Pertussis seasonal variation in Vietnam: The evidence from a tertiary hospital

Abstract Introduction: Pertussis is a highly contagious and dangerous respiratory disease that threatens children’s health in many countries, including Vietnam, despite vaccine coverage. From 2015 to 2018, Vietnam experienced an increasing number of pertussis cases. Therefore, this study aimed to investigate the trend and examine the seasonal variations in North Vietnam. Methods: Data were collected from medical records of all under-5-year-old inpatients admitted to the National Children’s Hospital in Hanoi, Vietnam (VNCH) 2015–2018. A descriptive analysis was performed to describe the distribution of incident cases by year and season. Linear multivariable regression was conducted to investigate the association between the incidence of cases and seasonality adjusted by age and vaccination status. Results: We identified 1063 laboratory-confirmed cases during 2015-2018, including 247 (23.2%) severe cases. The number of pertussis cases admitted to VNCH per 1000 hospitalizations was 3.2 in 2015, compared to 1.9, 3.1, and 2.1 in 2016, 2017, and 2018, respectively. Outbreaks occurred biennially; however, there was no significant difference in the number of severe cases over this period. Most cases occurred in the hot season (509 cases, or nearly half of the study population). With the adjustment of the vaccination rate and average age, the risk of pertussis-associated hospitalization in the mild season and the hot season was 21% (95% CI [0.12; 0.3]) and 15% (95% CI [0.05; 0.25]) higher than that in the warm season, respectively. The rate of hospitalizations was high in the mild season (28.9%) and the warm season (30.8%), nearly twice as much as that in the hot season; nevertheless, the death rate was only striking high in the mild season, about 5-6 times as much as those in the other seasons. Conclusion: The pertussis incidence in Northern Vietnam varied between seasons, peaking in the hot season (April-July). However, severe cases and deaths increased in the mild season (December-March). Interventions, for example, communication activities on pertussis and vaccination, are of immense importance in lowering the prevalence of pertussis. In addition, early diagnoses and early warnings performed by health professionals should be encouraged.