Investigation of bacteremia caused by LA S. aureus CC398 in Denmark

Researchers analyzed cases of livestock-associated Staphylococcus aureus (LA S. aureus) bacteremia in Denmark from January 1, 2007, to December 31, 2023. It was found that two-thirds of such bloodstream infections were caused by methicillin-susceptible isolates (LA-MSSA CC398), while methicillin-resistant strains (LA-MRSA CC398) accounted for 34.5% of cases. The first case of bacteremia caused by LA-MRSA CC398 was recorded in 2010, whereas LA-MSSA CC398 isolates occurred sporadically throughout the entire study period.

Overall, over the years of monitoring, livestock isolates caused 0.60% of all S. aureus bacteremia cases in the country. At the same time, the number of such infections is directly related to the scale of industrial pig farming in various regions of Denmark (r = 0.97), while no correlation with the human population size was found. Data analysis showed that the risk of mortality in patients with such infections is comparable to that for strains of human origin.

Scientists note that pigs act as a source of zoonotic transmission of bacteria to farmers with further spread among the population. Signs of adaptation to humans were found in 17% of the studied isolates. The obtained results emphasize the importance of accounting for methicillin-susceptible strains when assessing the actual prevalence of such infections and the need for systematic monitoring of pathogen transmission between livestock animals and humans.