WEDNESDAY, Oct. 14, 2009 (HealthDay News) -- People who are severely ill with the H1N1 swine flu run the risk of blood clots in the lungs, University of Michigan researchers say.
And because standard chest X-rays may not be able to spot the potentially fatal condition, more sophisticated CT scans may be needed to identify the risk, the researchers said.
Technically called a pulmonary embolism, the condition occurs when one or more arteries in the lungs become blocked. Aggressive use of blood-thinning drugs can reduce the risk of death, the researchers said.
"The high incidence of pulmonary embolism is important. Radiologists have to be aware to look closely for the risks of pulmonary embolism in severely sick patients," study lead author Dr. Prachi P. Agarwal, assistant professor of radiology at the University of Michigan Medical School, said in a university news release.
"With the upcoming annual influenza season in the United States, knowledge of the radiologic features of H1N1 is important, as well as the virus's potential complications. The majority of patients with H1N1 that undergo chest X-rays have normal radiographs. CT scans proved valuable in identifying those patients at risk of developing more serious complications as a possible result of the H1N1 virus," he added.
The Michigan study included 66 patients diagnosed with the H1N1 swine flu; 14 of those were so sick they had to be admitted to the intensive-care unit.
All 66 patients underwent chest X-rays to look for problems caused by the H1N1 virus. Pulmonary embolisms were detected by CT scans in five of the 14 intensive-care unit patients. The researchers added that initial chest X-rays were normal in more than half of the patients with H1N1 infections.
"These findings indicate that imaging studies would have to be repeated in severely ill patients to monitor disease progression," said study co-author Dr. Ella Kazerooni, director of the University of Michigan's division of cardiothoracic radiology. "It's important to heighten awareness not only among the radiologists, but also among the referring clinicians."
The study findings are to be published in the December issue of the American Journal of Roentgenology.
Also Wednesday, the vaccine maker Sanofi Pasteur said tests are showing that children under 10 years of age may need two doses of the H1N1 swine flu vaccine to be fully protected, the Associated Press reported.
U.S. health officials said the finding isn't surprising because children in this age group typically need two doses of regular seasonal flu vaccine because their immune systems aren't fully developed.
Sanofi is the only company licensed in the United States to make vaccine for children as young as 6 months old. The company tested two strengths of the H1N1 vaccine, given as two shots 21 days apart. The vaccine was tested in 474 children ages 6 months through 9 years old. With one shot, only half of children 6 months to 3 years old had enough immunity, as did three-fourths of children 3 to 9 years old, Sanofi said, the AP reported.
Clinical trials involving adults have shown that one shot is sufficient.
On Tuesday, a leading disease-surveillance expert from Europe reported that the swine flu is killing fewer people than seasonal flu, but is causing greater alarm because it's targeting an unusually large number of children, who typically are less susceptible to flu than older adults.
Denis Coulombier, head of the European Centre for Disease Prevention and Control's preparedness and response unit, told the Agence France-Presse news service that the H1N1 swine flu has killed a very small proportion of those infected with the virus -- about 0.2 to 0.3 deaths per 1,000. That compares to a fatality rate from seasonal flu of roughly one patient per 1,000, he said.
Also on Tuesday, a U.S. health official said that, while the majority of people hospitalized with the H1N1 swine flu have chronic medical conditions, many were healthy before coming down with the disease.
More than half of hospitalized adults had conditions such as asthma, chronic lung diseases, heart disease or immune system disorders, Dr. Anne Schuchat, director of the U.S. Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, said during a press conference.
But, she added, "This virus can be serious even in people with no underlying conditions."
Among adults hospitalized with the H1N1 swine flu, 45 percent did not have a pre-existing medical problem and 6 percent were pregnant, Schuchat said. Among hospitalized children, 5.8 percent had sickle anemia or another blood disorder, she said.
"The most common underlying conditions [for children] were asthma and chronic lung disease, neuromuscular diseases and sickle cell or other blood disorders," Schuchat said.
The findings were based on data collected on 1,400 hospitalized adults and more than 500 hospitalized children whose medical centers participate in the CDC's Emerging Infections Program Network, she said.
As of last Friday, 12,384 people in the United States had been hospitalized with influenza since August, and 1,544 had died, including 81 children, according to the CDC.
The number of pediatric deaths from the H1N1 swine flu is higher than usually seen with regular seasonal flu. During the past three years, deaths among children from the regular seasonal flu ranged from 46 to 88 annually, Schuchat said last Friday.
About 30 percent of the children who died had chronic medical conditions, such as asthma, cerebral palsy and muscular dystrophy. Among adults, about 30 percent died of severe bacterial pneumonia, she said Friday.
Schuchat said Tuesday that 9.8 million doses of the H1N1 vaccine are available. "I am happy to say that about half of the vaccine that's available for order is now the injectable form," she said.
The first batches of the vaccine were in a nasal spray called FluMist. Because FluMist is a live vaccine, it's only recommended for healthy people between 2 and 49 years old, and not for pregnant women, Schuchat said.
Schuchat said the availability of the H1N1 vaccine will continue to grow, and ample supplies should be on hand by the end of October and early November. The CDC has been saying for some time that it anticipates having 40 million doses by the end of October and 190 million doses by year's end.
"Pregnancy and underlying conditions are ones that we highlight as recommended to receive the H1N1 vaccine when it becomes available in communities," she said.
As for the regular seasonal flu, Schuchat said 77 million doses of that vaccine have been shipped. Although some parts of the country are seeing shortages of the vaccine, those shortfalls are expected to be temporary, with large quantities of the vaccine to be available in late October and November.
Since the seasonal flu season hasn't started yet, there's plenty of time to get a seasonal flu shot, even into December, Schuchat said.
More information
For more on the H1N1 flu, visit the U.S. Centers for Disease Control and Prevention.
