Abstract
BACKGROUND: Streptococcus pneumoniae is a leading cause of morbidity and mortality and poses a significant public health threat globally. This study aimed to characterise changes in serotype distribution, in vitro antimicrobial susceptibility, and the frequency of invasive pneumococcal disease (IPD) in paediatric and adult populations in Argentina during the pre-COVID (2018-2019) and post-COVID (2021-2022) eras. METHODS: We conducted a national laboratory-based surveillance study analysing 1304 S. pneumoniae isolates sourced from Argentina's National Surveillance Program for invasive pneumococcal disease. Isolates were stratified by age and serotype, with antimicrobial susceptibility evaluated where applicable. FINDINGS: A significant decrease in isolates was observed in 2020, followed by a resurgence beginning in 2021, peaking in 2022. The most prevalent serotypes in children (<5 years) over the past five years included 3 (11%; 54/494), 24F (8%; 39/494), 19A (7%; 35/494), 12F (6%; 30/494), and 14/23B (4%; 20/494). In adults (≥18 years), the leading serotypes were 3 (17%; 92/542), 8 (14%; 76/542), 7F (5%; 27/542), 9N (4%; 22/542), and 19A (4%; 22/542). Notably, antimicrobial resistance levels were significant, with children showing higher resistance rates (26% multidrug resistance) compared to adults (8%), Among PCV13 serotypes, 19A was predominantly associated with multidrug resistance, while non-PCV13 serogroup 24 was prevalent among resistant isolates. INTERPRETATION: The fluctuations in serotype circulation, particularly among children under five, suggest evolving dynamics post-COVID-19. Although it remains uncertain if these changes are directly linked to the pandemic or reflect broader trends, the data highlight an urgent need for continued surveillance and potential adaptations in vaccination strategies. FUNDING: No funding was received for this study.