International outbreak of Salmonella Newport, as at 31 January 2012

Salmonella Newport is consistently reported as one of the top six most frequently isolated serovars of Salmonella enterica in England and Wales. Between 2000 and 2010, an average of 223 cases were reported per annum (range 124 – 662), the maximum being reported in 2004 following a national outbreak attributed to the consumption of lettuce at restaurants and takeaways.

In November 2011, as part of a local food survey, the HPA Food Water and Environment (FWE) Laboratory in Preston isolated salmonella from a ready to eat sliced water melon fan. The HPA Laboratory of Gastrointestinal Pathogens (LGP) subsequently confirmed the strain to be Salmonella Newport. Pulse Field Gel Electrophoresis (PFGE) was used to characterise the incident strain. Scrutiny of the international molecular databases confirmed that the PFGE profile of the incident strain had not been reported before.

In late December 2011, Health Protection Scotland reported four cases of S. Newport, all young children. Pulse Field Gel Electrophoresis analysis showed that the strains isolated from these cases conformed to the profile that had recently been identified in the watermelon isolate. The LGP conducted PFGE analyses on clinical isolates referred to the reference laboratory from December onwards. To date 30 cases with the outbreak strain have been identified in England, Wales and Northern Ireland. Exchange of data with reference centres in Europe has shown that cases with the incident strain are also being identified in Germany and the Republic of Ireland. To date colleagues from the Robert Koch Institute (RKI) and the Health Protection Surveillance Centre have confirmed 15 and four cases of infection attributable to the incident strain and in Germany and the Republic of Ireland respectively.

An outbreak control team (OCT) meeting was convened on 16th January with membership from Health Protection Scotland, HPA, Public Health Wales, and the FSA in attendance. A teleconference including colleagues from RKI was held on 19th January. The OCT agreed case definition for a confirmed case is: a person with abdominal symptoms (diarrhoea and/or vomiting), with a laboratory confirmed isolate of S. Newport exhibiting the outbreak PFGE profile. Epidemiological investigations are being coordinated by the Department of Gastrointestinal, Emerging and Zoonotic Infections. These involve assembling the descriptive epidemiology of the outbreak and interviewing reported cases with a bespoke hypothesis generating questionnaire. To date the standard questionnaire has been administered by telephone to 15 cases in England conforming to the case definition. Ten of the cases interviewed to date have confirmed consumption of watermelon in the three days prior to the onset of their symptoms.

Last reviewed: 2 February 2012