Foodworkers as a source for Salmonella: A comprehensive review of the role of infected foodworkers in outbreaks of Salmonella in restaurants of Minnesota

During 1993--1997, Salmonella enterica was the most common foodborne outbreak etiology reported to the Centers for Disease Control and Prevention; 38% of 357 Salmonella outbreaks occurred in commercial food establishments. However, the role of infected foodworkers in Salmonella outbreaks is unclear. The study objective was to characterize restaurant-associated Salmonella outbreaks in Minnesota, and the contribution of infected foodworkers.; Restaurant-associated salmonellosis outbreaks during 1995--2003 (n = 23) were reviewed. The median outbreak duration was 21 days. The median number of culture-confirmed patron-cases per outbreak was seven. The median incubation ranged from 9 hours--6 days. A specific food vehicle was implicated or suspected in 39% of outbreaks. Twelve percent (129/1,033) of foodworkers tested positive for Salmonella, and 53% were reportedly asymptomatic. Among symptomatic foodworkers, the median shedding duration was 30 days, vs. 3 days for asymptomatic foodworkers (p = 0.004). Positive environmental samples were recovered in four of 12 (33%) outbreaks. Outbreaks with positive environmental samples lasted 187 days, vs. 26 days of those without (p = 0.03), did not have an identified vehicle, and had a higher proportion of positive foodworkers (22% vs. 8%).; Salmonella shedding in the stool of foodworkers identified through routine surveillance was quantified. During 1997--2004, 110 culture-confirmed Salmonella foodworker-cases were identified. The median shedding duration (n = 85) was 27 days, but varied by serotype. Twenty (18%) foodworkers were part of outbreaks, including 12 at the restaurants where they worked. The identification of foodworker cases through surveillance often prompted initiation of investigations.; During 1997--2001, six outbreaks were identified in a restaurant chain. Four of five investigated outbreaks were characterized by few patron-cases over prolonged periods (53--517 days). Environmental contamination, infected foodworkers (4%--36%), and lack of identified vehicles were characteristic of four outbreaks. One outbreak associated with eggs had many infected patrons, few infected foodworkers (3%), and no environmental contamination.; Infected foodworkers identified through surveillance should raise a high index of suspicion of an outbreak. Prolonged outbreak durations suggest a persistent reservoir of contamination. Infected foodworkers likely serve as an important source for transmission; therefore, assessment of foodworker infection is essential for controlling restaurant-associated salmonellosis outbreaks.