a1 Health Protection Services Colindale, Health Protection Agency, London, UK
Societal and technological changes render traditional study designs less feasible for investigation of outbreaks. We compared results obtained from case-case and case-control designs during the investigation of a Salmonella Enteritidis PT14b (SE14b) outbreak in Britain to provide support for validation of this approach. Exposures of cases were compared to concurrent non-Enteritidis Salmonella cases and population controls recruited through systematic digit phone dialling. Infection with SE14b was associated with eating in oriental restaurants [odds ratio (OR) 35·8, 95% confidence interval (CI) 4·4–290·9] and consuming eggs away from home (OR 13·8, 95% CI 1·5–124·5) in the case-case study and was confirmed through a concurrent case-control study with similar effect estimates and microbiological findings of SE14b in eggs from a specific chicken flock on a Spanish farm. We found that the case-case design was feasible, quick and inexpensive, potentially minimized recall bias and made use of already interviewed cases with subtyping results. This approach has potential for use in future investigations.
(Received May 22 2012)
(Revised October 24 2012)
(Accepted December 03 2012)
(Online publication January 16 2013)
c1 Author for correspondence: Dr D. Zenner, Consultant Epidemiologist, Health Protection Services Colindale, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, UK. (Email: firstname.lastname@example.org)