Re: H1H1 Super Spreader in India?
Can Some Individuals Transmit SARS More Widely Than Others?
Wall Street Journal - April 10,
2003
Trish Saywell, Staff Reporter of The Wall Street Journal
--------------------------------------------------------------------------------
Top disease specialists are debating the theory of whether some people with SARS might be
"superinfectors" or "superspreaders" -- that is,
unusually contagious and able to transmit the illness to larger numbers of people.
Robert Breiman, head of a World Health Organization team investigating severe acute respiratory syndrome in China's Guangdong province, said
one patient with the virus spread the disease to more than 30 people, two of whom died.
He recovered, but only one of the 30 people he infected went on to transmit the illness, and that person infected just two others, who didn't pass it on to anyone else. "There are stories like that," Dr. Breiman says. "We're hoping to get them to look more closely at superspreaders."
Singapore Health Minister Lim Hng Kiang used the term in describing a Singaporean woman who contracted SARS at Hong Kong's Metropole Hotel as one of several "superinfectors."
Her infection triggered a chain reaction that sickened 50 family members, friends and close contacts, along with 56 health-care workers, and led to several deaths, including those of her parents, according to Singapore's Ministry of Health.
The woman was one of three Singaporeans who contracted the malady at the hotel, but the only one of the three who appeared to have transmitted the disease to others.
"They all got it from the same source but two of them didn't cause a lot of problems while the third one did. I don't think it's totally happenstance," says
Henry Niman, a Harvard University instructor in surgery at Massachusetts General Hospital in Boston who has studied retroviruses.
Dr. Niman argues the number of superinfectors is low as a percentage of the total SARS population and that they "stick out like sore thumbs."
While he concedes he doesn't know what would make superinfectors so infectious, he speculates it could be any number of reasons, including that they have a variant of the virus or shed more of the virus than others.
What is the medical evidence? Julie Gerberding of the U.S. Centers for Disease Control and Prevention says the Atlanta agency is looking into the notion. "It may be that certain individuals are more efficient at transmitting the virus than others, and that is a matter of chance or other factors that we haven't figured out yet," she told reporters.
What is known is that a person is most likely to be infectious when they have symptoms of the sickness, such as a fever, aches and cough. It also appears that people are more infectious when they become more seriously ill. In Toronto, physicians believe that one patient spread SARS to 20 or 30 people in a short period of time.
Toronto's outbreak, the biggest in any city outside of Asia,
accelerated largely because of one such spreader who was treated at Scarborough-Grace Hospital on March 16 and 17
without respiratory precautions, said Colin D'Cunha, Ontario's public-health commissioner.
Doctors still are trying to piece together links among all of those who got sick at the Toronto hospital. Some appear to have contracted the malady without ever coming into direct contact with SARS patients, raising the specter of airborne, rather than droplet, transmission in rare cases, says Allison McGeer, director of infection control at Toronto's Mount Sinai Hospital and a consultant at Scarborough-Grace.
Such a spread could be explained if some patients were more infectious than others, she said. Dr. McGeer says she doesn't believe the virus spreads by lingering on surfaces, such as elevator buttons.
"This is not a physical structure thing," she says. So far, there have been more than 2,900 suspected cases of SARS world-wide, mainly in Asia, with at least 106 deaths. Although the U.S. has about 150 suspected cases, there have been no deaths from the disease, which is believed to be caused by a new variant of the coronavirus.
Some medical experts contend the superinfector idea is misleading. Their seemingly higher transmission rate could simply be because of circumstances such as having contact with greater numbers of people while in the most-infectious stage or to practicing poor hygiene and not covering mouths or noses when coughing and sneezing.
"
There's no definite evidence that there are superspreaders in SARS," says David Bell, a public-health physician with the WHO in Manila. "
It's very difficult to prove that one person is putting X amount of virus particles out and the next one isn't putting as many virus particles out."
Nonetheless, Dr. Bell says the
jury is still out and "it's possible" some people spread the SARS virus more efficiently than others. "We can say that there appears to be some people who have spread the infection to a lot of others. But we can't say whether they are intrinsically different or whether they've been in circumstances that have promoted that spread," he says.
People could spread more viral agent than others if their immune systems are suppressed or compromised by diseases such as HIV, or severe kidney and liver disease. For other SARS watchers, it is more a matter of actions and bad timing that could make some people seemingly more infectious than others.
"There is no such term [as superspreaders] in medicine," says Stephen Berger, an infectious-diseases expert at the Tel Aviv Medical Center in Israel. "There are people who by circumstance can transmit it more easily than others. If you have a person with HIV who runs around doing things he isn't supposed to, then he's going to become a superinfector."
Dr. Berger says everyone may have the same opportunity at some point to infect other people to a high degree. For instance, with chicken pox, "everybody is a superinfector when they go through the most-infectious stage of the disease," he says. People also may have an infectious disease and be virus carriers without symptoms, he says.
They may even feel well enough to stick to their normal daily routines and become "ticking time bombs," who could easily fall under the definition of a "superinfector," he says.
--David Murphy and Elena Cherney contributed to this article.
Write to Trish Saywell at
trish.saywell@wsj.com
http://www.aegis.org/news/wsj/2003/WJ030406.html
