The clinical and epidemiological characteristics of pertussis in children and antimicrobial resistance patterns of Bordetella pertussis in Shanghai in 2024

Objective To analyze the epidemiology and clinical characteristics of pertussis, and antimicrobial resistance patterns of Bordetella pertussis in Shanghai in 2024 among children.Methods Demographic information was prospectively collected from pertussis cases confirmed by nucleic acid testing at the Children's Hospital of Fudan University in 2024. Clinical data from all 306 hospitalized cases and 1799 outpatient cases during the peak epidemic period were collected in 2024. Descriptive analyses were performed on the annual epidemic trend, clinical features and vaccination status of hospitalized and outpatient cases. Bordetella pertussis was isolated from nasopharyngeal swab specimens of some cases and antimicrobial susceptibility was tested.Results Among 9899 cases, 5272 were male and 4627 were female. The peak epidemic season occurred from April to July. Children aged 4~10 years accounted for 7744 cases (78.23%). Among 6947 cases with available vaccination records, 6676 (96.10%) had completed the full course of pertussis vaccination. A total of 306 cases (3.09%) required hospitalization, and hospitalization rates were highest among infants aged 0~2 months at 64.8% (83/128). 196 (64.05%) had complications, including 187 (61.11%) with pneumonia/lung consolidation, 7 (2.3%) with pulmonary hypertension, and 1 (0.3%) with encephalopathy. Concurrent detection of other respiratory pathogens occurred in 216 cases (70.6%). The average hospital stay was 3.5 (2.5, 5.5) days and the average hospitalization costs was RMB 8351.6 (6934.6,12086.4) among hospitalized cases. There were 14 severe cases (4.6%), 10 received invasive mechanical ventilation, 1 underwent exchange transfusion, and 1 received extracorporeal membrane oxygenation (ECMO); 2 cases died. Twelve severe cases (85.71%) were unvaccinated, of which 9 (64.3%) were infants aged 0~2 months. The average hospital stay for severe cases was 26.8 (14.1, 50.3) days, with average costs of RMB 66147.4 (42066.9,133530.9). Among the 1799 outpatient and 306 hospitalized cases, paroxysmal cough was present in 1334 (74.4%) and 290 (94.8%), characteristic whoop in 250 (14.1%) and 107 (35.0%), post-tussive vomiting in 532 (29.9%) and 104 (34.0%), cyanosis in 30 (1.7%) and 74 (24.2%), apnea in 24 (1.4%) and 66 (21.6%), and fever in 418 (23.5%) and 137 (44.8%), respectively. Based on minimum inhibitory concentration (MIC) testing of 166 Bordetella pertussis isolates, 165 (99.40%) exhibited high-level resistance to azithromycin (MIC >256 mg/L). The isolates remained susceptible in vitro to trimethoprim-sulfamethoxazole, levofloxacin, ceftazidime, cefoperazone-sulbactam, and doxycycline.Conclusion Children aged 4~10 years were the primary affected group during the 2024 pertussis outbreak in Shanghai. Unvaccinated infants under 2 months of age were at high risk for severe disease. Timely completion of the pertussis vaccination remains a crucial and effective strategy for preventing infant pertussis. There is an urgent need to implement pertussis booster vaccination for preschool-aged children. Empirical use of macrolides for pertussis treatment is not recommended.