A comparison of using online market panel members and traditional methods in control recruitment for a case-control study during a national outbreak of STEC O145, United Kingdom

National foodborne outbreaks of gastrointestinal disease often require rapid case-control investigations to identify the source.Online market panels offer a potential alternative to traditional control recruitment.We compared market panel controls to traditional controls in case-control recruitment during a 2024 UK outbreak of STEC O145.Two case-control studies were conducted for two different control groups a) Salmonella cases as casecontrols and b) online market panel members.Timeliness, cost and resources were compared and a Firth logistic regression compared findings in a control-control analysis.In total, 43 cases of STEC O145, 63 Salmonella case-controls and 93 panel controls were recruited.Neither control group reached the recruitment target for the younger adults age group.Salmonella case-controls had a nine-fold greater staff time to recruit and costed five times more than panel controls (25.82vs 4.99 per control), partially due to intervieweradministered questionnaires compared with self-completion by panel controls.Both analytical approaches identified the same outbreak source, with no significant differences for exposures between the control groups.The cost and resource savings associated with panel controls justifies their use as standard procedure in outbreak investigations.We recommend exploring engagement with age groups that are difficult to recruit and assess alternative strategies to reach them.