Researchers Shed New Light on Virus, ‘Super Spreaders’
A flurry of scientific papers released Thursday suggests that researchers are beginning to get a glimpse into the biology of the virus that causes SARS.
The new research confirms previous speculation that much of the lung damage from SARS results from an overactive immune system, and that there really are “super spreaders” -- latter-day Typhoid Marys who play a disproportionate role in the spread of the disease. It also suggests that the coronavirus that causes SARS is evolving relatively slowly and that there is no evidence more pathogenic strains are appearing.
Meanwhile, the World Health Organization has raised its estimate of the fatality rate from severe acute respiratory syndrome to about 15% -- and higher in the elderly -- bringing its official pronouncements more in line with research released this week suggesting a similar rate in younger people and a rate greater than 50% in those over age 60.
“The global estimate we had previously was always clearly an underestimate,” said the WHO’s Mike Ryan. “This is now much more accurate.”
The WHO also said Thursday that reports of relapses among 12 recovered SARS patients in Hong Kong were inaccurate. “SARS has not recurred in any of these patients,” said Dr. David Heymann. “These patients have been readmitted to the hospital, but with diseases other than SARS.”
In a paper published online by the international medical journal Lancet, Dr. Yuen Kwok-yung and his colleagues at the University of Hong Kong reported on the clinical progress of 75 SARS victims from the Amoy Gardens housing complex. All were given the standard treatment of the antiviral drug ribavirin, as well as immune-suppressing steroids.
Symptoms for most of the victims improved during the first week after admission, then worsened in the second week. Fever and pneumonia initially improved, but 85% of patients developed fever again after nine days; 73% had diarrhea, a much higher percentage than observed elsewhere.
X-rays showed that congestion in the lungs improved after about a week, but then got worse again in about 45% of patients. By the third week, one in five of the patients had developed acute respiratory distress syndrome, or ARDS, which required mechanical ventilation -- a worsening of the disease even though the victims’ bodies had apparently brought the viral infection under control.
Yuen said the severe lung damage seemed to be caused by the body’s immune reaction and not by the virus.
But Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention, cautioned that physicians should learn more about the disease before attempting to suppress this immune response. “It’s far too early to put patients at risk with speculative therapy,” she said.
Since the beginning of the SARS outbreak, researchers have speculated about the existence of super spreaders. One suspected case was Dr. Liu Jianlun, who stayed on the ninth floor of the Metropole Hotel in Hong Kong, where he infected at least 13 guests. Another was an American businessman who infected several health-care workers at a hospital in Hanoi before he died.
In Thursday’s Morbidity and Mortality Weekly Report, published by the CDC, Singapore researchers studied the disease’s spread in the early stages of the outbreak. They concluded that 81% of the victims did not infect anyone else, but that others were, indeed, super spreaders -- defined as having infected at least 10 people.
The team from the Singapore Ministry of Health concluded that five people infected at least 144 others, thereby having a major impact on the spread of the disease.
Unfortunately, the team could find no other characteristics to distinguish the super spreaders from other victims, and researchers are at a loss to explain the phenomenon.
“We can’t tell up front who is infectious and who is not,” Gerberding said. She noted, however, that many of the virus transmissions by the super spreaders occurred before effective control measures were in place.
In another online paper published by the Lancet, Dr. Edison Liu and his colleagues at Singapore’s Genome Institute reported that they had compared the genetic blueprints of several different specimens of the SARS coronavirus collected in Singapore, Hong Kong, Guangdong province and Beijing and concluded that they were remarkably similar.
In an editorial published with the paper, microbiologists Earl G. Brown and Jason A. Tetro of the University of Ottawa said “the results suggest a remarkable genetic conservation of the virus since the outbreak was first documented.”
That means, unfortunately, that the virus “is well adapted to the human host” and thus likely to keep spreading.
In other developments Thursday:
* The CDC reported for the first time the origins of probable SARS cases in the United States. Of the 63 cases, 36 had traveled to mainland China, 19 to Hong Kong, five to Singapore, three to Hanoi and seven to Toronto. Eight had visited two or more SARS-affected areas within 10 days before the onset of their symptoms.
* Three U.S. schools -- Case Western Reserve University in Cleveland, the University of Rochester in New York state, and Washington University in St. Louis -- have requested that families of students from SARS-affected areas not attend this year’s commencements.
All have significant numbers of students from Asia, and all promised to broadcast the commencements over the Internet so families could watch.