Surveillance of A/H1N1v influenza in pregnancy

Summary

This research identified through UKOSS, all pregnant women hospitalised with confirmed influenza A/H1N1v in the UK between September 2009 and January 2010.

Key findings

• Women hospitalised with AH1N1v in pregnancy in the UK during the 2009 pandemic were significantly at risk of maternal and pregnancy complications: 1.7% of women admitted to hospital with confirmed AH1N1v influenza in pregnancy died (95% CI 0.5-4.2%), an estimated 1.6 deaths per 100,000 maternities (95% CI 0.5-3.7).
• Eighty-three percent of women hospitalised with A/H1N1v influenza were treated with antiviral agents, but only 6% received antiviral treatment before hospital admission.Treatment within two days of symptom onset was associated with an 84% reduction in the odds of admission to an intensive care unit (ICU) (OR 0.16, 95%CI 0.08-0.34); in the context of high circulating levels of influenza in the community, early use of antiviral agents (oseltamivir or zanamivir) in pregnant women with influenza symptoms is important.
• Maternal obesity during pregnancy is associated with both admission to hospital with confirmed infection and critical illness from AH1N1v. This highlights the importance of ongoing work to support obesity prevention at a community level.
• Maternal smoking, particularly in younger mothers, is also associated with admission with AH1N1v in pregnancy. Smoking in pregnancy is associated with a number of risks to both mother and fetus and thus prevention programmes continue to be important.
• There was a significantly higher ICU admission risk in Australia and New Zealand than in the UK in 2009 (risk ratio 2.59, 95% CI 1.75–3.85), which may reflect the success of clinical and public health interventions in the UK in the second phase of the pandemic
• The first analyses into the effects of 2009/H1N1 influenza “swine flu” in pregnancy focused primarily on maternal morbidity and mortality.Few studies followed-up women after their original hospital admission, thus the effect of infection on pregnancy outcome was not fully investigated.Pregnancy outcome data were obtained for 94% of women (n=256).

• The perinatal mortality was higher amongst infants born to infected women (39 per 1,000 total births, 95%CI 19 to 71) compared to infants of uninfected women (7 per 1,000 total births, 95%CI 3 to 13) (p<0.001). This was principally explained by an increase in the stillbirth rate (27 per 1,000 total births vs 6 per 1,000 total births; p=0.001). Infants of infected women were also more likely to be born prematurely (aOR 4.0, 95%CI 2.7 to 5.9).
• This study emphasises the importance of immunisation against influenza for all pregnant women to prevent both poor maternal and perinatal outcomes.

Publications

Journal Articles

• Yates L, Pierce M, Stephens S, Mill A, Spark P, Kurinczuk JJ, Brocklehurst P, Thomas S, Knight M. Influenza A/H1N1v in pregnancy: an investigation of the characteristics and management of affected women and the relationship to pregnancy outcomes for mother and infant. Health Technol Assess. 2010;14(34):109?82
• Knight M, Pierce M, Seppelt I, Kurinczuk JJ, Spark P, Brocklehurst P, McLintock C, Sullivan E, on behalf of the Uk?s Obstetric Surveillance System, the ANZIC Influenza Investigators, and the Australasian Maternity Outcomes Surveillance System. Critical illness with AH1N1v influenza in pregnancy: a comparison of two population-based cohorts. Br J Obstet Gynaecol. 2011;118(2):232-9.
• Pierce M, Kurinczuk JJ, Spark P, Brocklehurst P, Knight M. Perinatal outcomes after maternal 2009/H1N1 infection: national cohort study. Br Med J. 2011;342:d3214.
• Knight M, Lim B. Immunisation against influenza during pregnancy. Br Med J. 2012;344:e3091.