Posted on 04/26/2003 7:49:41 PM PDT by Prince Charles
Super-spreaders fan SARS fears
By M.A.J. McKENNA
The Atlanta Journal-Constitution
Health authorities are watching uneasily for an event that could reverse their apparent success in containing the U.S. outbreak of severe acute respiratory syndrome: the arrival of a so-called super-spreader.
There are 41 probable cases of SARS in the country, and only two sufferers were infected by other Americans. In Asia and Canada, by contrast, clusters of 20, 50 and more than 100 cases have been caused by single highly infectious individuals.
A 26-year-old Singaporean infected more than 100 people -- including her parents, grandmother, uncle, brother and pastor. A 48-year-old businessman passed SARS to 80 health care workers in Hanoi, Vietnam, causing the death of WHO doctor Carlo Urbani. A 26-year-old Chinese man gave the disease to 112 doctors, nurses and medical students in a Hong Kong hospital.
A SARS sufferer who infected fellow passengers on an Air China flight may have spread the disease to Taiwan, Beijing and China's interior. And every case so far recognized in Toronto can be traced, through multiple generations of infection, to a 78-year-old grandmother who brought the disease from Asia and became the first person in Canada to die of SARS.
Yet it appears that no super-spreaders have come to the United States.
"We have been fortunate we haven't encountered such a person," said Dr. James Hughes, director of the National Center for Infectious Diseases at the Atlanta-based Centers for Disease Control and Prevention, "but that could change at any moment."
Is it virus or patient?
Not enough is known about the virus that causes SARS -- a newly recognized coronavirus, from a family of viruses that cause mild respiratory infections in humans and more serious illness in animals -- for researchers to be able to pinpoint what makes an individual highly infectious. It could be a difference in the virus, or in the patient. It could be caused by two infections occurring at once, or by a third factor such as the environment.
In some respiratory diseases, the location in the body where an infection takes hold -- high up in the throat, or deep in the lung -- can change how much virus the patient coughs out. In one experiment on record, patients who already had bacteria in their systems became more infectious when they were secondarily infected with a virus.
And in rare cases, patients have been extremely infectious, even though they shed the usual amount of virus, because they shed it for a longer than usual amount of time.
That appears to be happening in Hong Kong, particularly in the Amoy Gardens apartment complex cluster -- more than 300 cases, apparently caused by one man, that may be connected to the virus's surviving in sewage.
"There is information out there to show that virus is shed for a very long time by some people -- weeks as opposed to days," said Dr. Robert Webster of St. Jude's Children's Research Hospital in Memphis, an internationally known virologist who was asked to consult on SARS by the government of Hong Kong. "Some of the people in the Amoy Gardens estate were moved out into quarantine [for 10 days], and then allowed to go back to work, and found to be still shedding virus."
The man who caused the Amoy Gardens cluster was already a hospital patient: He was receiving outpatient treatment for kidney disease, which included drugs to suppress his immune system. That could be a recipe for creating a super-spreader, experts said: With no immune response to hold its replication in check, the virus could multiply and shed from the body in vast amounts.
Seeking genetic clues
As they search for the key to super-spreaders, some scientists are looking to the virus itself. A half-dozen examples of the virus, from different parts of the world, have been genetically unraveled by laboratories. No two are exactly alike.
"I think the mutations are going to provide the mechanism for the super-spreader phenomenon," said Dr. Henry Niman, a Boston virus researcher who runs an e-mail discussion group on SARS that early on alerted participants to super-spreaders. "There is enough data now to say the mutations are real, and not sequencing errors."
However, other researchers say it is too soon -- in the lab science of SARS, and in the disease's emergence among humans -- to pin the super-spreader problem to any particular genetic finding.
The SARS virus is an RNA virus, meaning that it has a single strand of genetic material rather than the familiar double-stranded ladder of DNA. Such viruses make many more "copying mistakes" as they reproduce themselves. A disease organism is likely to make many such small changes when it adapts to a new host, as SARS is doing in humans. It is the virus's way of finding its most advantageous niche.
"Of course there are going to be differences," Webster said. "Most of the differences will be background noise, but every now and again, one of those changes is going to make a world of difference."
The unpredictability that super-spreaders bring to the expanding epidemic poses a challenge not just in bracing for the continuing spread of SARS, but in predicting its future. To forecast what might happen, a task called modeling, researchers must assume that a case of SARS passes on the disease to an average number of people, called the basic reproductive number.
If the basic reproductive number is less than one, the disease will decline over time, because each generation of cases will be slightly smaller than the one before. If the number is more than one, each generation of cases will be larger than the previous one and the epidemic will expand.
But if the number cannot be averaged, modeling the disease's future -- and anticipating moments when public health or medical interventions could change its course -- becomes more difficult.
"If someone can easily infect 12 people, or 60, then that creates a heterogenous pocket of transmission where the disease can continue to spread," said Dr. Elizabeth Halloran, a professor of biostatistics at Emory University's Rollins School of Public Health who has modeled the spread of other diseases, including smallpox. "You could say that the chain is as weak as its strongest link."
Possibility of respite
As they watch for the emergence of additional super-spreaders, health authorities are hoping for an uncertain ally: the weather. On Friday, WHO officials advanced a hypothesis that SARS will become a seasonal disease, similar to other respiratory infections such as influenza.
If that hypothesis is correct, SARS transmission should die down as the weather warms in North America and Europe, giving scientists a respite in which to intensively research the new disease. One urgent investigation will look for any viral material from the outbreak's earliest days in China's Guangdong province last November, perhaps preserved in biopsy or autopsy material or swabs from patient exams.
"One question will be how much variation there is in the genetic sequences identified in different parts of the world, and how those trace back to the original source patient or patients," Hughes said. "An important question is how rapidly this virus evolves over time, because that will have implications for vaccine development in particular."
Typhoid Marys, one and all.
Not enough info here. Were they tested at the beginning of the 10 days, or could they have caught it while in quarantine? And if they were shedding virus at the beginning, why were they put into a camp with many others?
Have there been any cases that we know of that were HIV/AIDS carriers and then got SARS?
BTW, they should come up with a different name than "Super-Spreaders" -- it sounds too much like the magazine section of the Clinton presidential library.
You come up with a new name, I'll use it.
Flu geneology. Neat idea. Let's see how that would work, like this, I was infected and died by 10,003-160,000. Something like that?
Another mystery bug kills 38 children in Vietnam
AN unidentified illness - which health officials say does not appear to be linked to SARS - has killed 38 children and sickened more than 60 others in 17 Vietnamese provinces during the past three months, state-controlled media reported yesterday.Doctors and medical experts, along with the World Health Organization, completed an epidemiology survey in Ho Chi Minh City on April 15. They did not classify the illnesses as an outbreak because the cases did not appear to be linked and were scattered throughout many provinces, the newspaper said.
All the children who succumbed to the disease experienced symptoms of high fever and convulsion. Nearly 70 per cent died within a day of becoming sick. The disease is suspected of being part of the enterovirus group, the Pasteur Institute in Ho Chi Minh City said.
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