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Pertussis hospitalization rates highest among infants
New strategies should be exhausted to protect infants.
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Mortality and morbidity associated with pertussis dropped dramatically with the introduction of the pertussis vaccine in the United States during the 1940s. By 1994, coverage for three or more doses of pertussis-containing vaccines reached at least 90% among children aged 19 to 35 months.
Despite this success, however, the number of pertussis cases in infants aged 3 months or younger that were reported to the national passive surveillance system increased between the 1980s and 1990s.
To examine the situation from 1993-2004, Margaret M. Cortese, MD, and colleagues conducted a study that compared results obtained from the national passive surveillance survey with the rates of infant pertussis hospitalizations obtained from databases that did not rely on passive reporting.
Their results were published in Pediatrics this month.
Pertussis hospitalization rates
The researchers compiled annual incidence rates for pertussis hospitalizations from the national Supplemental Pertussis Surveillance System and two hospital discharge databases: the Nationwide Inpatient Sample and the Kids’ Inpatient Database.
Data were included for infants aged between 0 and 11 months who were hospitalized for pertussis between 1993 and 2004.
According to the researchers, infants aged between 1 and 2 months had the highest incidence of pertussis hospitalizations based on data collected from the national Supplemental Pertussis Surveillance System.
Hospitalization rates taken from the Nationwide Inpatient Sample were generally stable for infants aged 2 months or younger between 1993 and 2004 and appeared to decrease among infants aged between 3 and 11 months. The peak rates for infants aged 1 to 2 months occurred in 1993 (305 hospitalizations per 100,000 live births), 1999 (259 per 100,000 live births) and 2004 (292 per 100,000 live births).
Cortese and colleagues reported that their findings were similar or slightly higher for the Kids’ Inpatient database.
“Approximately 2,700 infants aged younger than 1 year were hospitalized with pertussis in 2003. Of these hospitalizations, 86% occurred in infants aged 3 months or younger,” Cortese, medical epidemiologist at the CDC’s National Center for Immunization and Respiratory Diseases, told Infectious Diseases in Children. “Ninety-five percent of infants who required mechanical ventilation and all who died were aged 3 months or younger.”
Hospitalization rates were highest among infants aged 1 month, which is younger than the age that the tetanus-diphtheria-pertussis vaccine is typically recommended.
Methods for improvement
The researchers emphasized that infants should receive their first dose of TDaP as soon as they reach the recommended age and should complete the series on time.
Advisory Committee on Immunization Practices’ recommendations for close contacts of infants and all adolescents and adults aged 65 years and younger to receive TDaP are also important because adherence may help reduce the circulation of Bordetella pertussis, according to Cortese.
“In addition to strategies to reduce infant exposure to B. pertussis, other strategies that should be fully evaluated are passively protecting infants by vaccinating pregnant women and actively immunizing infants early, even before age two months,” she said.
Cortese and colleagues concluded that nationally representative discharge databases have demonstrated usefulness in the monitoring of pertussis-related hospitalizations in infants; therefore, the effect of the new TDaP vaccines on infant pertussis should continue being monitored in adolescents and adults through these databases.
“We expected to find higher hospitalization rates using the discharge databases compared with rates based on the passive reporting system because case reporting requires additional efforts that might not always be completed,” Cortese said. “To monitor the pertussis burden among infants, it is valuable to use data sources that do not rely on reporting efforts.” – by Cara Dickinson
For more information:
- Cortese MM, Baughman AL, Zhang R, et al. Pertussis hospitalizations among infants in the United States, 1993-2004. Pediatrics. In press.