HealthDay News — The incidence of Haemophilus influenzae disease is becoming more common among pregnant women, and infection correlates with poor pregnancy outcomes, according to a study published in the Journal of the American Medical Association.

Sarah Collins, MPH, from Public Health England in London, and colleagues surveyed general practitioners to describe the epidemiology, clinical characteristics and outcomes of invasive H. influenza disease in women of reproductive age (15 to 44 years) from England and Wales.

The researchers identified laboratory-confirmed invasive H. influenzae infection in 171 women, which included 144 with unencapsulated, 11 with serotype b, and 16 with other encapsulated serotypes. At the time of infection, 43.9% of women were pregnant, most of whom were previously healthy.

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Although the overall incidence of H. Influenzae was low, disease expression was different between pregnant and nonpregnant women. Most pregnant women presented with unencapsulated H. influenzae bacteremia, with the invasive unencapsulated H. infuenzae disease incidence rate 17.2-fold higher for pregnant versus nonpregnant women.

Even though pregnant women were younger and healthier, they were more likely to present with bacteremia or pneumonia than nonpregnant women (90.3% vs. 33.3%).

Unencapsulated H. influenzae infection during the first 24 weeks of pregnancy correlated with fetal loss and extremely premature birth, while infection during the second half of pregnancy correlated with premature birth and stillbirth.

For all serotypes of H. influenzae and for unencapsulated H. influenzae, the incidence rate ratio for pregnancy loss was 2.91 and 2.90, respectively, compared with the background rate for pregnant women. “These infections were associated with poor pregnancy outcomes,” the researchers wrote.

Among the 47 women who had an unencapsulated H. influenzae infection in the first 24 weeks of gestation, 44 miscarried, and among the two women who acquired infections after 24 weeks gestation, both had stillborn infants.

In an accompanying editorial, Morven S. Edwards, MD, of Baylor College of Medicine in Houston, Texas, called the study findings “provocative,” noting that, “H. influenza has not previously been considered a substantial contributor to fetal death or stillbirth.”


  1. Collins S et al. JAMA. 2014;311(11):1125-1132.
  2. Morven MS. JAMA. 2014; 311(11):1115-1116.

Disclosures: Several authors disclosed financial ties to the pharmaceutical industry.