Third Streptococcus pneumoniae disease outbreak involving serotype 4–ST801 in a shipyard, Finland, May to June 2025

Finland experienced three invasive pneumococcal disease (IPD) outbreaks among shipyard workers at the same shipyard, in 2019, 2023 and 2025. During the latest outbreak (30 April-6 June 2025), 13 cases were reported, with six confirmed. All five isolates from blood culture-positive cases were serotype 4 - sequence type 801. These were nearly indistinguishable from three isolates from the 2019 outbreak, nine Finnish IPD surveillance isolates and isolates of a 2019 Norwegian shipyard outbreak. We found an association with welding.