[Epidemiological and clinical characteristics of pertussis in children at a tertiary pediatric hospital in Shanghai City in 2024].

Objective

To analyze the epidemiological and clinical characteristics of pertussis in children diagnosed at the Affiliated Children's Hospital of Fudan University in Shanghai in 2024, as well as the antimicrobial resistance patterns of Bordetella pertussis.

Methods

Demographic information and vaccination status were collected from the pertussis cases confirmed by nucleic acid testing at the Children's Hospital of Fudan University in 2024. Clinical data from all hospitalized pertussis cases and a portion of outpatient pertussis cases were collected to analyze their clinical characteristics. Bordetella pertussis was isolated from nasopharyngeal swab specimens of some cases, and antimicrobial susceptibility was tested.

Results

Among the 9 899 cases diagnosed in 2024, 5 272 were males and 4 627 were females. The peak epidemic season occurred from April to July. Children aged 4-10 years accounted for 7 744 cases (78.2%). Among 6 947 cases with available vaccination records, 6 676 (96.1%) had completed the full course of pertussis vaccination. A total of 2 085 pertussis patients were included for analysis of clinical characteristics, including 1 779 outpatient cases and all 306 hospitalized cases. The incidence rates of paroxysmal cough, whoop, cyanosis, apnea, fever, and white blood cell counts ≥20×10⁹/L in hospitalized patients were 94.8%, 35.0%, 24.2%, 21.6%, 44.8%, and 26.1%, respectively, all significantly higher than those in outpatient cases (75.0%, 14.6%, 1.7%, 1.3%, 23.5%, and 4.0%; all P<0.001). The proportions of complications and co-infections in hospitalized patients were 64.1% and 70.6%, respectively, also significantly higher than those in outpatient cases (19.3% and 13.8%; both P<0.001). Among both outpatient and hospitalized patients, infants under 7 months were more prone to whoop, cyanosis, apnea, post-tussive vomiting, and peripheral white blood cell counts≥20×10⁹/L compared to those older than 7 months, with statistical significance (all P<0.001). The hospitalization rates were highest among infants aged 0~2 months at 64.8% (83/128). The median length of hospital stay [M (Q1, Q3)] was 3.5 (2.5, 5.5) days, and the median hospitalization cost [M (Q1, Q3)] was RMB 8 351.6 (6 934.6, 12 086.4) among hospitalized cases. There were 14 severe cases (4.6 %), including 2 deaths. Twelve severe cases were unvaccinated, of which 9 were infants aged 0~2 months. The average length of hospital stay for severe cases was (30.7±17.7) days, with a median average cost [M (Q1, Q3)] of RMB 107 996.2 (42 066.9, 133 530.9). Based on minimum inhibitory concentration (MIC) testing of 166 Bordetella pertussis isolates, 165 (99.4%) exhibited high-level resistance to azithromycin (MIC>256.000 μg/ml). The isolates remained susceptible in vitro to trimethoprim-sulfamethoxazole, levofloxacin, ceftazidime, cefoperazone-sulbactam, and doxycycline.

Conclusion

Children aged 4-10 years are the primary affected group during the 2024 pertussis outbreak in Shanghai. Unvaccinated infants under 2 months of age are at high risk for severe disease. Empirical use of macrolides for pertussis treatment is not recommended.