Guidance

Toolkit 5: investigation protocol

Published 21 January 2025

This toolkit provides an outline of points to consider in the development of an outbreak investigation protocol. The types of investigation required (for example epidemiological, microbiological, environmental) will depend on the outbreak being investigated.

Title

The title should contain, at a minimum, the type of outbreak, suspected pathogen, or illness, setting or location of outbreak, and date for example. ‘A protocol to investigate a suspected Cryptosporidium outbreak linked to Petting Farm X, August 2024’.

Background

To include:

• information on the organism, including:
  • relevant transmission dynamics, such as incubation period and period of infectiousness, as well as mode of transmission and common sources of infection
  • clinical severity
  • epidemiology in England
• how the outbreak was identified
• summary of outbreak epidemiology to date (for example, number affected, date first cases reported, date and time of onset of first cases and any laboratory confirmation, symptoms, severity, geographical distribution, demographic distribution)
• summary of relevant microbiological, environment, food chain and veterinary findings to date
• implicated premises and setting details (if known)
• the initial response to the outbreak
• previous research where relevant

Aim and objectives of investigation

Aims and objectives may include, for example:

• to describe the outbreak in terms of time, place and person, including determining the size and geographical spread of the outbreak,
• to describe the type and severity of illness
• to identify exposures associated with illness
• to provide evidence to support the actions of the IMT to prevent further illness

Epidemiological investigations

Typically, a protocol will include:

• study design overview (case-control, cohort, cross-sectional, or case series description)
• setting (geography and dates of focus, including periods of recruitment)
• study population inclusion and exclusion criteria
• case definitions
• sample size calculations, if relevant
• data collection/sources including questionnaires and case finding where relevant
• data management
• analyses, including descriptive and statistical, with mention of a-priori considerations and hypotheses as well as metrics to be reported. This section should clearly address the investigation objectives
• bias/confounding considerations
• ethics, such as informed consent and data governance considerations (data storage, sharing, retention)

Microbiological investigations

Describe the characterisation of isolates (human, environmental, animal, or food, noting details for environmental and veterinary investigations may be captured separately in other sections, see below) to distinguish the outbreak strain, or other relevant microbiological investigations, including:

• microbiological/sampling kits used
• process for sample collection and transport
• laboratory testing process (including which laboratory)
• how results are reported
• risks to investigators and participants, if relevant

Environmental investigations

Describe the methods for sampling and analysis of environmental samples taken as part of the investigation. If the outbreak is foodborne, describe the methods for investigating and coordinating the food and feed chain taken as part of the investigation, including;

• describe methods for source tracing of food products
• include existing information held on incidents and signals
• provide clarity on microbiological legal and policy requirements where necessary.

Veterinary investigations

Describe the methods for the microbiological sampling and analysis of animal samples or Food Standard Agency (FSA) approved establishment samples taken as part of the outbreak investigation. Describe operational processes in FSA approved establishments and clarity on roles and remits to aid IMT understanding, where necessary.

Communications

Describe how the results of the investigations will be communicated to stakeholders and, if appropriate, the public. Describe the impact of public communications on the outbreak investigations, where relevant.

Funding

Where relevant

Appendix

This section may include, for example:

• questionnaires used as part of the outbreak investigation
• schematic overview of protocol
• consent form for participants if relevant
• food chain maps