Since it first surfaced in China in November, the new pneumonia-like illness known as SARS has spread quickly around the globe, infecting more than 2,600 people and killing 98. The United States Monday increased its number of cases to 148 but no deaths have been reported in the country.
"This is the beginning of a problem," Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, said as she testified before the Senate Health, Education, Labor and Pensions Committee.
"We may see further spread of the disease in this country," Gerberding added.
This is in part because of so-called "superspreaders," or people who appear to be especially contagious after contracting the illness and could infect several other people, she said.
The future course of SARS is uncertain, Gerberding said. It could turn out to be a seasonal illness similar to West Nile virus or there could be a leveling off after the initial cases of infection.
"We don't know where this is going to go," she said.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases -- a component of the National Institutes of Health -- agreed the future of the disease was unpredictable.
"For that reason, we have to take this very, very seriously," Fauci said.
His agency already has begun initial work on developing vaccines and other treatments against SARS, which is believed to be caused by a new form of coronavirus. Known members of this family of viruses cause conditions such as the common cold and generally mild respiratory illnesses.
Researchers plan to have finished sequencing the entire genome of the new virus by this weekend, Gerberding said. That could aid attempts at finding drugs effective against it.
They also are developing diagnostic tests that will detect the presence of the virus and help identify those who have contracted it.
So far, no currently available medications have shown much promise for treating the disease. Some reports have indicated the antiviral drug ribavirin might be beneficial, Gerberding said, adding, "Increasingly, we are a little pessimistic that it's going to be an effective drug."
Officials now have a better picture of how the disease progresses. After exposure, it could take two to 12 days to develop symptoms. At first, people feel tired and have muscle aches, sore throat, fever and a headache, Gerberding explained. Then the fever goes away and is followed by coughing, chest pain and difficulty breathing.
Most people will recover, some might have to be put on mechanical ventilation and a small number -- about 4 percent -- will die.
Those developing early symptoms who have traveled or had close contact with travelers should see a physician, Gerberding advised.
Other steps people can take to protect themselves include avoiding travel to affected areas, particularly Hong Kong, Hanoi, Singapore and China, she said. "Unless you have to go, defer your trip," she said.
Health officials have the greatest concern about China and Hong Kong, said Dr. David Heymann, executive director of communicable diseases for the World Health Organization.
Hong Kong continues to report the most new cases, and in China the number of infected continues to increase in the Guangdong province -- where SARS is thought to have originated last November -- and there are indications other provinces likewise are affected, he said.
Last week, the Chinese government, which initially resisted help from outside health officials, pledged to be more cooperative. If they had implemented measures last November to control the spread of the disease, Heymann said, "the disease might never have spread."
Although in some of the Asian countries hardest hit by the virus, people now are wearing surgical masks, Gerberding said the precaution probably is unnecessary. The masks might help limit the spread of the disease from an infected person to a close household contact but, "beyond that, we are not recommending masks for anybody at this time," she said.
Commenting on the executive order issued by President Bush last week adding SARS to the list of diseases for which health officials can forcibly quarantine people, Gerberding said, "Right now, we're not quarantining anybody in the United States, and we're not planning to."
She added, "It is a precautionary, a 'just in case' kind of executive order."