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    Studies Confirm Likely Cause of SARS

    New Coronavirus Never Before Seen in Humans

    SARS still spreading, but no U.S. deaths continued...

    Second, it is also possible this country hasn't seen a so-called "super-spreader" of SARS. Evidence from the disease outbreaks in Hong Kong and Canada suggests that some people are particularly effective at transmitting the disease for unknown reasons.

    Finally, the CDC is using a different and broader definition of SARS cases that it reports to the WHO compared with other countries. The agency reports "suspected" SARS cases that meet criteria according to symptoms and travel history and are currently under investigation rather than the "probable" case definition used by other countries.

    Gerberding says the hope is that the CDC is over-diagnosing SARS to cast the broadest possible net and prevent further transmission of the disease. Once reliable diagnostic tests become widely available, she says it is likely that many of these suspected cases will be ruled out.

    Three diagnostic tests are currently in use at the CDC, but researchers must show that they produce consistent results before they can become available for widespread use.

    Gerberding also addressed recent reports that SARS might potentially pose a threat to the international blood supply.

    "We have absolutely no evidence that blood has been a source of transmission of SARS," says Gerberding.

    But as an additional precaution, the CDC is working with the Red Cross and FDA to develop a way to screen and defer blood donations from recent travelers from affected areas who may be infected with SARS but not yet developed symptoms.

    Isolating the Cause of SARS

    Two studies released today in TheNew England Journal of Medicine and another released this week by the British medical journal The Lancet describe the efforts researchers at the CDC and other international laboratories took in isolating a coronavirus as the likely cause of SARS.

    Investigators say the identification was the result of a combination of classical and modern techniques including tissue-culture isolation to amplify the agent, electron-microscopy to identify the virus, and molecular studies to confirm the identity of the virus and link it to SARS.

    These tests showed the virus was not one of the two coronaviruses known to infect humans or those known to cause disease in animals.

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