Virus Called Mostly Under Control

By LAWRENCE K. ALTMAN, The New York Times, April 12th 2003

A month after the World Health Organization issued its first global alert about an epidemic of a mysterious new respiratory disease, the agency said yesterday that the epidemic appeared under control in most countries, although too little was known about its spread in China.

The organization said the epidemic had peaked in Guangdong Province of China, the region where the disease, known as SARS for severe acute respiratory syndrome, is believed to have appeared for the first time, in November.

The global alert was effective because it allowed countries that had SARS cases imported from Asia "to immediately contain the threat of local transmission in their own populations," said Dr. Mike Ryan, a medical officer for W.H.O.

" As of today, we believe that countries are being successful at containing the virus, but that does not mean that the outbreak is over," he said according to a transcript of a news conference in Geneva where the organization, a United Nations agency, is based. "All cases in the past three weeks that have been imported to other countries have been adequately isolated and contained, and no further local transmission has occurred."

The cause of SARS is unknown, although W.H.O. scientists strongly suspect it is caused by a previously unknown member of the coronavirus family.

The organization issued its alerts on March 12 and 15 out of deep concern that SARS appeared to be the first severe and easily transmissible new disease to emerge in the 21st century.

As is standard in investigating outbreaks, epidemiologists map the occurrence of cases in what are known as epidemic curves. Those in the SARS epidemic show a continuing daily decline in the number of new cases since their peak. "That means that the outbreak is being contained, but whether it will be 100 percent contained and stopped is not clear," said Dr. David L. Heymann, executive director of communicable diseases for W.H.O.

The main caveat in the health organization's guarded optimism is China, Dr. Heymann said, because SARS cases continue to occur in Guangdong and "we don't know what's going on outside of Guangdong Province, and that is our concern."

Another major concern is Hong Kong, which has experienced the second-largest outbreak, behind mainland China. Cases in Hong Kong continue to be reported among health care workers, and hospitals have been overwhelmed with patients. Schools are closed until April 21. Health officials have been deeply troubled by a large outbreak at the Amoy Gardens apartment complex in Hong Kong. But yesterday W.H.O. said that stringent public health measures appeared to have controlled the Amoy Gardens outbreak.

There have been 1,290 cases reported from mainland China since November and 998 in Hong Kong since Feb. 1. Why Hong Kong, with its much smaller population, should have been hit so severely is not known. Dr. Ryan speculated that the difference might lie in Hong Kong's dense population and the possibility that the SARS agent was spread on contaminated objects there.

Passengers on airplane flights have greatly aided the spread of SARS through the world, health officials say. Most passengers became ill after they arrived at their destination, but some seem to have transmitted SARS to passengers seated next to them or in the two rows in front or behind them. "The virus has not circulated within airplanes to a wide number of people within airplanes and we have no reason to believe that it is circulating in airports," Dr. Heymann said.

W.H.O. has recommended that people on nonessential business not travel to Hong Kong and Guangdong Province. The reason, health officials said, is less because of possible transmission on flights than on the risk of being exposed in those areas. Dr. Heymann said that the organization would soon consider revising that recommendation.

W.H.O. also said that because no human infections had resulted from contact with goods, products or animals shipped from SARS-affected areas, such items arriving from affected areas do not appear to pose a risk to public health.

Though Dr. Heymann was largely optimistic in his remarks, he cautioned that "we still don't know yet whether this disease will become an endemic disease, like tuberculosis, like malaria, or whether by the intensive containment activities that are going on throughout the world, this disease will be driven back into nature."

One reason for the optimism was that transmission from an imported case had occurred in only 6 of the 21 regions or countries in which SARS had been reported. They included Canada, mainland China, Hong Kong, Taiwan, Singapore and Vietnam. Dr. Heymann said he found it encouraging that there had been no large outbreaks within a country from imported cases after W.H.O. issued its global alerts.

Dr. James Young, Ontario's commissioner of public safety, said yesterday that "we're making great progress" in controlling SARS.

As of yesterday, W.H.O. had received reports of 2,890 SARS cases, including 116 deaths, for a 4 percent death rate. Of the survivors, 1,373, or 49 percent, were reported as recovered.

But, Dr. Mark Salter, a W.H.O. medical officer, cautioned that it was too soon to know how many, if any, of the SARS survivors would suffer permanent lung damage.

A perplexing feature of SARS is that about 80 to 90 percent of cases begin recovering about one week after onset of symptoms, which include fever of 100.4 degrees Fahrenheit or higher, malaise, dry cough and other respiratory symptoms. The remaining 10 percent to 20 percent worsen and require intensive care, and about half of the people among that group develop such severe breathing difficulty that they need to be attached to a mechanical respirator.

SARS deaths are usually caused by lung damage. But pathology studies show that the principal cause of the damage is not the SARS agent but the body's immune reaction against it, Dr. Salter said.

Most SARS cases have occurred among young adults, W.H.O. said, without defining the age limits. The reason appears to be the large number of health care workers who have come down with SARS. Relatively few children have been affected.

Scientists do not know how SARS originated. Chinese officials have suggested that the first case was in a businessman in Foshan, a small industrial city in Guangdong Province. But, Dr. Heymann said, scientists do not know whether all subsequent SARS cases can somehow be traced to that businessman or whether the later cases resulted from repeated new introductions of the SARS agent from some unknown source in nature, like an animal.

So far, scientists have found no evidence of the coronavirus in cockroaches, as some Hong Kong officials had theorized, or rats. The coronavirus can infect cats for a day or so, but cats quickly get rid of the virus and do not become ill.

Dr. Heymann said that the coronavirus that is suspected of causing SARS was first detected in Hong Kong by one of the 17 members of a collaborating network that W.H.O. formed to combat SARS. The virus was next identified by the Centers for Disease Control and Prevention in Atlanta and subsequently by all the other network laboratories.

Identifying a virus is only a first step toward proving that it causes a disease. The traditional criteria for proof come from fulfilling what are known as Koch's postulates. Scientists must complete the last two — determining whether injecting the virus into animals causes similar symptoms to what humans experience, and then recovering the virus from those animals and repeating the process in other animals. Those efforts are in progress, said Dr. Klaus Stöhr, the scientific director of the W.H.O.'s investigation.

There is no known effective therapy for SARS. Doctors in Hong Kong have tried injecting the plasma portion of blood from recovering patients in hopes that the antibodies they have formed will help other patients. The doctors who have used the technique have not reported striking findings. The treatment also can be dangerous, making a patient's condition worse.

In a different, apparently novel approach to such therapy, doctors in China have aerosolized the antibodies taken from recovering SARS patients and sprayed it among other sick patients. Doctors elsewhere said they had never heard of aerosolizing the antibodies. The results are not known.

Dr. Salter held out hope that a vaccine might be developed to protect against SARS because there are marketed vaccines to protect animals from infection with other members of the coronavirus family.