An Article published Online First (www.thelancet.com) and in an upcoming edition of The Lancet shows that pregnant women could be at increased risk for complications from H1N1 flu. Furthermore, the study, from the USA, shows that the rate of hospitalisation for pregnant women is more than four times that of the general population. Pregnant women with H1N1 flu should start antiviral treatment as soon as possible, while those who are well should be vaccinated once a vaccine becomes available. The Article is written by Dr Denise J Jamieson, Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA, USA, and colleagues.
After initial reports of H1N1 infection in pregnant women, the US Centers for Disease Control and Prevention (CDC) began systematically collecting additional information about cases and deaths in pregnant women in the USA as part of enhanced surveillance. A confirmed case was defined as acute respiratory illness with laboratory confirmed H1N1 influenza; a probable case was defined as acute febrile illness with laboratory confirmed influenza A that was negative for seasonal flu types. The rates of admission to hospital and illness were than calculated using data from the 2007 census.
From April 15 to May 18, 2009, 34 confirmed or probable cases of pandemic H1N1 flu in pregnant women were reported to CDC from 13 states; 11 (32%) were admitted to hospital. The estimated rate of admission to hospital for pregnant women (at 0.32 per 100,000 women) was more than four times higher than for the general population (0.076 per 100,000 population at risk). However the authors say that this difference could appear higher because doctors may be more likely to admit a pregnant woman to hospital than someone from the general population with the same symptoms profile. Between April 15 and June 16, 2009, six deaths in pregnant women were reported to the CDC; all were in women who had developed pneumonia and subsequent acute respiratory distress syndrome requiring mechanical ventilation.
The women analysed in the study were of a variety of ages and races. There were five women under 18; 17 aged 18—29; 11 aged 30—39; and one aged over 40. Nine of the women were non-Hispanic white; two non-Hispanic black; 15 Hispanic; 1 Asian; 1 American Indian/Alaskan Native; and six of unknown race. Other characteristics were also mixed: four women had travelled to Mexico in the previous seven days, while 27 had not, and three were unknown. The women were also mixed in their stage of pregnancy: three were 0—13 weeks, 19 were 14—28 weeks, and nine more than 29 weeks pregnant, with three unknown.
The authors say: "Although the decision to admit a pregnant woman is complex and might include considerations beyond simply the severity of disease, that a high proportion (>10%) of influenza-related deaths in the USA have been in pregnant women is concerning. In the previous influenza pandemics of 1918 and 1957, mortality seemed to be higher in pregnant women than in non-pregnant populations... During the pandemic of 1957, 50% of deaths due to Asian influenza in Minnesota among women of reproductive age occurred in pregnant women."
They add: "CDC recommendations for pregnant patients are that antiviral drugs be started as soon as possible after the onset of influenza symptoms. The benefit is expected to be greatest if started within 48 h of onset...However, many pregnant women in our series were not treated with either of these drugs at the time of their presentation with influenza-like illness. Furthermore, none of those who died were treated within 48 h of illness onset."
The authors say that in view of the expected effects of pandemic H1N1 influenza virus on the pregnant woman, the benefits of treatment with anitviral drugs are likely to outweigh potential risks to the fetus, although since most women in this study (and all other pregnant women globally) are still pregnant, little is known about the possible effects of the pandemic H1N1 virus on the fetus.
Regarding vaccination, the authors say: "Once available, vaccination will be an essential component of the public health response to this influenza, and US guidelines place pregnant women in a high-priority group for receipt of pandemic influenza vaccine." However, they add their concerns that few pregnant women currently chose to be immunised against seasonal flu.
The authors conclude: "Findings from this study will be crucial to inform public health planning for pregnant women, both for this virus and for other novel pathogens. Crucially, health-care providers have to realise that pregnant women are at increased risk for severe disease and complications from pandemic H1N1 influenza virus infection, and should start treatment with anti-influenza drugs promptly."
Dr Denise J Jamieson, Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA, USA T) +1 (404) 639-3286 / after hours +1 404 639-2888 E) media@cdc.gov/ DJamieson@cdc.gov
For full Article, see: http://press.thelancet.com/h1n1pregart.pdf
Notes to editors: An accompanying Comment was not ready in time to be included with this Article, however one will be published when the Article appears in a forthcoming issue, details to be announced.
Journal
The Lancet