A shipyard outbreak of salmonellosis traced to contaminated fruits and vegetables

A large outbreak of food poisoning occurred in September 1996 and involved at least 116 workers at a shipyard in Jurong. Salmonella weltevreden was isolated from the stool specimens of 24 hospitalised cases and three food handlers, giving a total of 27 bacteriologically confirmed cases (25 symptomatic and two asymptomatic) in this outbreak. Based on a case-control analysis, a number of food items consumed on 23 and 24 September 1996 were implicated in the outbreak, viz. a vegetable dish (P < 0.01), watermelon juice (P < 0.01) and cut watermelon (P < 0.001), papaya (P < 0.001) and pineapple (P < 0.05). The median incubation period was 38 hours and the median duration of illness was two days. Four samples of cut fruits obtained from a food stall at the canteen were found to be positive for Salmonella weltevreden. (The antibiogram of all the strains isolated from food samples and stool cultures was similar, consistent with a common source of infection.) Extensive investigation suggested that contamination may have occurred through unauthorised use of industrial water for washing the fresh produce. Early recognition of the outbreak and prompt implementation of control measures prevented further spread of infection.