October 13, 2009 — More than half of 1400 adults hospitalized with influenza A (H1N1) have had underlying medical conditions, including asthma and other chronic lung diseases, chronic heart disease, and immunosuppressive disorders, an official from the US Centers for Disease Control and Prevention (CDC) said today.
In addition, of more than 500 patients younger than 18 years hospitalized with H1N1 infection, most already had another illness such as asthma, lung disease, neurologic and neuromuscular disorders, and sickle cell disease and other blood disorders, said Anne Schuchat, MD, director of the National Center for Immunization and Respiratory Diseases at the CDC, during a press conference.
The data reflect cases reported from April through August to the agency's Emerging Infections Program network in a group of 10 states and expand on an initial CDC study of 272 patients hospitalized with the virus. Dr. Schuchat said the findings from the larger patient sample mirror those from the first batch.
Of the hospitalized adult patients, 26% had asthma, 10% had diabetes, 8% had other lung diseases, and 7.6% had immunosuppressive disorders. Another 6.1% were pregnant women. (No percentage was cited for chronic heart disease.) Dr. Schuchat noted that the underlying illnesses reported were those that the CDC had identified as risk factors that justified vaccinating such patients before others.
More than 45% of adults hospitalized with the virus had no underlying condition that the CDC considers a risk factor, said Dr. Schuchat, adding that this figure did not take into account whether these patients were obese or not. According to the CDC, obesity has emerged as an underlying medical condition in some hospitalized H1N1 patients, although its importance as a contributing factor to complications is unknown.
Immune System Changes Help Put Pregnant Women at Risk
Dr. Schuchat said the preliminary analysis of the 1400 adults and 500-plus children hospitalized with H1N1 influenza infection did not contain a breakdown by sex. These data take on greater significance in light of a study reported by Medscape Infectious Diseases and published October 12 in the Journal of the American Medical Association of 168 critically ill Canadians who were hospitalized with confirmed or probable cases of H1N1 infection. Of these patients, 67.3% were women.
Dr. Schuchat explained why the H1N1 virus is taking a disproportionately heavy toll on pregnant women: A woman's immune system changes during pregnancy to prevent an immune reaction against the fetus, she explained. "The risk of infections can be greater.
"The other reason is mechanical. As the womb gets larger, with the baby growing, there can be pressing on the airways and a restrictive lung disease. So it's harder to take a deep breath, and it's harder to fight off a lung infection, especially in the later stages of pregnancy," Dr. Schuchat said.
Half of Available H1N1 Vaccine Doses Now Are Injectable Variety
While stressing the importance of vaccinations for pregnant women, Dr. Schuchat noted that the first H1N1 vaccines to reach the public were the intranasal version with live but weak viral material that is not recommended for these women. The CDC recommends that pregnant women receive the injectable form of the vaccine with the inactivated virus.
As of yesterday, Dr. Schuchat said, vaccine manufacturers had 9.8 million doses of H1N1 vaccine available for state and local public health agencies to order, with these agencies having requested 5.8 million doses. Of the 9.8 million doses, half were injectable. Dr. Schuchat said these injectable doses should start reaching vaccine dispensers later this week, although they will not be available on a widespread basis until the end of October.
Meanwhile, some 77 million doses of seasonal influenza vaccine have been distributed, she said. Acknowledging regional shortages, she said more doses would reach the public in November and noted that most influenza cases now involve the H1N1 strain as opposed to the seasonal strain.
"The main message I have is to be patient," said Dr. Schuchat. "We think there's time to be vaccinated against seasonal flu, even if vaccine isn't available until November or December. We think it will be just fine to be vaccinated then."
Dr. Schuchat also reported that the CDC had received reports of 5 more children dying from H1N1 influenza, bringing the total since April to 81.