Population-based active surveillance of pertussis hospitalization rates in two cities of China.

Purpose: Hospitalization is most common for severe pertussis cases and those with serious complications caused by pertussis. In mainland China, the immunization program consists of primary vaccinations at 3, 4, and 5 months, followed by a booster at 18 months with DTaP. It remains uncertain whether the first dose at 3 months, rather than 6 weeks as WHO recommended, may increase disease burden, as delayed immunization may lead to lagged protection. This study aimed to determine pertussis hospitalization rates by active surveillance in China, shedding light on immunization strategies for better disease control.

Methods: From June 1, 2021, to May 31, 2022, two Chinese cities underwent a population-based active surveillance. Suspected pertussis cases were confirmed as pertussis cases through PCR and culture. Pertussis hospitalization rates were calculated by dividing the number of laboratory confirmed pertussis cases by the hospitalization coverage rate of surveillance hospitals and the resident population.

Results: During the study period 2021-2022, pertussis hospitalization rate in Yiwu was 2.50/100,000 (95% CrI 2.48-2.53), while in Yongcheng, it was 7.90/100,000 (95% CrI 7.81-8.00). In both cities, infants aged < 1 year had the highest hospitalization rate (215.64/100,000: Yiwu; 217.65/100,000: Yongcheng), followed by the age group of 4-5 years (16.37/100,000: Yiwu; 65.70/100,000: Yongcheng).

Conclusions: This study revealed significant pertussis hospitalization rates in China, particularly among infants aged < 1 year, highlighting the need of timely and early immunization. The higher hospitalization rates in the 4-5-year age group emphasize the importance of targeted preventive measures for preschool children to mitigate the impact of pertussis.