Pregnancy Increases Risk of Severe H1N1 Disease

Pregnant women are at greater risk for severe disease and complications from H1N1 pandemic flu than the general public, researchers said. Pregnant women should be treated promptly with antiviral drugs if the pandemic flu strain is suspected, according to Denise Jamieson, MD, of the CDC, and colleagues. The recommendation is based on an analysis of cases and deaths of pregnant women from the pandemic strain in the early weeks of the U.S. outbreak, Dr. Jamieson and colleagues reported online in The Lancet.

The findings underscore the CDC recommendation that pregnant women with the flu should receive prompt antiviral treatment and may also have implications for the use of a vaccine against the pandemic. “If a pregnant woman feels like she may have influenza, she needs to call her healthcare provider right away,” Dr. Jamieson said in a statement.

In addition, she said, doctors treating/caring for pregnant women need a triage system to screen for influenza-like symptoms “and they should not delay in initiating appropriate antiviral therapy.” Dr. Jamieson said some doctors hesitate to use antiviral drugs in pregnant women “because of concerns for the developing fetus, but this is not the correct approach in this instance. It is critical that pregnant women, in particular, be treated promptly.”

During the first month of the outbreak of the H1Nl virus, from April 15 to May 18, 34 (thirty four) confirmed or probable cases of pandemic H1N1 in pregnant women were reported to the CDC from 13 states, the researchers found. Confirmed cases were those with laboratory evidence of H1N1; probable cases were those in which the victim had an acute febrile respiratory illness and was positive for influenza A, but negative for H1 and H3, Dr. Jamieson and colleagues said. Of the 34 cases, 11 (eleven) — or 32% — required inpatient care, for an estimated hospital admission rate of 0.32 per 100,000 pregnant women, compared with 0.076 per 100,000 in the general population at risk, they said. By June 16, 6 (six) H1N1-related deaths in pregnant women had been reported to the CDC, all in women who had developed pneumonia and subsequent acute respiratory distress syndrome requiring mechanical ventilation (a tube inserted to help the patient breathe.) That was 13% of the 45 deaths reported during that period, the researchers said. Of the six who died, one was in the first trimester, one in the second trimester, and four were in the third trimester ; all were “fairly healthy” pregnant women before their illness, the researchers said. All the women were treated with oseltamivir (Tamiflu) and the time from symptom onset to treatment ranged from six to 15 days, they said.

The five patients with viable pregnancies had cesarean sections and none of the infants were born with flu. Four have been discharged home in good health, while the fifth — born at 27 weeks gestation — remains in the hospital and is doing well, Dr. Jamieson and colleagues said.

Meanwhile, the issue seems likely to kindle debate over who should get the H1N1 vaccine when it becomes available. “There are two broad goals in using a vaccine,” said Marc Lipsitch, DPhil, of Harvard University, “to protect people who are likely to get severely ill if they are infected, and to slow down transmission by vaccinating the people who are most likely to get infected and pass the virus on.” But the second goal is going to be difficult to reach since current estimates show the vaccine arriving on the scene well after the second wave of the pandemic starts this fall, he said. “Therefore,” Dr. Lipsitch said, “it is very wise to plan to use vaccines mainly to protect those most vulnerable.” But he cautioned that it will be vital to monitor vaccine safety, since pregnant women, and some other potentially high-risk groups, are also at higher risk for other adverse events. “This means that even with a perfectly safe vaccine, there will be (by chance) people who receive the vaccine and then very shortly after experience adverse health events,” he said. To avoid a possible backlash, Dr. Lipsitch said, “it is critical for the public and the health community to understand in advance that adverse events in vaccinated people are expected to happen, and their occurrence is not in itself an indication that the vaccine is unsafe.”

Carlos del Rio, MD, of Emory University in Atlanta, concurred that safety is an important issue. “The vaccine (as far as I can tell) has not yet been tested for safety in pregnancy,” he said. Dr. del Rio said it’s not surprising that pregnancy appears to be a risk factor for severe H1N1 disease. “Pregnancy is also a risk factor for other infectious diseases to be more severe,” he said. “Thus, it makes sense that (pregnant women) should be immunized.”

On the other hand, he said, obesity also appears to be a risk factor for more severe disease, so this group might also be considered as a priority group. The principle that should guide vaccine use is that “limited vaccine needs to go where it will do most good and prevent the most serious cases or deaths,” according to Howard Markel, MD, PhD, of the University of Michigan in Ann Arbor. Pregnant women, the obese, and those with asthma and diabetes appear to be such groups, he said, “but we also need to think of first responders,” including doctors, nurses, police, and fire personnel. “Even the people who keep our power lines, coal, water, electricity, and energy lines going — we don’t want any of these people out in time of a national crisis,” Dr. Markel said.

The CDC’s former director, Julie Gerberding, MD, said vaccinating pregnant women would have a double benefit. It “protects mom and also likely protects newborns until they are old enough to be vaccinated or take antivirals, she said.

The authors noted several limitations of the study including the fact that “ascertainment of women infected with pandemic H1N1 influenza virus was dependent on surveillance and laboratory testing methods used by state public health authorities during the outbreak. These methods varied by state and by the timing during the outbreak.” Other limitations include the fact that that pregnant women might be less likely to be tested than were those who were not pregnant and that “healthcare providers might be more likely to admit a pregnant woman than a nonpregnant person with similar findings, which could lead to an exaggerated admission rate in pregnant women.”

The study was supported by the CDC. Dr. Jamieson and several other authors are employees of the agency. No other potential conflicts were reported.

By Michael Smith, North American Correspondent, MedPage Today
Published: July 29, 2009
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine and
Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

Primary source: The Lancet
Source reference:
Jamieson DJ, et al “H1N1 2009 influenza virus infection during pregnancy in the USA” Lancet 2009; DOI: 10.1016/S0140-6736(09)61304-0.