Trends in the Incidence of Culture-Confirmed Human Salmonellosis Reported in Virginia During 2012-2022

Abstract

Recognizing that Salmonella is a leading cause of bacterial foodborne illness in the United States (US), the US government established disease reduction goals for salmonellosis incidence. Surveillance data are used to monitor progress toward these goals, and to characterize salmonellosis epidemiology (e.g., specific serotype causing disease, model national and regional trends in incidence). This study used data from 11,411 culture-confirmed salmonellosis cases among Virginia residents reported to Virginia Department of Health during 2012-2022 to characterize salmonellosis epidemiology in Virginia using incidence rate ratios (IRRs) and a negative binomial Bayesian splines model. Trends were modelled separately for salmonellosis overall and for individual sub-types at the state level. State-level modelled incidence ranged between 10.9-12.9 (per 100,000 people); the lowest and highest reported incidence occurred in 2020 and 2019, respectively. During the COVID-19 pandemic, incidence appears to have decreased; incidence has not returned to pre-pandemic levels. According to the splines model, there was a substantial decrease in state-level culture-confirmed salmonellosis incidence in 2021 compared to 2018, which is consistent with trends nationally. Of the187 total Salmonella serotypes reported in Virginia during 2012-2022, 64% of culture-confirmed cases were attributable to six serotypes: Typhimurium/I 4,[5],12:i:- (20%), Enteritidis (18%), Newport (11%), and Javiana (8%), Bareilly (4%), and Braenderup (4%). The incidence of illnesses to specific attributable serotypes appeared to change between 2012 and 2022 with some serotypes decreasing in incidence (e.g., the incidence of S. Typhimurium/I 4,[5],12:i:-) and others increasing (e.g., S. Braenderup). Opposing serotype-specific trends may be contributing to the apparent stability in overall salmonellosis incidence in Virginia during 2012 through 2022. Some serotypes had an overall high reported incidence across all months, while others had distinct peaks in incidence during summer months (June-August). Similar to national trends, children <4 years old had the highest reported incidence of all age groups across all serotypes, indicating that reducing incidence in this population should be prioritized for achieving the desired reduction in salmonellosis incidence. Analyses using whole genome sequencing data indicated that within each of the 6 most common serotypes, most isolates represented 1-3 subtypes. Overall, our analyses indicate that trends in reported culture-confirmed salmonellosis incidence in Virginia are largely consistent with national trends and support the use of analyses of salmonellosis incidence at the subtype level to inform intervention efforts to address incidence of infections caused by specific serotypes.