Following Birth Hospitalization: Invasive Bacterial Infections in Preterm Infants Aged 7-90 Days

To assess the incidence rate of invasive bacterial infections in preterm infants and compare invasive bacterial infection rates and pathogens between preterm and full-term infants at age 7-90 days.

This is a retrospective cohort study of the incidence rate of invasive bacterial infections among all infants born at Kaiser Permanente Northern California (KPNC), with blood and cerebrospinal fluid cultures collected between 7 and 90 days of chronological age from outpatient clinics, from emergency departments, and in the first 24 hours of hospitalization presenting for care between January 1, 2005, and December 31, 2017. Incidence rates of invasive bacterial infection by chronological age and postmenstrual age (PMA) and pathogens were compared between preterm and full-term infants.

Between January 1, 2005, and December 31, 2017, a total of 479 729 infants were born at KPNC, including 440 070 full-term infants and 39 659 preterm infants. There were 283 cases of bacteremia in 282 infants. The incidence rate of invasive bacterial infection was significantly higher for preterm infants compared with full-term infants. The highest incidence rates of invasive bacterial infection were in preterm infants at chronological age 7-28 days and/or 37-39 weeks PMA. There was a trend toward lower rates of invasive bacterial infection with increasing PMA in preterm infants aged 61-90 days. Preterm infants aged 29-60 days or at ≥40 weeks PMA and those aged 61-90 days or at ≥43 weeks PMA had a rate of invasive bacterial infection equivalent to the overall rate seen in full-term infants of the same chronological age group. The distribution of pathogens causing bacteremia and meningitis did not differ between preterm and full-term infants.

PMA and chronological age together were more useful than either alone in informing the incidence rate of invasive bacterial infection in preterm infants during the first 90 days of life.