Abstract
Although researchers have described numerous risk factors for salmonellosis and for infection with specific common serotypes, the drivers of Salmonella serotype diversity among human populations remain poorly understood. In this retrospective observational study, we partition records of serotyped non-typhoidal Salmonella isolates from human clinical specimens reported to CDC national surveillance by demographic, geographic and seasonal characteristics and adapt sample-based rarefaction methods from the field of community ecology to study how Salmonella serotype diversity varied within and among these populations in the USA during 1996-2016. We observed substantially higher serotype richness in children <2 years old than in older children and adults and steadily increasing richness with age among older adults. Whereas seasonal and regional variation in serotype diversity was highest among infants and young children, variation by specimen source was highest in adults. Our findings suggest that the risk for infection from uncommon serotypes is associated with host and environmental factors, particularly among infants, young children and older adults. These populations may have a higher proportion of illness acquired through environmental transmission pathways than published source attribution models estimate.
Highlights
Salmonella is a diverse genus of zoonotic bacterial pathogens that cause an estimated 1.2 million human infections, 23 000 hospitalisations and 450 deaths annually in the USA [1]
Of the 815 789 cases and 1191 serotypes reported to Laboratory-based Enteric Disease Surveillance (LEDS) during 1996–2016, we excluded 77 783 (9.5%) cases with unavailable or incomplete serotype data, 31 927 (3.9%) cases and 13 (1.1%) serotypes from five reporting partners who fully serotyped an annual median of
Substantial demographic, geographic and temporal variations in Salmonella serotype diversity suggest that host and environmental factors contribute to the risk of infection from uncommon serotypes
Summary
Salmonella is a diverse genus of zoonotic bacterial pathogens that cause an estimated 1.2 million human infections, 23 000 hospitalisations and 450 deaths annually in the USA [1]. Numerous reservoirs and the capacity for environmental persistence give Salmonella multiple entry points into the human population. Salmonella serotypes may differ in their natural reservoirs, their geographic and seasonal distributions, and their ability to cause human infections [4,5,6]. Over 1300 serotypes have been isolated from cases of human disease and reported to the United States Centers for Disease Control and Prevention (CDC) since national surveillance began in 1963, and >2500 serotypes have been identified globally [7]. Only a small proportion of these serotypes are regularly isolated from human clinical specimens [8]; 39 serotypes comprised >90% of isolates reported to the CDC in 2016 [9]
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