PURPOSE OF THE STUDY.
Pertussis infection remains a major public health problem with reported cases increasing more than 27-fold since 1976. The prevalence of asthma has also increased, with up to 17% of children affected. The purpose of this retrospective study was to determine if patients with asthma were at increased risk of pertussis.
This population-based, case-controlled study compared asthma history in adults and children with documented pertussis (positive polymerase chain reaction [PCR]) to that of matched controls suspected of having pertussis but with negative PCRs.
Pertussis PCRs during a 2-year outbreak in Olmstead County, MN, were used to identify 223 pertussis-positive cases; 164 patients were eligible for inclusion. From a pool of 5537 pertussis-negative patients, 328 age- and sex-matched controls were identified. A previously validated formula was used to estimate the population attributable risk percentage of asthma for pertussis infections.
The rate of pertussis immunization was the same in both groups (65.2% cases versus 68.9% controls, P = .172). Nearly 80% of cases were younger than 18 years old (mean = 13.9 years). Sixty-two (38%) patients with pertussis and 85 (26%) controls had asthma before the date of pertussis testing (odds ratio [OR] 1.83, P = .005). On the basis of the adjusted OR, the population attributable risk percentage of asthma for the risk of pertussis was 17% for all subjects. Antibiotic use and family history of asthma approached, but did not reach, statistical significance between groups. After adjusting for those variables, a history of asthma before the index date of pertussis PCR was still significantly associated with the risk of pertussis (OR 1.73, P = .013). Age stratification analysis showed that the association between asthma and increased risk of pertussis was present only in children and adolescents. The use of oral or inhaled corticosteroids did not affect pertussis risk.
Asthma is associated with an increased risk of pertussis. Given the high incidence of asthma, relatively low pertussis immunization rates, and the increased attributable risk of asthma for pertussis infection, patients with asthma should be a target group for primary pertussis vaccination and for appropriate boosters.
It is possible that altered innate or acquired immunity and/or altered airway epithelium increase the risk of pertussis infection in patients with asthma. The authors were not able to assess asthma control, so they were unable to correlate asthma control with risk of pertussis infection. One can speculate that poorly controlled asthma with greater airway inflammation increases the risk of pertussis (and other airway infections). This study does not change the need to enhance overall immunization rates or the need to monitor and maintain asthma control carefully. It does, however, provide a little more incentive to do both.
- Copyright © 2012 by the American Academy of Pediatrics