Pertussis incidence has increased in the United States since 1980, punctuated by outbreaks that involve adults and adolescents. We investigated a community-wide outbreak and studied risk factors among adults to identify prevention and control opportunities.
We analyzed surveillance data, interviewed patients, visited outbreak sites, and conducted a case-control study of risk factors for first-in-household adult infection during a Jackson County, Oregon, outbreak in 2003.
In Jackson County, 135 pertussis cases were reported; the incidence was 71 per 100 000 population compared with 0 to 1 per 100 000 population from 1995 through 2001. Case investigations identified 2658 close contacts (19.7 per case); 1050 (40%) received antibiotic prophylaxis. Older children and adolescents (aged 10-17 years) and adults (aged ≥18 years) accounted for 67% of cases. Five infants were hospitalized (192 hospitalizations per 100 000 infants) compared with 18 in the remainder of the state (33 per 100 000 infants). Many cases occurred among epidemiologically linked clusters of varied composition, such as jail inmates and employees, methamphetamine users, low-income housing residents, school students and employees, and employees in certain work settings. Adult patients were more likely than controls to live with children aged 6 to 10 years (odds ratio, 6.4; 95% confidence interval, 1.8-23.4) and less likely to report a complete childhood vaccination history (odds ratio, 0.1; 95% confidence interval, 0.003-0.9).
The predominance of adolescent and adult cases, appearance of new clusters despite aggressive control efforts, clustering of cases in hard-to-reach populations, and absence of modifiable risk factors for adult disease in this outbreak all suggest that universal booster vaccination of adolescents and adults might offer the only effective means to prevent such events in the future.