In June 2018, WHO convened a working group constituted of 36 experts in epidemiology, clinical medicine, environmental sciences, data management and data sciences who worked in organisations including WHO, the United States Centers for Disease Control (US-CDC), Médecins Sans Frontières (MSF), the European Centre for Disease Prevention and Control (ECDC), the London School of Hygiene & Tropical Medicine (LSHTM), the Helmholtz Centre for Infection Research, and Oxford University. These participants belonged to international organisations involved in field outbreak investigations and were considered experts in working in epidemics in low- and middle-income countries (LMICs). The list of participants was established based on a list of WHO experts in health event investigations, existing working relationships with WHO external partners in data collection, recommendations from experts consulted during recent work for the investigation of outbreaks of unknown origin, and partner institution experts involved in field data collection for all hazards. Terms of references of the working group were circulated and agreed during a first teleconference in June 2018.
The working group was invited to participate in the process of selecting a set of minimum variables (defined as ‘Epi Core Variables’) for event investigations under the WHO-OT project. This process commenced with a review of thirty-one case investigation forms from a range of sources from WHO, US-CDC, MSF, International Federation of Red Cross (IFRC) which had been used in previous health events and included both infectious and non-infectious hazards. From this, the participants selected variables which were common to a generic outbreak situation rather than specific for any pathogen or disease aetiology. These variables, called the “initial list”, contained 82 variables grouped into four categories: 1) Notification interview, 2) Case information, 3) Clinical information and 4) Exposure (Appendix 1). Questions for each variable were phrased in a way that would allow them to be used in any type of health event, whilst also ensuring the data to be comparable across situations. Variables describing clinical signs and symptoms were grouped into two sub-groups including (a) those characterising the severity of any disease and (b) those covering signs and symptoms; Only variables that characterise the severity of any disease, (a), were included in the prioritization exercise.
In order to reach consensus on which of the variables should classified as ‘Epi Core’, the working group decided to use a Delphi process.
Prioritisation of variables was restricted to a sub-group of 26 members of the working group in order to keep a balance among members from different institutions and to restrict the group to experts with regular participation in field outbreak investigations. We conducted the Delphi via an online survey tool in two stages conducted between January 2019 and June 2019 using Enketo web-forms (11). Delphi participants were sent a guidance document for the process which outlined the purpose of the selection of variables. The variables were ordered by categories and accompanied by a description. This allowed the experts to prioritise the importance of including these as ‘Epi Core variables’ as defined in Table 1. For each variable, this sub-group of participants were asked to determine whether the variable should be retained for inclusion, and if so, to assign its priority in data collection during an outbreak as essential, high, medium, low or unknown (Table 1). The priority classification serves to adapt to the resources available in the field at the time of the outbreak investigation, i.e. if resources are limited, the field officer should collect at a minimum the essential variables. Experts could also provide additional explanatory comments in relation to their categorisations.
In January 2019, all 26 members of the sub-group were sent invitations by email to participate in the first round of the Delphi process. Participants were given 55 days to complete the survey. Automated reports of the aggregated results and any additional comments from the first round were generated using R statistical software (version 3.5.3) and were sent to all participants in March 2019, and 25 members of the sub-group were sent invitations to participate in the second round for which the methods were the same. Two additional participants were added to the second round to account for a loss to follow-up of three participants after the first round.
Those variables for which a priority classification reached at least 75% consensus during the first round, were excluded from the second round. In a systematic review of English language Delphi studies, the most common definition for consensus was percentage agreement, with 75% being the median threshold to define consensus (12). Similar to the first round, 75% was used as the threshold for variables to be included in the second round.
Participants were given 26 days to respond before reports of the results from both the first and second round were disseminated. Following this, all participants were invited to a teleconference to discuss the results, in which 13 attended. Given the limited number of variables which reached a consensus of 75% and the large spread of the results, the group decided to broaden consideration of variables which reached a consensus at 60%. Therefore, we also show those variables which reached at least 60% consensus.
The minimum set of variables served to develop a generic data collection form for outbreak investigation, nominally titled the ‘T0 initial case investigation form’ (“T” for time, “0” for first data collection), to collect the minimum set of data to describe an outbreak of any origin and to build initial hypotheses regarding its origin/source, transmission, aetiology or syndrome. Given that not all of the working group had a clinical background, the Delphi process was only used to facilitate the prioritisation of signs of severity of disease. A sub-groups of medical experts then selected pathogen- or syndrome-specific variables from those medical variables included in the initial list of 82 variables (Appendix 1) to be included in the T0 form. WHO laboratory experts were consulted to define variables for laboratory diagnosis to be included in the form.
The T0 form was field tested by members of the National Rapid Response Teams Knowledge Network (RRT KN) in French and English-speaking countries. Feedback was received from three countries, Tunisia, Egypt, Morocco and the Eastern Mediterranean Public Health Network (EMPHNET) who tested the T0 during training of Rapid Response Teams. The field-testing led to the inclusion of additional variables, mainly pertaining to exposure, included in the list as ‘Epi Core’ in the T0 form following the recommendations issued from field practitioners in the testing process. One variable, ‘neighbourhood/camp/settlement’, was deleted following results of the field-testing.
The priority classification and definition of the categorisation of the variables.
Category of prioritisation
Mandatory variables that should appear on all outbreak investigation forms
Variables which are highly desirable however not essential
Variables which are recommended to be collected when feasible. These should be considered when facing an unusual outbreak that triggers the need for more detailed information, e.g. a novel form of a disease, a changing epidemiological pattern of a known disease, or the suspicion of new risk factors.
Other variables which should be collected when feasible in order to refine the analysis