmental investigation • Injecting drug use; Hypothesis generation • Close contacts: household, school, workplace;

Analytic epidemiology • Animal contact: pets, farm visits, travel; • Foreign or local travel: vaccines and drug history; departure & Communications return dates, countries visited; places visited; accommodation; source of food and water; activities (work, leisure, trekking, jungle Control Measures excursions, etc.); contact with animals.

14 Principles of Outbreak Management Outbreak Management: Descriptive Epidemiology

Case definition • Defines the outbreak in terms of person, place and time

Confirm diagnosis • Provides clues re:- causative organism Background incidence • Hypothesis generation – source of infection / mode of Case finding transmission Data collection

Descriptive epidemiology • Define extent of the outbreak

Microbiological investigation • Monitor outbreak progress & control measures

Environmental investigation • Helps decide when the outbreak can be declared over Hypothesis generation • Epi Curves are useful to suggest: Analytic epidemiology . Type of exposure Communications . Time of exposure

Control Measures . Possible exposure agent

15 Principles of Outbreak Management Outbreak Management: Descriptive Epidemiology

Case definition Patterns of Spread • Common Source Outbreaks - Cases of disease arise from a single, shared Confirm diagnosis or 'common' source, such as a batch of bad food, industrial pollution or a contaminated water supply. Controlling the source stops the outbreak. Background incidence • Point source outbreak – all cases appear to occur within one incubation period therefore is usually of short duration Case finding • Continuing source outbreak – all cases are exposed to a single noxious Data collection influence but the exposure continues over a longer time so the outbreak persists for longer Descriptive epidemiology • Intermittent outbreak – all cases are exposed to a common source that is not well controlled, so outbreaks recur. Microbiological investigation • Person-to-Person Spread – Disease spreads via person-to-person contact. Controlling the source is no longer sufficient to control the outbreak Environmental investigation • Index case with limited spread / point source with secondary transmission Hypothesis generation – a single index case infects other individuals and cases arise after an incubation period. The outbreak wanes when the infected people no longer transmit infection to other susceptible individuals, usually because of implementation of Analytic epidemiology successful control measures.

Communications • Propagated spread – index case infects other individuals (secondary cases) who, in turn, infect more individuals. Control Measures

16 Principles of Outbreak Management Outbreak Management: Descriptive Epidemiology