http://www.nytimes.com/2003/04/25/science/sciencespecial/25INFE.html?pagewan ted=print&position=
April 25, 2003 Canadian Strain of Virus Appears to Be Stronger Than U.S. Variety By LAWRENCE K. ALTMAN leading American virologist who has just returned from advising Hong Kong officials on the SARS epidemic there said yesterday that death rates from the illness may vary among countries, in part because of differences in strains of the virus. The virologist, Dr. Robert Webster of St. Jude Children's Research Hospital in Memphis, said that one reason the United States has escaped Canada's difficulties with the disease, severe acute respiratory syndrome, is that "the virus they have got in Canada appears to be a more virulent strain than the one seen so far in the United States." Dr. Webster also said that an outbreak of SARS in an apartment complex in Hong Kong seemed to be caused by a different strain from the one causing illness elsewhere in Hong Kong. Speaking at a news conference the morning after his return, Dr. Webster said he and his colleagues in Hong Kong think there are likely to be many strains of the SARS virus. The World Health Organization says the virus, a previously unknown member of the coronavirus family, is the cause of SARS. How big a global problem the disease becomes will "depend on the evolution of this virus, and whether the more pathogenic strains" that spread well become established, Dr. Webster said. But Dr. Webster, who is a world expert on the influenza virus, did not provide specific information about laboratory studies that have identified different strains of the SARS virus. At another news conference later in the day, Dr. Julie L. Gerberding, the director of the Centers for Disease Control and Prevention in Atlanta, expressed caution about Dr. Webster's remarks. Scientists "would love to know why some patients develop more severe forms of SARS than other patients," Dr. Gerberding said, but "it is preliminary to ascribe that to the virus." C.D.C. scientists have identified the SARS virus in 7 of 39 probable SARS cases in the United States. But that "is much too small a number to draw conclusions about the virulence" of different strains of the virus, Dr. Gerberding said. Scientists in Canada, the United States and other countries have sequenced, or mapped, the basic molecular units of the SARS virus. The viruses mapped in the United States and Canada were from two patients and are virtually identical, Dr. Gerberding said. But she said that scientists needed to map viruses identified from more SARS patients before they could say whether any differences in the molecular structure of different strains could account for variations in severity among SARS cases. The molecular structure of the coronavirus class consists of a single strand of RNA that often makes mistakes as the virus replicates, allowing it to mutate and even recombine with other viruses. But Dr. Gerberding said that the C.D.C. did not have any evidence now to say whether the SARS virus was mutating. Dr. Gerberding said that her agency was not characterizing certain strains of the SARS virus as more or less severe than other strains because so many factors other than virulence are involved in determining the severity of an infectious disease and its death rates. One such factor is the health of the infected individual. Among the questions scientists are seeking to answer are: Do people with SARS have risk factors that increase the hazard of being infected with such a virus? How strong are their immunological defenses? Do they smoke? "We have a lot to learn," Dr. Gerberding said. The reason the United States has so few SARS cases and no deaths from the disease appears largely to be "the good luck that we have not had the right combination of someone who is highly infectious and inadequately protected health care personnel," Dr. Gerberding said. The C.D.C. has sent three experts to Toronto because the Canadian government requested "a fresh set of eyes" to determine if there are flaws in the infection control measures that health officials, doctors, nurses and other health workers are using against the epidemic there. The concern is that its spread is continuing to affect health workers despite what appears to be proper use of masks, gowns, gloves and goggles. The team includes a health care epidemiologist, an occupational health and safety expert who is knowledgeable about the use of masks and other ways to protect airway spread, and an environmental engineer knowledgeable about air systems. Dr. Gerberding said that based on her experience as an infection control expert at San Francisco General Hospital, it would be standard practice for such a team to review the use of masks and the ventilation of hospital rooms. Health workers are advised to wear special N-95 masks at all times in caring for patients. The masks are capable of filtering tiny viruses. But to be fully protective, such masks must fit tightly to prevent air leaks. With SARS, health workers probably need to adhere 100 percent to infection control measures "because there appear to be a number of patients who are highly infectious," Dr. Gerberding said. "Any leakage around the mask negates the whole value of having that filtration in front of your breathing zone." The team also would be expected to check on the adequacy of engineering precautions to make sure that the circulating systems in negative pressure rooms are not blowing air out of the room instead of preventing its escape. -- The silver-list is a moderated forum for discussion of colloidal silver. Instructions for unsubscribing may be found at: http://silverlist.org To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
