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Epidemiol Infect. 2013 Nov;141(11):2346-53. doi: 10.1017/S0950268812002968. Epub 2013 Jan 16.

The serotype case-case design: a direct comparison of a novel methodology with a case-control study in a national Salmonella Enteritidis PT14b outbreak in England and Wales.

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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.

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