Evolution of S. pneumoniae serotype distribution in adults with CAP in Switzerland

<bold>Background:</bold> Streptococcus pneumoniae continues to be a frequent pathogen in community-acquired pneumonia (CAP). Following the implementation of vaccines, the pneumococci serotype distribution is evolving. We analyzed the evolution of pneumococcal serotype distribution in CAP patients. <bold>Methods:</bold> Urine samples were collected among patients with radiologically proven CAP in two Swiss study centers between 2016 and 2021. S. pneumoniae serotyping was performed using two serotype-specific urinary antigen detection (ssUAD) assays covering 24 pneumococcal serotypes. <bold>Results:</bold> A total of 198 urine samples of CAP patients (35.4% female, mean age 62.6 years, 98.3% hospitalized, pneumococcal vaccination rate 5.26%) were analyzed, and 29 (14.6%) were positive. The most frequently detected serotypes were serotype 3 (n=11, 37.9%), serotype 8 (n=4, 13.8%) and serotype 11a (n=4, 13.8%). Overall, 58.6% of the identified serotypes corresponded to serotypes covered by the PCV13 vaccine, 6.9% to PCV15, 31% to PCV20, and 3.4% were non-PCV-20 serotypes. Between 2016 and 2019, ssUAD tests were positive in 16.2%. The most common serotypes were serotype 3 (n=11, 44%), serotype 8 (n=4, 16%), and serotypes 6a and 11a (n=2, 8%, respectively). 0% non-PCV20 serotypes were detected. Between 2020 and 2021, ssUAD tests were positive in 6.7%. Serotype 11a was detected in two patients (50%), serotype 1 in one (25%) patient and serotype 9n, a non-PCV-20 serotype, in one (25%) patient. <bold>Discussion:</bold> We observed a diminution of the S. pneumoniae detection rate among CAP patients during the COVID-19 pandemic (2020-2021) compared to the period before. Concurrently, there is a shift towards non-PCV13 serotypes, but most are still covered by PCV20.