A multi-jurisdiction outbreak of Salmonella Typhimurium phage type 135 associated with purchasing chicken meat from a supermarket chain

A multi-jurisdiction case control study was conducted after an increase of Salmonella Typhimurium phage type 135 notifications (a local designated subgroup) was observed throughout Australia. Hypothesis generating interviews conducted in three jurisdictions identified consumption of chicken, eggs, beef and bagged carrots as common among cases and that a high proportion of cases (> 80%) reported purchasing their groceries from a particular supermarket chain (Supermarket A). We conducted a case control study to test whether S. Typhimurium 135 infections were associated with these food items and the purchasing of these products from Supermarket A. The study comprised 61 cases and 173 controls. Cases were younger than controls (p = 0.003) and their distribution by jurisdiction was also significantly different (p < 0.001). In multivariate analysis, cases had significantly higher odds of having eaten chicken purchased from Supermarket A (OR = 3.2, 95% CI 1.2,9.0) or having eaten chicken from a fast food outlet (OR = 2.8, 95% CI 1.0,7.7) compared to controls. Two positive S. Typhimurium 135 results were obtained through a chicken sampling survey conducted at four Supermarket A stores in Victoria. The results of this study were presented to industry and retail representatives, which facilitated better communication between these groups.