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Beware of invasive H influenzae disease among pregnant women

Pregnant women are about 17 times as likely as nonpregnant women to contract invasive unencapsulated Haemophilus influenzae disease, and when they do, it almost always heralds poor pregnancy results, a new study reports1


Experts generally have not considered H influenzae disease to be a substantial contributor to severely adverse fetal outcomes. Yet new research from England and Wales finds that even though pregnant women in their study tended to be younger and healthier than their nonpregnant counterparts, they were far more likely to develop the invasive unencapsulated form of disease and far more likely to present with bacteremia. Not to mention that almost all of their pregnancies resulted in miscarriage, stillbirth, extremely preterm birth, or, at best, the birth of infants with respiratory distress with or without sepsis.


Collins and colleagues queried prospectively general practitioners who cared for women of reproductive age (15 to 44 years) with invasive H influenzae disease during the 4-year period of 2009 to 2012. One hundred percent of those queried responded. The study encompassed more than 45 million woman-years of follow-up.

Of the 171 women who developed the infection (confirmed by positive culture from a normally sterile site), approximately 84% (144) had unencapsulated disease. Not quite half (44% or 75) of the 171 women were pregnant at the time of infection. The overall incidence of confirmed invasive H influenzae disease was low at 0.50 per 100,000 women of reproductive age, but the 75 pregnant women were 17.2 (95% confidence interval [CI], 12.2-24.1; P<.001) times as likely to develop the infection as the 96 nonpregnant women (2.98/100,000 woman-years versus 0.17/100,000 woman-years, respectively). And, despite being previously healthy, almost three times as many pregnant as nonpregnant women presented with bacteremia (90.3% versus 33.3%, respectively).

Of 47 women who developed unencapsulated H influenzae infection during the first 24 weeks of pregnancy, 44 lost the fetus and three had extremely preterm births. Of 28 women who developed the infection during the second half of their pregnancy, two had stillbirths. Eight of the 26 live births were preterm, and 21 of the 26 infants had respiratory distress with or without sepsis at birth. The researchers calculated that the rate of pregnancy loss following invasive H influenzae disease was almost 3 times higher than the average rate of pregnancy loss in England and Wales.


It is generally reported that up to one-quarter of the approximately 26,000 stillbirths occurring yearly in the United States are due to some type of maternal or fetal infection.2,3 Dr. Morven S. Edwards, in an editorial4 appearing in the same issue of JAMA as the study, comments, “Given the magnitude of the burden of perinatal deaths, clarifying the extent that bacterial infections result in stillbirth and preterm delivery could potentially inform interventions to improve child and maternal health globally.”

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