Would You Like a Little Salmonella with Your Sandwich – Sprout Food Safety Research
Would you like a little Salmonella with your sandwich?
Field Epidemiology Training Program
June 1998 Abstracts Health Canada
P Buck, K Grimsrud, J Waters, R Cardinal, J Talbot, C Anand, W Johnson, R Khakhria, J Spika, P Sockett, D Werker
Introduction: By the end of October 1997, 78 cases of infection due to Salmonella Meleagridis (SM), a rare serotype, were reported to the National Enteric Surveillance Program. The province of Alberta, comprising 10% of the Canadian population, reported 43 of these cases. From 1993 to 1995 only 10 isolates of SM had been reported in Canada. In response to the unusual number of cases of SM, we conducted an outbreak investigation in Alberta.
Methods: We defined a confirmed case as a person with laboratory isolation of SM from stool, blood or urine. We conducted home visits on 7 cases to gather detailed food histories and to take food samples. We conducted an unmatched case-control study recruiting recently diagnosed cases and 2 population-based controls per case. We administered, by telephone, a standard questionnaire to cases and controls. We collected retail samples of the suspected produce, examined the distribution pattern of the raw commodity, and investigated production practices. The national reference laboratory performed phage typing.
Results: Food histories collected on SM isolates during 7 home visits revealed 6 cases had consumed alfalfa sprouts. We included 15 cases and 31 controls in the case-control study. We found no differences in the age or sex distribution. Mean ages were 40 years (range: 15-88) and 42 years (range: 18-79) for cases and controls, respectively. Twelve cases (80%) and 19 controls (61%) were female. Eating alfalfa sprouts was strongly associated with illness (OR=22; 95%CI: 3.7-163). SM was isolated from alfalfa sprouts collected from the household of 1 case. Two of 9 retail samples of alfalfa sprouts, all produced by the same Alberta subsidiary of one company, grew SM. The Alberta production plant and the company’s other plants in the provinces of Ontario and Saskatchewan used imported alfalfa seeds from one seed lot. This company marketed “organically grown” produce; alfalfa seeds were not pre-soaked in a chlorine solution prior to sprouting. SM isolates from the 3 provinces were identical by phage-typing.
Discussion: On the advice of public health authorities, the company implemented a voluntary national recall of alfalfa seeds and sprouts from the implicated lot. Further study is required to identify effective and acceptable decontamination procedures which can be used by sprout growers. Rare serotypes have facilitated detection of outbreaks of salmonellosis attributed to alfalfa sprouts in Canada and internationally.