Understanding Influenza Hospitalization Among Pregnant Women

Despite increased risk of seasonal influenza-related hospitalizations, data about the epidemiology of severe influenza among pregnant women has primarily been focused on exceptional pandemic events. This lack of data limits assessments of the overall health burden of seasonal influenza among women who are pregnant.

A new study published in The Journal of Infectious Diseases offers insight on cases of seasonal influenza hospitalization among pregnant women, using administrative and health record data to characterize such cases in ways which may aid future public health efforts.

Data were collected across 6 influenza seasons from 2010 to 2016 in Canada, Israel, and the United States. In Australia, data covered 4 influenza seasons from 2012-15. The study sites used local data to identify a retrospective cohort of all women between 18 and 50 years of age with pregnancies that overlapped with a local influenza season.

Investigators sought hospitalizations with a country-relevant discharge diagnosis code for acute respiratory infection or febrile illness (ARFI) and influenza-associated ARFI. Hospitalizations were included in the main analysis if they included clinical testing of >1 respiratory specimen for influenza viruses within 3 days of hospital admission.

Illness outcomes, pregnancy outcomes, and socioeconomic status were assessed.

Out of a total of 18,048 hospitalizations with ARFI codes, 1064 included testing for influenza viruses. Of the cases tested 614 (58%) were positive.

The median length of influenza hospitalizations for this group was 2 days (interquartile range: [IQR] 1-4). Delivery occurred during hospitalization in 18% of women (95% confidence interval: [CI] 15-21%). Among hospitalizations that resulted in a delivery, median hospital stay rose to 3 days (IQR: 2-6).

Out of the 110 influenza associated hospitalizations that resulted in delivery during the patient’s stay, 101 had available outcome data. Of the 101 deliveries with available outcome data, 94-100% were live births.

Notably, 25-34% of influenza-positive hospitalizations that resulted in deliveries were preterm. This is substantially higher than the estimated baseline preterm birth prevalence of 9% among women in high-income countries.

Pneumonia was diagnosed in 10% of hospitalizations, 5% (95% CI: 3-6%) necessitated intensive care, 2% (95%: CI 1-3%) resulted in a sepsis diagnosis, and <1% (95% CI: 0-1%) resulted in respiratory failure. There were no maternal deaths reported.

Out of the 614 influenza-positive hospitalizations, 35% were women with socioeconomic disadvantage. In addition, 80% were previously healthy without underlying conditions and 67% were in the third trimester of pregnancy.

A majority of hospitalizations and influenza positive hospitalizations occurred in women who did not receive a seasonal influenza vaccine.

“These data suggest that while clinical outcomes of pregnant women hospitalized with seasonal influenza may be less severe than for some other high-risk groups, the burden of critical illness in pregnant women is not trivial,” study authors wrote.