Study of the risk factors for severe childhood pertussis based on hospital surveillance data.

We used data collected through the French national hospital-based pertussis surveillance network to investigate the risk factors for severe childhood pertussis and more specifically the impact of the vaccination status. For infants, factors associated with a decreased risk of severe disease (defined as hospitalization in intensive care unit, assisted ventilation or death) were having received the first dose of vaccine, being seen late in the course of the disease and in a local hospital. Data also suggested that protection may increase with the number of doses administered. For older children, factors associated with a decreased risk of severity, measured by the hospitalization, were having received a recent booster injection and identification of the contaminator in the close environment. This study reinforces the need for an early start of the primary course in infants and the administration of booster injections in older children.