Infant and maternal risk factors for pertussis-related infant mortality in the United States, 1999 to 2004.

BACKGROUND: Infants aged <12 months have the highest rates of complications and death from pertussis of any age group. Factors that increase the risk of pertussis-related death in infants are not well defined.
METHODS: The US Multiple Cause-of-Death and Linked Birth/Infant Death databases were used for 1999 to 2004 to examine pertussis-related infant mortality rates and to obtain anonymous records of infants with pertussis listed as a cause of death and of surviving infants. Infant and maternal characteristics present at the time of birth for infants who died with pertussis were compared with those of surviving infants.
RESULTS: During 1999 to 2004, 91 infant deaths were reported with pertussis as a cause of death. All infants were 7 months or younger; 58% were age <2 months. The average annual infant mortality rate attributed to pertussis was 3.8 (95% CI: 3.0-4.6) per 1,000,000 live births, and 13.1 (95% CI: 9.8-17.1) per 1,000,000 live births for infants aged <2 months. Infant pertussis deaths showed an independent association with birth weight <2500 g, female sex, Apgar score <8, and mother with <12 years education. The mortality rate among Hispanic infants aged <2 months was 2.6 times greater than among non-Hispanic infants of similar age.
CONCLUSIONS: Ensuring pertussis booster vaccination of adults and adolescents in close contact with an infant is warranted to prevent transmission of pertussis to vulnerable infants, particularly infants too young to be immunized. Special emphasis should be given to women and infant settings in which the risk of infant pertussis death might be increased.