WHO: SARS cases over 2,400
Cases now in 18 countries
GENEVA, Switzerland (CNN) -- As of Saturday, 2,416 cases and 89 deaths attributed to severe acute respiratory syndrome, or SARS, have been reported from 18 countries, the World Health Organization said.
That represented an increase of 63 cases (2.7 percent) and five deaths (6.0 percent) in the past 24 hours.
There were three newly reported deaths in Hong Kong and one in Singapore, and the first case in Malaysia also died.
Five new cases were reported in Canada, 39 in Hong Kong, two in Taiwan, one in Singapore, and one in Britain. One of the two cases that Switzerland had classified as "probable" was removed from the list.
More than 100 cases in U.S.
The news came the day after U.S. health officials said the mystery respiratory illness that originated late last year in China has affected 115 people in the United States, up from 100 Thursday.
Nearly all the patients, 109, had traveled to those regions of Asia where SARS is entrenched, said Dr. James Hughes, director of the National Center for Infectious Diseases at the Centers for Disease Control and Prevention in Atlanta, Georgia.
Four are close contacts of SARS patients and two are health workers who cared for SARS patients.
Of the 115, 43 have been hospitalized at some point during their bouts with SARS, 27 are currently hospitalized and 27 have shown evidence of pneumonia, Hughes said.
But none of the U.S. cases, which are spread across 29 states, have been fatal, he said. "I think we've been lucky."
Hughes acknowledged that some patients may have been missed and that it is possible secondary transmission is occurring underneath the health investigators' radar.
But, he said, "everybody is sensitized. If such clusters are encountered, we'll be testing them for evidence of the virus.
"We can't totally close our minds to that possibility, but there's no evidence of that so far."
Among efforts to control the spread of SARS is the practice by quarantine officials meeting planes returning directly or indirectly from SARS-affected areas -- Indonesia, Vietnam, Singapore, mainland China and Hong Kong.
So far, more than 1,000 flights have been met and more than 250,000 health-alert notices have been distributed, he said.
The CDC is also exploring the possibility of developing an in-flight education video for passengers and working on streamlining the process for getting a copy of a plane's manifest so officials can contact passengers who may have been infected on a flight.
Bush signs quarantine order
President Bush signed an order Friday adding SARS to the list of diseases for which people can be quarantined.
The CDC has deployed about 20 investigators overseas to work on the outbreak. The disease agency is participating in an international network of 12 laboratories in 10 countries that are working to determine how to stem the outbreak.
Evidence is mounting in support of the finding by a number of the laboratories that a previously unrecognized coronavirus, the group of viruses that cause of the common cold, could be behind SARS, Hughes said.
Specimens from a number of patients have yielded positive test results for the coronavirus, Hughes said.
Experience still suggests that most of the transmission occurs by droplets, which requires standing three to six feet from an infected person, Hughes said.
But the mode of transmission remains unproven and researchers are keeping "an open mind," he said.
The incubation period -- the time between exposure and onset of symptoms -- is believed to be two to seven days, though a range of one to 12 days is possible, he said. "That will be refined better as more testing is done."
Asked whether the outbreak could wind up becoming a global pandemic, Hughes said. "We're not totally on top of this by any means. I don't [make predictions], but we have to stay ahead of this and treat this as the urgent global public health threat that it is."
Researchers arrive in China
After weeks of delay, a team of researchers arrived Thursday in China's Guangdong province, where officials believe the outbreak started last November.
"The cooperation has improved dramatically," Hughes said.
Health and Human Services Secretary Tommy Thompson spoke Thursday with China's minister of health. "I'm optimistic that, in part as a result of that conversation, that cooperation will be there," Hughes said.
A number of efforts are under way to fight the disease.
Federal researchers are working to see whether any of a broad range of antiviral agents proves effective against the disease.
Clinical evidence suggests that one antiviral, ICN's Ribavirin, "has some effect," Hughes said. "We're anxious to see how it looks in cell culture, in the test tube."
One doctor in Hong Kong has reported treating patients with serum taken from other SARS patients who have recovered. The idea is that the patients would have developed the antibodies necessary to halt the virus' replication.
"He had some evidence to suggest that there might have been some response there," Hughes said.
And on Thursday a pharmaceutical industry trade group held a teleconference with federal agencies to discuss issues related to drug and vaccine development.