Two outbreaks of salmonellosis caused by Salmonella indiana. A survey of the European summit outbreak and its consequences

Abstract

This paper discusses the outbreak of salmonellosis caused by Salmonella indiana during the European Summit Conference in Maastricht on 23 and 24 March 1981. It is estimated that 600–700 of the 1000–1200 exposed persons became ill. The cause of the outbreak was probably a salad base which was used in various snacks and cold dishes. Serious errors were made during preparation of this salad base which allowed the S. indiana present in the product to multiply on a large scale (10 7 per gram). The original source of the S. indiana was never established. The economic consequences of the outbreak were considerable. Medical costs were estimated at F1.40 000, costs due to sick leaves between Fl.200 000 and F1.500 000 and economic loss to the catering firm at approximately F1.500 000 (exchange rate 1981: U.S.$1 = Fl.2.33). The time devoted to investigating the outbreak by government authorities was estimated at 150 man-days. On Saturday, 28 March, the company which had supplied the food for the European Summit Conference provided the catering for a family dinner and a cold buffet. As a precaution all the preparations were supervised by an inspector from the Food Inspection Service. In spite of this, 31 people again fell victim to salmonellosis caused by S. indiana. Of 30 food samples taken during preparation of the meals, 5 were positive for S. indiana. The aerobic and Enterobacteriaceae plate counts were however very low ( < 10 4 and < 10 2 per gram, respectively)as were the infective doses, owing to very stringent control of timing and temperature before consumption. An investigation into conditions in the kitchen showed that although it looked clean it was highly contaminated with S. indiana; 16 of the 70 environmental samples taken were positive for S. indiana. Cross contamination was therefore inevitable. It is presumed that the kitchen became contaminated whilst the infected salad base was being prepared and added to various dishes during the European Summit Conference. The serious symptoms displayed by the victims of the Summit outbreak and the low infective doses in the second outbreak suggest that the S. Indiana involved was more virulent than usual for Salmonella.