News Release

Incidence of pertussis among infants appears to be increasing

Peer-Reviewed Publication

JAMA Network

The number of reported cases of the respiratory illness pertussis among infants increased in the 1990's, according to an article in the December 10 issue of The Journal of the American Medical Association (JAMA).

According to background information in the article, pertussis is characterized by a cough that can last for several weeks. In the prevaccine era, pertussis was a major cause of illness and death among infants and children in the United States, with an average of more than 160,000 cases and more than 5,000 deaths reported annually in the 1920s and 1930s. After the introduction of a pertussis vaccine in the 1940s, reported cases decreased more than 99 percent, reaching approximately 1,000 in 1976. After 1976, the number of reported cases of pertussis progressively increased, despite increasingly high rates of vaccination among infants and children.

Masahiro Tanaka, M.D., M.Sc., of the Centers for Disease Control and Prevention, Atlanta, and colleagues conducted a study to determine the trends and characteristics of reported cases of pertussis among infants younger than 12 months of age in the United States from 1980 to 1999. The researchers used data reported to the National Notifiable Disease Surveillance System of the Centers for Disease Control and Prevention between 1980 and 1999, and detailed case data from the Supplementary Pertussis Surveillance System.

The authors found that the incidence of reported cases of pertussis among infants increased 49 percent in the 1990s compared with the incidence in the 1980s (19,798 vs. 12,550 cases reported; 51.1 cases vs. 34.2 cases per 100,000 infant population, respectively). "Increases in the incidence of cases and the number of deaths among infants during the 1990s primarily were among those aged four months or younger, contrasting with a stable incidence of cases among infants aged five months or older. The proportion of cases confirmed by bacterial culture was higher in the 1990s than in the 1980s (50 percent and 33 percent, respectively); the proportion of hospitalized cases was unchanged (67 percent vs. 68 percent, respectively). Receipt of fewer doses of vaccine was associated with hospitalization, when cases were stratified by age in months."

"The increase in reported cases of pertussis among young infants may have resulted from several factors, including a real increase in disease, increased awareness of pertussis among clinicians, or improved surveillance activities," the authors write. "We believe that the increase of reported cases among infants reflects a real increase in B pertussis disease and is not an artifact from the surveillance system ..."

"The potential strategies for improved pertussis control among infants include both nonvaccine strategies, such as trying to reduce infant exposure or increase prophylaxis through educational efforts, and vaccine strategies, such as accelerated vaccination of infants through changes in the recommended schedule of current pertussis vaccines or the development of improved vaccines," they write. (JAMA. 2003;290:2968-2975. Available post-embargo at jama.com)

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Editor's Note: This analysis was supported by the CDC.


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