My bad.
Posted on 04/26/2003 12:54:19 PM PDT by Sweet_Sunflower29
The spread of SARS may be due to people who are vastly more infectious than most sufferers, Julie Robotham writes.
They are the wild cards in the epidemic. So-called "super-spreaders", who apparently infect others with the SARS virus much more readily than most patients, seem to be responsible for several regional outbreaks of the pneumonia-causing illness.
If it is true that some SARS carriers are hyper-infectious, that would be grim for the prospect of containing the disease. Just one super-spreader could ignite a whole new outbreak, and demolish all the good work done by isolating dozens of other patients.
What specialists must now do is figure out how real the phenomenon is. Is there something fundamentally different about how the coronavirus implicated in SARS is carried or shed by the super-spreaders, or did they just cough in the wrong place at the wrong time?
Esther Mok, a flight attendant, has been dubbed a super-spreader by the health minister of Singapore, which traces almost all cases in its epidemic back to 26-year-old Ms Mok's shopping trip to Hong Kong.
"Esther Mok infected the whole lot of us," the minister, Lim Hng Kiang, tactlessly told a press conference earlier this month. Ms Mok has survived, but her parents are both dead from severe acute respiratory syndrome.
The idea that one individual, who appears no different from any other patient, could be the touchpaper for an incendiary outbreak sounds like an urban myth. It sounds like a benighted explanation for something scary and not understood, justifying people's feelings of mistrust.
But other apparent super-spreaders have been identified. A Chinese doctor, who visited Hong Kong and spread SARS through a hotel there, is linked to multiple infections, including at least two who took the disease out of the territory and introduced it to other regions of the world. Experts are far from dismissing the possibility that some patients may be off the scale in their capacity to pass on the virus.
Julie Gerberding, director of America's Centres for Disease Control, this week nominated the relative infectiousness of different individuals at the top of her wish-list of questions requiring answers. "Why are some patients more infectious or more capable of serving as a source of infection to others than most patients are?" she asked. "How long does a person remain infectious after they acquire the illness?"
Scientists have to entertain a range of possibilities. It could be that some individuals are somehow - possibly genetically - extremely susceptible to becoming ill from or spreading SARS. Perhaps some people are capable of sending the virus into the air around them, while most transmit it only directly through nasal or throat secretions.
Alternatively, it could be that the super-spreaders are carrying a mutated form of the virus that makes it easier to contract.
Associate Professor Bill Rawlinson, a senior medical virologist at Sydney's Prince of Wales Hospital, says a basic test to determine that someone has SARS will offer no information about their infectiousness. But other viral illnesses may provide some clues.
"To get a viral infection you don't just have to be in contact with the virus, you have to contact enough of it," Professor Rawlinson says. Just one viral particle in a thousand "droplets" in a cough or sneeze probably will not be enough to infect another person, he says. But increase the concentration and you reach a threshold, after which the chance of passing on the bug jumps rapidly.
There are other general rules. "If you're a child you tend to have more virus and be more infectious," he says. The same goes for people whose immune systems are suppressed by HIV infection or drugs.
The "viral load" - the number of live copies of the virus a person carries - also changes during the course of an illness. "If you're incubating or early in the virus, there often is large amounts present. There are even people who are asymptomatic carriers. You can find influenza in people's throats who have no symptoms. They can be asymptomatic of genital herpes [virus] without lesions," Professor Rawlinson says.
To date, that does not seem to be the case with SARS. "The epidemiology suggests SARS is most infectious when people are symptomatic," he says.
The question of whether there are more and less infectious SARS strains will not be answered until many more specimens have been analysed and compared. But this is the case with some other viruses. Influenza A, for example, is more infectious that influenza B.
The news on SARS infectiousness is both very good and very bad, Professor Rawlinson says. Where stringent control measures are in place, containment seems possible. Singapore and Canada appear close to reining in their outbreaks. But when procedures slip, SARS spreads like wildfire.
Dominic Dwyer, a medical virologist at Westmead Hospital, says: "Certainly it does appear there have been people who are 'super-spreaders' in the sense that they have infected lots of people around them."
What is hard to know, he says, is whether they are genuinely more infectious, or whether they just happened to come into contact with more people.
His gut feeling is that the truth may fall in the middle, with individual variations in the degree of infectiousness at least partly responsible. Dr Dwyer does not dismiss the concept of the super-spreader. In other illnesses, he says, "some people have a lot of virus on-board; others don't".
SARS may be a more extreme example of that.
In blood-borne viral diseases, like HIV, it is possible to test for the concentration of virus. That in turn is assumed to be linked to the amount of virus shed through other body secretions and to the likelihood the infected individual will pass it on.
In viral respiratory infections, such as flu - and presumably SARS - the picture is much hazier.
A test on the products of one cough might yield nothing, but a slightly more energetic one a minute later could be saturated with virus. "We don't have a good handle on viral load and shedding in respiratory illnesses," Dr Dwyer says.
That fact is going to make the SARS puzzle all the more difficult to solve.
Stick your head back in the sand now
I am sure they will finish in time for the worse to be over
secondly, China has a literacy rate of well over 87%. OK, just as an example, they are trainning and producing well over 500,000 IT engineers and IT workers every year.
Ugggh we are dealing with a human virus, not a computer virus.
I am not going to argue with ignorance anymore.
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