Discrepancy between antibiotics administered in acute exacerbations of chronic bronchitis and susceptibility of isolated pathogens in respiratory samples: multicentre study in the primary care setting

A national multicentre prevalence study was undertaken to determine the bacterial strains associated with mild-to-moderate acute exacerbations of chronic bronchitis (AECB) in the primary care setting and the susceptibility of isolated pathogens to different antimicrobials usually prescribed to these patients. All samples were processed by a central reference laboratory. Microdilution tests were carried out to establish the minimum inhibitory concentration (MIC) of various antimicrobials. A double-disk test was performed to establish the macrolide resistance phenotype in Streptococcus pneumoniae. Tests to detect the presence of β-lactamase in Haemophilus influenzae and Moraxella catarrhalis and polymerase chain reaction to detect the presence of ermB and mefA genes in S. pneumoniae isolates were also performed. A total of 1537 patients were included in the trial and 468 microorganisms were isolated from sputum samples, with the most frequent isolates being S. pneumoniae (34.8%), M. catarrhalis (23.9%) and H. influenzae (12.6%). Resistance rates of pneumococci were 47.2% for penicillin, 1.2% for amoxicillin, 34.3% for macrolides (87.5% of which showed high-level resistance), 13.6% for cefuroxime/axetil and 4.2% for levofloxacin. No bacterial isolates showed resistance to telithromycin. Empirical antibiotic treatment was prescribed to 98.3% of patients, including macrolides to 36.6%, amoxicillin with or without clavulanic acid to 32.3% and fluoroquinolones to 16.1%. In conclusion, S. pneumoniae was the most frequently isolated bacteria in patients with mild-to-moderate AECB. Despite the high rates of resistance of pneumococci to macrolides, they continue to be the most widely used antibiotics in primary care to treat AECB.