Infants <4 months of age are at greatest risk of severe disease and death from pertussis. For over a decade, Hispanic infants have had higher incidence of pertussis; reasons for this are unclear, however larger households observed among many Hispanic families may lead to greater opportunities for exposure. All women are recommended to receive Tdap vaccine at 27-36 weeks gestation of each pregnancy to protect infants in the early weeks of life, however uptake of this vaccine has been suboptimal.
METHODS:
We evaluate the 2013 California birth cohort and compare maternal demographics between infants who became infected with pertussis at <4 months of age and uninfected infants to determine characteristics associated with increased risk within different racial/ethnic groups.
RESULTS:
239 infants born in 2013 were reported with pertussis at <4 months of age and linked with their birth certificate records. Mothers of infected infants were significantly more likely to be Hispanic (OR 1.9, 95% CI 1.5-2.5) and significantly less likely to be Asian/Pacific Islander (API) (OR 0.4, 95% CI 0.3-0.7) or white (OR 0.7, 95% CI 0.5-0.5) [no difference observed for black]. API and black mothers of infected infants were less likely to be foreign-born with no difference observed in other racial/ethnic groups.
When controlling for race/ethnicity, infants infected with pertussis were significantly more likely to have older siblings (OR 1.2 for each additional sibling, 95% CI 1.1-1.4) and to be covered by Medicaid insurance (OR 1.5, 95% CI 1.2-1.7). There were no differences observed between infected and uninfected infants in maternal age, the number of prenatal visits received, infant’s birth weight or gestational age.
Regional differences were observed and more cases than expected were reported from Southern California, the Northern Coast and the Central Valley.
CONCLUSIONS:
Infants <4 months of age of all racial/ethnic groups who have older siblings are at increased risk of pertussis, consistent with a recent study indicating that siblings are now the most common source of B. pertussis for young infants. Hispanic infants and infants with Medicaid insurance are also at increased risk of pertussis. Efforts should be made to encourage prenatal care providers to strongly recommend that their patients receive Tdap vaccination during the 3rd trimester of each pregnancy, regardless of their prior Tdap vaccination history. To minimize barriers, Tdap vaccine should be offered during routine prenatal visits. Siblings and other household members of young infants should also be up-to-date on pertussis vaccinations.