Impact of maternal postpartum tetanus and diphtheria toxoids and acellular pertussis immunization on infant pertussis infection.

BACKGROUND: Mothers often are the source of pertussis illness in young infants. The Centers for Disease Control and Prevention recommend tetanus and diphtheria toxoids and acellular pertussis (Tdap) vaccine for postpartum women before hospital discharge. In January 2008, this recommendation was implemented in a predominantly Hispanic, medically underserved population at Ben Taub General Hospital (BTGH) in Houston (hereafter the intervention population).
METHODS: A cross-sectional study compared preintervention (July 2000 through December 2007) and postintervention (January 2008 through May 2009) periods. Pertussis diagnosis was determined using International Classification of Diseases, Ninth Revision (ICD-9) codes and microbiology reports from 4 major children's hospitals in Houston. Only those infants ≤6 months of age with laboratory-confirmed pertussis illness were included. The proportions of pertussis-infected infants born at BTGH in the pre- and postintervention periods were compared.
RESULTS: Of 514 infants with pertussis, 378 (73.5%) were identified during preintervention and 136 (26.5%) during postintervention years. These groups were similar in age (mean, 79.3 vs 72 days; P = .08), sex (males, 55% vs 52%; P = .48), length of hospitalization (mean, 9.7 vs 10.7 days; P = .62), mortality (2 deaths each; P = .29) and hospital of pertussis diagnosis. After adjustment for age, sex, and ethnicity, the proportions of pertussis-infected infants born at BTGH and potentially protected through maternal postpartum Tdap immunization were similar for the 2 periods (6.9% vs 8.8%; odds ratio, 1.06; 95% confidence interval, 0.5-2.2; P = .87).
CONCLUSIONS: Immunizing only postpartum mothers with Tdap vaccine did not reduce pertussis illness in infants ≤6 months of age. Efforts should be directed at immunizing all household and key contacts of newborns with Tdap, not just mothers.