In people with cystic fibrosis, repeated cycles of airway infection and inflammation are a major driver of declining lung function and structural lung damage. Two bacteria predominate: methicillin-sensitive *Staphylococcus aureus* (MSSA), the most frequently isolated organism in young children, and *Pseudomonas aeruginosa* (Pa), which becomes the dominant pathogen in adulthood. Although several determinants of the initial acquisition of these pathogens are known—demographic characteristics, comorbidities, modifier genes, prior colonizations, smoking, pollution, socioeconomic conditions, and geographic factors—the influence of environmental and climatic conditions remained poorly documented, particularly in Europe and for MSSA, as the existing literature is largely North American and dated.
To address this gap, this epidemiological study assessed the risk of initial acquisition of MSSA and Pa according to seasonality and climate zone in 1,184 French children with cystic fibrosis under 18 years of age. Patients were distributed across three climate zones defined according to the Météo France classification: oceanic (58%), continental (36%), and Mediterranean (6%). In accordance with French recommendations, these children undergo quarterly follow-up at a specialized center, with microbiological analysis of sputum after each visit. Age at initial acquisition was estimated using the Kaplan-Meier method, and seasonality as well as climate zone were analyzed as risk factors using time-dependent Cox models, adjusted for birth cohort. Spring, the season presumed to have the lowest incidence, was used as the reference.
The median age at initial acquisition of MSSA was found to be markedly earlier (2.0 years) than that of Pa (5.1 years). Moreover, MSSA acquisition occurred increasingly early in recent birth cohorts, whereas Pa acquisition remained stable over time. The risk of initial Pa acquisition was higher in all seasons compared with spring, peaking in autumn (hazard ratio, HR = 1.53), regardless of climate zone. For MSSA, the highest risk occurred in winter in oceanic and continental climates (HR = 1.45 and 1.20). In the Mediterranean climate, by contrast, the winter risk of initial MSSA acquisition was lower than in spring (HR = 0.68 and 0.61), and the median age of MSSA acquisition there was later than that of Pa.
This work highlights an influence of seasonality and meteorological factors on the acquisition of MSSA and Pa in children with cystic fibrosis. It suggests that environmental factors contribute to the dynamics of acquisition of these pathogens and could help inform the development of preventive strategies.