The National Public Health Agency of Sweden performed a traceback investigation implicating undercooked hamburgers using meat imported from Poland. Salmonella Enteritidis was recovered from samples of ground meat common to eleven of the fifteen patients applying whole genome sequencing. News reports in various media did not indicate the number of the school ski-team exposed so it is not possible to establish the attack rate.
This case confirms the need to cook hamburgers to an internal temperature of 165F for at least 30 seconds to destroy foodborne non spore-forming bacterial pathogens including Salmonella, E.coli and Campylobacter.