Declaring the end of an enteric illness outbreak is an important step in the investigation. A specific end date helps assess and communicate risk to the public, re-assign resources, as well as remove temporary mitigation measures.
Further information on declaring the end of enteric illness outbreaks is available here.
Three criteria were developed to guide the decision to declare the end of an enteric illness outbreak. This involves determining that illnesses have returned to baseline levels (criterion 1), identifying the last time that individuals may have been exposed to the outbreak source (criterion 2), and allowing enough time to pass to allow these individuals to become ill and be reported to public health authorities (criterion 3).
Identify the date that the outbreak could be declared over using the following steps.
- Identify the expected baseline levels as defined by the outbreak case definition.
- Identify the last date that individuals may have been exposed to the outbreak source.
- Identify the length of time required to allow individuals to become ill and be reported to public health authorities, and add this to the last date that an individual may have been exposed to the outbreak source to obtain the date the outbreak could be declared over. This length of time is the maximum incubation period for Salmonella + the 90th percentile of the reporting delay. Use the line list (Module 4 – Line list) to obtain the reporting delay estimate.