[Source: Eurosurveillance, full page: (LINK). Abstract, edited.]
Linked seasonal outbreaks of Salmonella Typhimurium among passerine birds, domestic cats and humans, Sweden, 2009 to 2016
Robert Söderlund 1, Cecilia Jernberg 2, Linda Trönnberg 2, Anna Pääjärvi 2, Erik Ågren 1, Elina Lahti 1
Affiliations: 1 National Veterinary Institute, Uppsala, Sweden; 2 Public Health Agency of Sweden, Solna, Sweden
Correspondence: Robert Söderlund
Citation style for this article: Söderlund Robert, Jernberg Cecilia, Trönnberg Linda, Pääjärvi Anna, Ågren Erik, Lahti Elina. Linked seasonal outbreaks of Salmonella Typhimurium among passerine birds, domestic cats and humans, Sweden, 2009 to 2016. Euro Surveill. 2019;24(34):pii=1900074. https://doi.org/10.2807/1560-7917.ES.2019.24.34.1900074
Received: 24 Jan 2019; Accepted: 29 Apr 2019
In 2016, an outbreak of Salmonella Typhimurium (STm) with multilocus variable-number tandem repeat analysis (MLVA) profiles historically associated with passerine birds (2-[11-15]-[3-4]-NA-212) occurred among passerines, cats and humans in Sweden. Our retrospective observational study investigated the outbreak and revisited historical data from 2009–16 to identify seasonality, phylogeography and other characteristics of this STm variant. Outbreak isolates were analysed by whole-genome single nucleotide polymorphism (SNP) typing. The number of notified cases of passerine-associated STm among passerines, cats and humans per month and county, and their MLVA profiles, were compared to birdwatchers’ counts of passerines. Seasonal trend decomposition and correlation analysis was performed. Outbreak isolates did not cluster by host on SNP level. Passerine-associated STm was seasonal for birds, cats and humans, with a peak in March. Cases and counts of passerines at bird feeders varied between years. The incidence of passerine-associated STm infections in humans was higher in the boreal north compared with the southern and capital regions, consistent with passerine population densities. Seasonal mass migration of passerines appears to cause STm outbreaks among cats certain years in Sweden, most likely via predation on weakened birds. Outbreaks among humans can follow, presumably caused by contact with cats or environmental contamination.
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Keywords: Wild Birds; Salmonellosis; Cats; Human; Sweden.