New Data Underscore the Dangers of H influenzae Infection in Pregnancy

March 31, 2014

Miscarriage and stillbirth can occur in pregnant women with Haemophilus influenzae infection. Here, new data quantify the risk and reveal which bacteria type poses the most threat.

Pregnant women are at greater risk for respiratory infection with Haemophilus influenzae, according to a surveillance study published in a recent issue of JAMA.

The study, which used national health surveillance data gathered by Public Health England and included women in England and Wales, also showed that the bacterial infection was associated with miscarriage and stillbirth. 

Pertinent Points

- Pregnant women
are at greater risk for respiratory infection with invasive Haemophilus influenzae, according to a 4-year surveillance of public UK data.

- The unencapsulated strain of the disease was significantly more likely to cause miscarriage or stillbirth in pregnant women.

The data revealed that 171 women had laboratory-confirmed invasive H influenzae infection, which included 144 (84.2%) with unencapsulated type (95% CI, 77.9%-89.3%), 11 (6.4%) with serotype b (95% CI, 3.3%-11.2%), and 16 (9.4%) with other encapsulated serotypes (95% CI, 5.4%-14.7%), according to the results. And overall, 75 (43.9%) of the 171 women were pregnant at the time of infection, with most of the pregnant women previously reported to be healthy.

For the surveillance, general practitioners caring for women ages 15 to 44 years with laboratory-confirmed invasive H influenzae infection during 2009 to 2012 were asked to complete a clinical questionnaire three months after infection. All questionnaires were completed.

Pregnant women appeared to be at higher risk mainly because of the unencapsulated strain of the disease. According to the CDC, unencapsulated strains generally are associated with noninvasive infections but can cause invasive disease in persons with weakened immune systems, such as pregnant women and neonates. The incidence rate of invasive unencapsulated H influenzae disease was 17.2 times greater among pregnant women compared with nonpregnant women (2.98/100,000 vs 0.17/100,000 woman-years, respectively; 95% CI, 12.2-24.1; P<0.001).

Of the 47 pregnant women with unencapsulated H influenzae infections occurring during the first 24 weeks of gestation, 44 (93.6%) miscarried (95% CI, 82.5%-98.7%). During the second half of pregnancy, unencapsulated H influenzae infection was associated with premature birth in 8 (28.65) of 28 cases (95% CI, 13.2%-48.7%) and stillbirth in 2 (7.1%) of 28 cases (95% CI, 0.9%-23.5%).

Overall, the results showed that pregnancy loss following invasive H influenzae disease was 2.9 times higher than the UK national average.