Key data for outbreak evaluation: building on the Ebola experience

Cori, Anne; Donnelly, Christl A.; Dorigatti, Ilaria; Ferguson, Neil M.; Fraser, Christophe; Garske, Tini; Jombart, Thibaut; Nedjati-Gilani, Gemma; Nouvellet, Pierre; Riley, Steven; Van Kerkhove, Maria D.; Mills, Harriet L.; Blake, Isobel M.

Simple analyses can be performed solely using incidence time series, from surveillance designed to capture aggregate case counts. However, individual case reports provide much richer information, essential to estimate many of the key parameters outlined above (e.g. characterization of delay distributions). Such data are typically stored in a case database or 'line-list'a table with one line containing individual data for each case. The more data recorded on each case, the more detailed the analyses can be. In the Ebola epidemic, demographic characteristics, spatial location, laboratory results and clinical details such as symptoms, hospitalization status, treatment and outcome, and dates associated with these were reported for at least a subset of cases. The appropriate information to collect may vary depending on the disease: for Ebola, dates of isolation and funeral were relevant. Comprehensive demographic information can be used to determine risk factors for transmission or severity of infection and to project case numbers stratified by demographic characteristics. Detailed information also helps to identify and merge any duplicate entries in a line-list, which may occur when the same person visits multiple health centres over the course of illness, for instance. Finally, information on how each case was detected-for example, through hospitalization, or via contact tracing-can aid assessment of how representative the data are and allow subsequent adjustment for bias [28] ; however, this was not available for Ebola.