Seasonal and climatic influence on respiratory infections in children with cystic fibrosis.

Pseudomonas aeruginosa (Pa) and Methicillin susceptible Staphylococcus aureus (MSSA) are the predominant bacteria found in the airways of people with cystic fibrosis (pwCF), significantly contributing to lung disease progression. While various factors influencing the initial acquisition (IA) of these pathogens are known, the impact of environmental conditions remains understudied. This epidemiological study assessed the risk of MSSA and Pa initial acquisitions in relation to seasonality and climatic zones among 1,184 French pwCF under 18 years old. The age at IA for Pa (Pa-IA) and MSSA (MSSA-IA) was estimated using the Kaplan-Meier method. Seasonality and climatic zones were analysed as risk factors using time-varying Cox regression models. The median age at MSSA-IA was notably earlier (2.0 years) than that at Pa-IA (5.1 years). MSSA-IA occurred increasingly younger in more recent birth cohorts, while the age at Pa-IA remained stable over time. The risk of Pa-IA was consistently higher in all seasons compared with spring, peaking in autumn (HR = 1.53), irrespective of climatic zones. In Oceanic and Continental climates, the highest risk for MSSA-IA was in winter (HRs = 1.45 and 1.20 respectively). In the Mediterranean climate, the risk of MSSA-IA was lower in winter compared to spring (HRs = 0.68 and 0.61 respectively), and the median age at MSSA-IA later than for Pa-IA. This study demonstrates that seasonality and meteorological factors may influence acquisition of MSSA and Pa in pwCF. These findings suggest that environmental factors play a role in pathogen acquisition dynamics in CF and could inform the development of preventive strategies.