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Background: Pertussis morbidity is increasing, especially among young infants and children, who are more likely to be hospitalized and have more severe complications. Maternal and pediatric factors associated with underimmunization and hospitalization for pertussis are poorly understood, but young maternal age and low birth weight have been associated with pertussis among young infants.

Methods: We used pertussis surveillance data, matching cases to the birth certificates of 416 Texas infants and children reported as pertussis cases during 1995 to 2000. Maternal/pediatric information gathered from birth certificates included birth weight, gestational age, and maternal factors (age, birthplace and education level, prenatal care, and previous live births). We assessed the immunization status of the cases and maternal/pediatric factors associated with underimmunization with a pertussis-containing vaccine and hospitalization using descriptive statistics and logistic regression.

Results: The 416 cases represented 20% of the pertussis morbidity in Texas from 1995 through 2000. Most children had not been vaccinated (275 [66%]), even though 374 (90%) were old enough for at least one dose. Among those 374 children, only those younger than 6 months were associated with underimmunization (odds ratio [OR], 9.98; 95% confidence interval [CI], 6.24-15.97). Most patients (253 [61%]) were hospitalized. Hospitalization was associated with complications of apnea (OR, 2.13; 95% CI, 1.39-2.38), pneumonia (OR, 5.26; 95% CI, 2.94-11.59), and age younger than 6 months (OR, 2.11; 95% CI, 1.38-3.23).

Conclusion: More than two-thirds of the children reported as pertussis cases were old enough to have at least one dose of a pertussis-containing vaccine but were not immunized. Maternal and pediatric characteristics on birth certificates were not useful in predicting either underimmunization or hospitalization for pertussis complications. More current assessments of maternal and pediatric characteristics should be part of pertussis contact investigations.

(C) 2003 Southern Medical Association