Antimicrobial resistance among agents of community-associated lower respiratory tract infection in the UK and Ireland: trends from 1999/2000 to 2018/2019

Objectives: The BSAC Respiratory Surveillance Programme examined resistance trends among Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis from patients with community-acquired lower respiratory tract infection (CA-LRTI). Methods: Quotas of isolates were sought per collecting site from 1999/00 to 2018/19; an annual October start date captured winter infection peaks within single years. MIC testing was by BSAC agar dilution. β-Lactamase detection with nitrocefin and pneumococcal serotyping by classical methods or WGS. Results: Resistances were uncommon, except that β-lactamases occurred in c. 20% of H. influenzae from 2012/13 following earlier rises, and in >90% of M. catarrhalis throughout. Only 0.11% (12/10881) of S. pneumoniae were fully resistant to penicillin; co-amoxiclav inhibited 97.8% of 13526 H. influenzae and >99.9% of 6309 M. catarrhalis isolates. Cefotaxime inhibited >99% of all isolates at breakpoint, as did relevant fluoroquinolones in the fewer years tested. Tetracycline inhibited >98% of H. influenzae and M. catarrhalis and 85% of S. pneumoniae. Significant shifts were: (i) fluctuating resistances to tetracyclines, macrolides and penicillin in pneumococci, reflecting serotype replacements; (ii) expansion, from 2012/13, in the proportion of H. influenzae with β-lactamase-independent amoxicillin/co-amoxiclav resistance; and (iii) increasing high-level amoxicillin resistance (MIC > 64 mg/L) among β-lactamase-positive H. influenzae. MIC differentials were seen for cephalosporins between β-lactamase-positive and β-lactamase-negative M. catarrhalis, greatest (512-fold) for ceftaroline. Conclusions: CA-LRTI remains eminently treatable, yet shifts are occurring in the serotypes of S. pneumoniae most associated with resistance and in the nature of amoxicillin resistance in H. influenzae. β-Lactamase-related cephalosporin MIC differentials for M. catarrhalis are striking but their clinical significance remains uncertain.