Outbreak of SARS Waning

Three months after the SARS virus began its erratic and lethal hop around the globe, the outbreak of the enigmatic illness appears to be nearing an end.

New cases of the disease worldwide have dropped to an average of just seven a day, sharply down from an average of 149 cases a day in early May when the virus was still raging full force. Deaths from SARS are also down dramatically.

The trend suggests that an epidemic that once seemed hopelessly out of control a few weeks ago has been largely contained -- at least for this season.

“If you had told me two months ago that it would have been possible to put the genie back in the bottle in some places, I would have said, ‘That’s not how nature works,’ ” said Arnold Monto, professor of epidemiology at the University of Michigan.

Epidemics that spread across wide geographical areas and affect thousands of people have rarely been stalled so effectively, he said, particularly without the help of a vaccine to immunize at-risk populations.

There are still lingering uncertainties about containment of severe acute respiratory syndrome because of sporadic outbreaks in Toronto and Taiwan. The continuing flare-ups suggest that SARS remains a tenacious adversary that could spread across the globe again.

Some experts also view the sharp decline in cases reported by Taiwan and China with some skepticism. China reported a net gain of no new cases so far in June, and only nine deaths, compared with 1,868 cases and 173 deaths during May, according to World Health Organization figures. Taiwan has reported at least 15 new cases in June, and no deaths -- after a calamitous May, during which 80 Taiwanese died from SARS.

“People are wondering if the abrupt change is real,” or due to reporting irregularities, said Henry L. Niman, a virologist at Harvard Medical School.

SARS has already disrupted the economies of China, Canada and other nations, providing powerful incentives to declare victory as soon as possible.

But even cautious experts believe that the worst of the current crisis may be over. They credit aggressive public-health screenings and sometimes draconian quarantines as having dramatically curtailed the spread of SARS.

Singapore deployed in-home surveillance cameras and levied stiff fines on violators. That nation has reported no new SARS cases or deaths since May 20. In Beijing, where the caseload has also plummeted, SARS clinicians are housed in isolated dormitories instead of going home at night.

The rapid spread of SARS was likely caused by a few extraordinarily contagious “super spreaders.” But paradoxically, most victims are less contagious than a person suffering from a common cold.

“The good news is that this virus doesn’t transmit very effectively,” Monto said.

Studies have shown that the disease normally spreads only through close contact, and on average a SARS sufferer infects only 1.4 others. A transmission rate of 1, in which each infected person spreads the disease to only one other, usually guarantees that an infection will eventually die out, Monto said.

SARS has also been largely contained in Vietnam. It also appears to be under control in Hong Kong, once the epicenter for the international spread of the illness.

Currently, the WHO has travel advisories in place for Taiwan and five areas in China. The advisories recommend that travelers consider postponing all but essential travel to the areas.

Overall, SARS has infected 8,445 people and killed 790. The worldwide epidemic peaked in late April and early May -- during a two-week period, 2,780 new cases and 132 deaths were recorded.

Strict Measures Worked

Experts said that by that time, stringent screenings at points of transit, isolation of suspected cases and harshly enforced quarantines and social controls finally began to overcome the spread.

From then on cases plummeted, down an average of nearly 50% per week, to a total of only 43 cases in the last week. Deaths also declined dramatically; 18 were recorded in the last week.

If trends continue, the eradication campaign would be a public health triumph. Worldwide cooperation among health authorities and vigilance by screeners and clinicians have combined to identify and isolate victims, WHO officials said.

“In terms of the number of cases, we are seeing the end of the outbreak,” Hitoshi Oshitani, a WHO infectious disease official, told Reuters on Thursday.

The United States has remained relatively unscathed by SARS, with only 70 probable cases and no deaths despite busy air-travel routes to hard-hit areas. But officials said they would continue their watchful approach.

“We feel very lucky, but we are clearly not letting down our guard at this point. We have our full emergency operations center in place,” which closely coordinates among local, state and federal health authorities, said Daniel B. Jernigan, a medical epidemiologist for the U.S. Centers for Disease Control and Prevention.

An exception to the good news has been Canada, where there has been 50 new cases in June, most of them in Toronto.

“Why Toronto has struggled as much as it has -- we don’t really know why,” said David Brandling-Bennett, a WHO official with the agency’s Pan American Health Organization.

It may have started with simple bad luck. The spread of SARS was traced to a victim who infected 13 guests at the Metropole, a Hong Kong hotel. Their journeys to distant cities are blamed as the spark that turned a local Chinese epidemic into a worldwide scourge. One of those 13 traveled to Toronto, and proved to be a super spreader.

Experts said that unraveling the mysteries of the SARS virus will determine whether the disease is on the road to eradication or will reemerge in an annual cycle of illness.

Similar to the Cold

The SARS virus is spread primarily through coughed or sneezed droplets, like the common cold. Also similar to the cold or flu, SARS may naturally wane during summer months, then flare up during fall and winter, when weather drives people indoors and close quarters increase the rate of transmission.

Chinese researchers believe SARS was first transmitted to humans last year from the weasel-like civet or other wild animals that are sold as culinary delicacies in parts of China. But it may have established a reservoir of infection in people who do not necessarily become ill with full-blown SARS. Niman said Toronto’s latest cases may have been spread by such carriers.

If so, future outbreaks are likely.

“I’ve got a suspicion that the virus didn’t get stopped -- the disease got stopped,” Niman said.

Researchers also have yet to study mutations in the virus that may influence its lethality and resilience. But Chinese researchers reported a hopeful sign Thursday -- an antibody test that may become a fast and reliable way to diagnose the disease. Unlike earlier tests, it produced a very low rate of false-positive results. This may reduce the difficulty and cost of isolating suspected SARS cases that much later prove to be other illnesses.

The clearest lesson of SARS, experts agree, is that ignoring or minimizing an emerging disease -- as China initially did -- leads to disaster.

But urgent measures can work.

“We don’t regard ourselves as policemen,” Brandling-Bennett said. “We don’t like to act forcibly -- but we will if it’s required for public health.”