Increasing Incidence of Salmonella in Australia, 2000-2013

Abstract

Salmonella is a key cause of foodborne gastroenteritis in Australia and case numbers are increasing. We used negative binomial regression to analyze national surveillance data for 2000-2013, for Salmonella Typhimurium and non-Typhimurium Salmonella serovars. We estimated incidence rate ratios adjusted for sex and age to show trends over time. Almost all states and territories had significantly increasing trends of reported infection for S. Typhimurium, with states and territories reporting annual increases as high as 12% (95% confidence interval 10-14%) for S. Typhimurium in the Australian Capital Territory and 6% (95% CI 5-7%) for non-Typhimurium Salmonella in Victoria. S. Typhimurium notification rates were higher than non-Typhimurium Salmonella rates in most age groups in the south eastern states of Australia, while non-Typhimurium rates were higher in most age groups elsewhere. The S. Typhimurium notification rate peaked at 12-23 months of age and the non-Typhimurium Salmonella notification rate peaked at 0-11 months of age. The age-specific pattern of S. Typhimurium cases suggests a foodborne origin, while the age and geographic pattern for non-Typhimurium may indicate that other transmission routes play a key role for these serovars.

Fig 1. Map of Australian States and Territories showing the crude notification rate of salmonellosis for 2013 after excluding cases with missing data on serovar, age, or sex.

Administrative boundaries from the Australian Bureau of Statistics [16].

Fig 2. Crude notification rates (dots) and negative binomial regression margins plot (lines with 95% CI) of S. Typhimurium and non-Typhimurium Salmonella notification rates, Australia 2000–2013.

Fig 3. Salmonella Typhimurium and non-Typhimurium predicted notification rates with 95% CI per 100,000 by age group, Australia, 2000–2013.

Note: the first five age groups are single years to highlight the pattern of Salmonella in young children.

Fig 4. Negative binomial regression margins plot of S. Typhimurium and non-Typhimurium predicted notification rates by state and territory, Australia 2000–2013.