Pregnancy may increase risk for H. influenzae infection

In England and Wales, the risk for invasive Haemophilus influenzae appears to be increased in pregnant women, and this risk leads to poor pregnancy outcomes, according to recent findings.

In the prospective national surveillance study, researchers evaluated the association between pregnancy and invasive H. influenzae in 171 women with laboratory-confirmed H. influenzae.

The investigators utilized data on species confirmation and serotyping of all invasive clinical isolates seen at National Health Service (NHS) hospitals, documented by Public Health England. The researchers also requested the completion of a standardized questionnaire by clinicians who treated women aged 15 to 44 years with laboratory-diagnosed invasive H. influenzae between 2009 and 2012. The follow-up incorporated 45,215,800 woman-years.

The study’s primary outcome was H. influenzae infection, and the secondary outcomes pertained to the results of the pregnancies.

Of the 171 women with confirmed H. influenzae infection, 144 (84.2%) had unencapsulated infection, 11 (6.4%) had serotype B and 16 (9.4%) had other encapsulated serotypes. The researchers found that 75 of the 171 women (43.9%; 95% CI, 36.3-51.6) were pregnant at the time of infection. Most of these women were previously healthy.

The prevalence of invasive unencapsulated H. influenzae infection was 17.2 (95% CI, 12.2-24.1) times higher among pregnant women (2.98/100,000 woman-years) compared with nonpregnant women (0.17/100,000 woman-years). There was an association between unencapsulated H. influenzae infection during the first 25 weeks of pregnancy and fetal loss (93.6%; 95% CI, 82.5-98.7), as well as extremely premature birth (6.4%; 95% CI, 1.3-17.5).

When seen during the second half of pregnancy, unencapsulated H. influenzae infection was correlated with premature birth in eight of 28 cases (29%) and stillbirth in two of 28 cases (7%).The incidence rate ratio for loss of pregnancy was 2.91 (95% CI, 2.13-3.88) for all serotypes of H. influenzae and 2.9 (95% CI, 2.11-3.89) for unencapsulated H. influenzae compared with the overall rate for pregnant women.

Morven S. Edwards, MD 

Morven S. Edwards

In an accompanying editorial, Morven S. Edwards, MD, of the department of pediatrics at Baylor College of Medicine, emphasized the importance of enhanced screenings for pregnant women who may be at risk for invasive H. influenzae.

“Infectious diseases are a potentially preventable cause of adverse pregnancy outcomes,” Edwards wrote. “On a broader scale, design of guidelines to ensure that blood cultures and other appropriate samples are obtained in febrile pregnant women, especially during later stages of pregnancy, should be undertaken to clarify the contribution of bacterial infections to fetal loss, stillbirth, and premature delivery.”

For more information:

Collins S. JAMA. 2014;311:1125-1132.

Edwards MS. JAMA.2014;311:1115-1116.

Disclosure: See the full study for a list of relevant financial disclosures.