Outbreak of Salmonella Thompson in the Netherlands

An ongoing outbreak of salmonellosis due to Salmonella Thompson is affecting the Netherlands. Between 2 August and 19 October 2012, 866 cases were confirmed. Their median age was 44 years (range: 0–95 years), 63% were female and 36% were hospital-ised. A matched case–control study suggested smoked salmon as the vehicle. Salmonella Thompson was confirmed in four of nine batches of smoked salmon from one producer. A recall of all concerned smoked salmon products was executed starting end of September. Public Health and the Environment (RIVM) noticed an increase in the number of Salmonella Thompson cases. Two weeks earlier, there had been four cases, and in week 33 another 11 cases were detected. As normally around four cases of S. Thompson are seen in the Netherlands per year, an outbreak investigation was started. Cases were defined as persons in the Netherlands with S. Thompson cultured from any sample type, confirmed by the RIVM, since August 2012. A semi-struc-tured questionnaire exploring relevant food exposures in the seven days before the onset of symptoms was administered by telephone or face to face, beginning 16 August. Data were obtained relating to food consumption and place of purchase as well as other possible exposures such as contact with pets or a person with diarrhoea. Information regarding clinical symptoms , date of onset of illness and date of hospitalisa-tion were also gathered. A matched case–control study was conducted by sending a similar version of the questionnaire to four controls per case, matched on year of birth, sex and municipality. 866 cases were confirmed with an S. Thompson infection (Figure 1), geographically spread throughout the country. Women (63%) were more often affected than men (37%). The median age of the cases was 44 years (range: 0–95 years). Ten percent of the cases were between 0 and 9 years-old and another 16% were between 10 and 19 years-old. The regional public health services actively approached the first 184 cases, resulting in 111 completed questionnaires (60%). Data on hospitalisation were available for 107 cases of whom 36% were admitted to the hospital. First date of illness was known for 192 cases and ranged between 20 June and 6 October (Figure 2). Cases confirmed later than 1 October (week 39) were not contacted, as the most probable cause of the outbreak had been identified and been made public in the media. Date of onset for these cases is therefore only …