A recent British study indicates that a particular strain of bacteria is especially dangerous if infection occurs during pregnancy. The Haemophilus influenzae bacterium is associated with increased risk for miscarriage, premature birth, and stillbirth. It is important to note that although its name indicates the flu bug, the flu (influenza) is caused by a virus, not a bacterium, so a flu vaccination will not protect against the H. influenzae bacterium.

The bacterium was first discovered in 1892 amidst an influenza pandemic and was given the name H. influenzae because it was thought to be the cause of the pandemic. In 1933, it was discovered the respiratory illness known as influenza is actually caused by the Orthomyxoviridae virus.

H. influenzae is an opportunistic bacterium that causes localized illness that isn't always associated with respiratory distress. Opportunistic means it resides in the body without causing harm until an opportunity arises when the immune system is challenged. Pregnancy is one such opportunity.

Localized illness means the bacterium affects a specific body part or system, not the full-body illness of the flu. H. influenzae can cause a form of pneumonia but it also causes illnesses such as cellulitis, epiglottitis, infectious arthritis, osteomyelitis, and meningitis. Ear, eye, and sinus infections can occur, too.

The British study, led by Sarah Collins, of London's Public Health England bureau, compared the pregnancy outcomes of 171 women clinically diagnosed with the bacterial infection in England and Wales between 2009 and 2012. The women, aged 15 to 44 years, were under the care of a general practitioner and each completed a questionnaire three months after treatment for infection.

The Collins research team discovered that almost every woman diagnosed with the bacterium developed complications of pregnancy. When infection occurred during the first 24 weeks of pregnancy:

  • 93.6% experienced loss of pregnancy
  • 6.4% experienced extremely premature birth

When infection occurred during the last half of pregnancy:

  • 28.6% experienced premature birth
  • 7.2% experienced stillbirth

The bacterial infection raised the risk for pregnancy loss by 290% over the national average for pregnant women but the overall incidence of bacterial infection is actually very low: just 0.50 per 100,000 women. The study suggests that, although the infection rate during pregnancy is low, the almost-universal consequences are severe and effective treatment is crucial.

The research team writes that H. influenza disease must be taken seriously, even by people not pregnant. The team's recommended treatment includes hospitalization, intravenous antibiotics, and close monitoring that includes follow-up microbiological testing.

Source: Collins, Sarah, et al. “Risk of Invasive Haemophilus influenzae Infection During Pregnancy and Association With Adverse Fetal Outcomes (abstract)." JAMA. The JAMA Network / American Medical Association. Mar 19, 2014. Web. Mar 28, 2014.