Epidemiological and clinical characteristics of macrolide-resistant Bordetella pertussis in southern China: an 8-year retrospective study

Recently, macrolide-resistant Bordetella pertussis (MRBP) had emerged in China. The aim of this study was to evaluate the prevalence and clinical characteristics of MRBP in Shenzhen, southern China. We enrolled patients with culture-confirmed pertussis at Shenzhen Children’s Hospital from January 2016 to December 2023. Demographic and clinical data of the patients were collected. The antimicrobial susceptibility of Bordetella pertussis isolates was evaluated, and the minimum inhibitory concentrations (MICs) against erythromycin, trimethoprim-sulfamethoxazole (TMP-SMZ), levofloxacin, ampicillin, and ceftriaxone were determined using the E-test method. Patients were categorized into macrolide-resistant (MR) and macrolide-sensitive (MS) groups according to the erythromycin susceptibility of their isolates. Group comparisons were performed using the Mann-Whitney U test or chi-square test, as appropriate. Multivariable logistic regression was performed to identify factors independently associated with MRBP infection. A two-sided p < 0.05 was considered statistically significant. A total of 678 patients were enrolled. The MIC90 of erythromycin, TMP-SMZ, levofloxacin, ampicillin, and ceftriaxone was > 256 mg/L, 0.38 mg/L, 0.5 mg/L, 1 mg/L, 0.25 mg/L, respectively. The proportion of MRBP strains significantly increased after early 2020 (44.5% in 2016–2019 vs. 89.1% in 2020–2023, p < 0.001). Compared with the MS group, the MR group was older and had higher diphtheria-tetanus-acellular pertussis (DTaP) vaccination rate, longer hospital stay, longer antibiotic use before culture and during hospitalization, more TMP-SMZ use, and more persistently positive cultures (all p < 0.001). Binary logistic regression including age, study period, and DTaP vaccination status showed that only the study period (2020–2023 vs. 2016–2019) was independently associated with MRBP infection (OR = 9.516, 95% CI 5.738–15.781, p < 0.001). The prevalence of MRBP increased markedly in southern China after the COVID-19 pandemic. TMP-SMZ, levofloxacin, ampicillin, and ceftriaxone remained effective against B. pertussis in vitro. MRBP infection was associated with greater antibiotic exposure, longer hospitalization, TMP-SMZ use, and persistently positive cultures.