Long-term Dynamics and Nasopharyngeal Carriage of Pneumococcal Serotypes, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus From 2013 to 2024 in Healthy French Children

BACKGROUND: Nasopharyngeal carriage of major respiratory bacterial pathogens plays a key role in respiratory infections and transmission. While most carriage studies focus on preschool children, data beyond the age of 6 years remain scarce. This 11-year multicenter study provides a unique overview of carriage dynamics in children up to 15 years old during the Pneumococcal Conjugate Vaccine 13-valent (PCV13) era. METHODS: Nasopharyngeal swabs (2013-2024) from 6420 healthy children aged 6 months to 15 years were collected by 87 pediatricians across France. Standard culture identified Streptococcus pneumoniae (Sp), Haemophilus influenzae (Hi), Moraxella catarrhalis (Mc) and Staphylococcus aureus (Sa); pneumococci were serotyped by latex agglutination, and age-specific carriage patterns were analyzed by cross-sectional comparison. RESULTS: Overall pneumococcal carriage was 28.6%, remaining high up to 5 years of age (≈38%) before declining to ~10% in older children. Non-PCV13 serotypes predominated (23B, 11A, 23A, 15B and 35B), but PCV13 serotypes persisted in 10.4% of pneumococcal carriers and 2.9% of children. Serotypes 19A and 19F remained stable across ages, whereas serotype 3 markedly increased, becoming one of the most prevalent in older children. Hi and Mc carriage mirrored pneumococcus patterns in early childhood but declined with age, while Sa carriage rose inversely. Co-carriage of Sp with Hi or Mc was frequent but rare with Sa, independent of age. CONCLUSIONS: Sp, Hi and Mc carriage remains high up to 5 years of age and declines quickly afterward, whereas Sa shows an inverse pattern. The persistence of serotypes 19A, 19F and the increasing prevalence of serotype 3 in older children may act as a reservoir fueling invasive pneumococcal infections in adults, underscoring the need for continued surveillance and next-generation vaccine strategies.