Outbreak of a new Salmonella phage type in South West England: alternative epidemiological investigations are needed.

An outbreak of Salmonella Typhimurium DT193a occurred in South West England in April-May 2003. Preliminary investigation suggested an association with the consumption of ham. A matched case-control study was implemented, together with an environmental investigation and a geographic information system (GIS) analysis. Thirty-seven cases and 38 controls were enrolled in the study. Matched analysis was based only on 23 cases, as the other cases did not nominate controls. Eighty per cent of cases and 51% of controls had eaten ham (odds ratio = 3.5, p = 0.03). Cases did not differ from controls in terms of distance from outlets providing ham. All environmental samples collected were negative. The epidemiological evidence indicated an association between this outbreak and consumption of ham, but the environmental investigation was inconclusive. Alternative methods should be considered in support of traditional epidemiological investigation.