High prevalence of erythromycin-resistant Bordetella pertussis in Xi'an, China.

Resistance of Bordetella pertussis, the causative agent of pertussis, to erythromycin is rare. Recently, several Chinese isolates were found to be erythromycin resistant. This study aimed to investigate the occurrence of pertussis in children suffering persistent cough and the prevalence of B. pertussis resistance to erythromycin in Xi'an, China. Three hundred and thirteen patients with suspected pertussis admitted to Xi'an Children's Hospital from January 2012 through to December 2013 were included and their nasopharyngeal (NP) swabs were taken for culture and PCRs (targeting IS481 and ptx-Pr). PCR-based sequencing was used to identify the A2047G mutation of B. pertussis 23S rRNA directly from the NP samples. Sixteen (5.1%) and 168 (53.7%) patients were positive for culture and IS481 PCR. Of the 168 samples positive for IS481 PCR, 122 (72.6%) and 100 (59.5%) were positive for ptx-Pr and 23S rRNA PCRs, respectively. All culture-positive samples were also positive for the three PCRs. Fourteen (87.5%) of the 16 B. pertussis isolates were found to be resistant to erythromycin (MICs>256 mg/L). All the 14 isolates were confirmed to have a homogeneous A2047G mutation of 23S rRNA. Of the 100 samples positive for 23S rRNA PCR, 85 (85.0%) were found to have the A2047G mutation by sequencing. Our results indicate that in Xi'an, China, pertussis remains endemic in young children, and the circulating B. pertussis strains are mostly erythromycin resistant.