Bordetella pertussis Infection in Infants and Young Children in Shanghai, China, 2016-2017: Clinical Features, Genotype Variations of Antigenic Genes and Macrolides Resistance.

Background: The global resurgence of pertussis in countries with high vaccination coverage has been a concern of public health.

Methods: Nasopharyngeal swabs were collected for Bordetella pertussis culture from children with suspected pertussis. Clinical and vaccination information were reviewed through electronic medical chart and immunization record. Antibiotics susceptibility was evaluated using E-test for erythromycin, azithromycin, clarithromycin and sulfamethoxazole/trimethoprim. The MLST genotypes and 7 antigenic genes (ptxP, ptxA, ptxC, Prn, fim3, fim2 and tcfA) of Bordetella pertussis were identified by polymerase chain reaction amplification and sequencing.

Results: During January 2016 to September 2017, a total of 141 children 1-48 months of age were culture-confirmed with pertussis, of whom 98 (69.5%) were younger than 6 months, 25 (17.7%) had completed at least 3 doses of DTaP and 75 (53.2%) had a clear exposure to household members with persistent cough. Fully vaccinated cases manifested milder disease than unvaccinated and not-fully vaccinated cases. All strains were MLST2. High-virulent strains characteristic of ptxP3/prn2/ptxC2 constituted 41.1% (58/141) and were all susceptible to macrolides while low-virulent strains characteristic of ptxP1/prn1/ptxC1 constituted 58.9% (83/141) and 97.6% (81/83), respectively, were highly resistant to macrolides.

Conclusions: Pertussis is resurging among infants and young children in Shanghai, and household transmission is the main exposure pathway. The high-virulent strains harboring ptxP3/prn2/ptxC2 and the macrolide-resistant Bordetella pertussis strains are quite prevalent. These issues impose a public health concern in Shanghai. Our findings are important to modify the DTaP vaccination strategy and the management guideline of pertussis in China.