Optimizing recovery of Haemophilus influenzae from vaginal-rectal specimens and determining carriage rates in pregnant women.

Purpose: Haemophilus influenzae (HINF), primarily non-typeable H. influenzae: (NTHi), is an important cause of neonatal sepsis and meningitis. The goal of this study was to investigate the point prevalence of HINF vaginal-rectal carriage in pregnant women, which could impact neonatal health.

Methods: Simulated vaginal-rectal swabs were cultured and tested to establish optimal recovery methods for HINF. These methods were then applied to vaginal-rectal swabs from a prospective cohort of pregnant women (n = 300) undergoing routine Group B Streptococcus: (GBS) screening. Both culture and PCR were used for detection of HINF. Subject demographics, reproductive history, and genitourinary test results were documented. A retrospective surveillance study was conducted to determine incidence of invasive neonatal HINF infections from 7/1/2017-6/30/2023.

Results: HINF was recovered from 42/42 (100%) simulated vaginal-rectal swabs at 2-45 CFU/plate via direct plating onto chocolate and chocolate + bacitracin agar. HINF was rarely recovered following LIM broth enrichment at 0-75 CFU/plate in 1/42 (2.4%) simulated swabs, but was recovered from BHI/Fildes broth enrichment in 22/42 (52%) specimens at high abundance (> 100 CFU/plate). Among pregnant women prospectively screened for HINF, the median age was 29 (IQR, 24-33) years and gestational age was 36 (IQR, 34-36) weeks. HINF was recovered in 1 of 300 prospective specimens by culture but 0/100 by PCR. A six-year retrospective analysis showed there were seven total cases of neonatal sepsis and majority of HINF was isolated from respiratory specimens followed by blood/CSF overall.

Conclusion: This study established a sensitive culture method for recovering HINF from vaginal-rectal swab specimens and demonstrated low prevalence of HINF carriage rate in pregnant women. These findings highlight the need for further research to pinpoint the source for transmission of HINF to neonates.