Outbreak Toolkit
Providing the tools to investigate disease outbreaks, collect data and guide response activities
WHO’s Rajib Chowdhury speaks with Nurse Akter in the Suhrawardy Hospital dengue ward in Sher-E-Bangla-Nagar, Dhaka, on 3 October 2023.
Case investigation form for outbreaks of unknown cause (T1)
An outbreak of unknown origin is defined as:
- An outbreak of an unknown disease
- An outbreak of a new emerging disease
- An outbreak of a known disease with unusual place of occurrence, or unusual clinical expression, or unusual mode of transmission
More on case investigations of outbreaks of unknown cause
A review of several case studies of investigations of outbreaks of unknown cause showed that priority shall be given to develop case investigation form to collect accurate initial data collection to save time and efforts to rapidly identify the origin of the outbreak. https://pubmed.ncbi.nlm.nih.gov/36630891/ The case investigation form supports the rapid identification of the source, mode of transmission or agent involved in the outbreak.
The analysis of the data collected with the case investigation form enables the
Identification of suspected disease and differential diagnosis with detailed description of signs and symptoms of the cases;
- Identification of the source of the outbreak with comprehensive collection of information about past and present exposures of the cases;
- Identification of the mode of transmission of the outbreak with detailed description of the diffusion/extension in space and time of the outbreak;
By using this form, the investigation team may:
- Rapidly develop a case definition for the event,
- Provide accurate clinical characterisation of cases to identify syndrome and/or disease;
- Elaborate hypotheses regarding source and transmission mode;
- Provide rapid risk assessment of the evolution in time and space; and
- Provide differential diagnosis to guide laboratory investigations in humans, animals, and the environment.
Collect early systematic and verified information from all patients. In the context of investigating an outbreak of unknown disease, the quality of the data collected is key to fasten the resolution of the investigation. Those data must be collected by dedicated health professional.
More about the case investigation for outbreaks of unknown cause
Methods to develop the case investigation form of outbreaks of unknown cause
We collected questions from more than 30 existing case investigation forms covering most of epidemic prone diseases, exposure patterns and sources from MSF, IFRC, WHO. We listed variables using the Infectious Disease Data Observatory (IDDO) names and standards and created a bank with all 462 variables and standards for data collection. Consensus on the structure and content of the case investigation form was reached through several discussions and debate among a technical working group formed of the Health Data Collaborative Group of WHO/HQ, the DHIS2 WHO/HQ group and the IDDO team
Structure the case investigation form
The CIF is composed of 462 variables organized in five categories of variables based on the information included: 1-interview and case information, 2- clinical information, 3- exposure information, 4-laboratory information, and 5- final classification (see figure below) which include 29 sub-categories.
The data dictionary for outbreak investigation is a repository of variables commonly used during investigations.
The clinical variables are grouped per apparatus or functional system (neurological, digestive, cutaneous,…). One disease can involve several systems. This approach was preferred to the syndromic approach to collect data when the disease is not identified. The name and format of the variables follow the categories and subcategories.
The exposure variables are classified to support the investigation of risks related to animal human transmission, to human to human transmission, to food or water intoxication and to environmental hazards that can lead outbreak.
The CIF was translated into French and digitized in Kobo to facilitate its uptake and rapid use. “Gate” questions were inserted in order to tailor the questionnaire to the context and situation. It is adaptable to the needs of the investigation team.
This questionnaire should be used in conjunction with “Public health events of initially unknown etiology: a framework for preparedness and response in the African Region”, 2016 (https://apps.who.int/iris/bitstream/handle/10665/112832/9789290232476.pdf?sequence=1&isAllowed=y
This CIF should be used and filled by a multidisciplinary investigation team including doctor, epidemiologist, laboratory, environmental specialists, veterinarians, and social scientists.