Objectives: This study evaluated the microbiological distribution and sensitivity of clinical strains from respiratory samples of inpatients to the antibiotics usually recommended for treatment of lower respiratory tract infection (LRTI).

Methods: Using the French SPARES (Surveillance et Prévention de l'AntibioRésistance en Etablissement de Santé) database, we recorded all respiratory microbiological samples collected in 2022 in 409 hospitals located in all regions of France. The distribution of main bacterial species and their resistance to the most frequently prescribed antibiotics for LRTI were compared by age group (18-64 years, 65-79 years, ≥ 80 years).

Results: Among 48,721 strains, 47.7 % were isolated from patients aged 18-64 years, 37.9 % aged 65-79 years, and 14.4 % aged ≥ 80 years. Enterobacteriaceae (30.1 %, 36.0 % and 35.1 %, respectively) and Pseudomonas aeruginosa (19.0 %, 25.0 % and 27.1 %) were the most prevalent pathogens, especially in older patients. Conversely, Haemophilus influenzae (14.5 %, 10.7 % and 8.7 %) and Streptococcus pneumoniae (8.3 %, 5.6 % and 3.4 %) were rare in older age. Overall antibiotic resistance increased with age across all classes: in increasing order of resistance, levofloxacin (9.2 %, 11.1 % and 13.2 %), piperacillin-tazobactam (14.5 %, 16.8 % and 17.4 %), cefotaxime (27.4 %, 34.3 % and 39.5 %), doxycycline (28.2 %, 37.4 % and 39.5 %), cotrimoxazole (32.1 %, 38.5 % and 40.2 %), and amoxicillin-clavulanate (37.2 %, 46.0 % and 51.4 %, p < 0.05 for all comparisons). More than half of the strains were resistant to amoxicillin and erythromycin.

Conclusions: In this large nationwide database of respiratory samples, older age was associated with a high prevalence of Enterobacteriaceae and P. aeruginosa and beta-lactam resistance, a finding challenging current LRTI probabilistic treatment. Conversely, H. influenzae and S. pneumoniae were rarely observed in patients over 80 years of age.