Severe Swine Flu Could Lead to Blood Clots in Lungs: Study

Researchers say CT scans may be needed to spot the risk

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By Steven Reinberg
HealthDay Reporter

WEDNESDAY, Oct. 14 (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.