The fast-spreading severe acute respiratory syndrome virus, or SARS, causes flu-like symptoms including fever, chills, headaches and body aches, and, in some cases, patients suffering from the illness reported having serious difficulty breathing.

Scientists at the U.S. Centers for Disease Control and Prevention, one of the organizations investigating the illness, believe the virus originated in China, where more than half of all the cases have been reported.

In the United States, doctors have reported 149 cases of the illness but no deaths.

What is SARS?

One of the main concerns for scientists is the virus' failure to respond to antibiotics. Although studies now show that a new variety of the group of viruses known as coronaviruses may be the cause of SARS, patients given antibiotics, steroids and antivirals have not shown a positive response to treatment.

Also of major concern is how SARS is spread. According to the CDC, people infected with SARS spread the virus by coughing or sneezing droplets of fluid into the air. Those in close proximity to the SARS carrier breathe in the droplets and can get sick. The common cold virus, also a member of the coronavirus family, is spread in the same fashion.

Health officials first noticed SARS in late February in the Guangdong Province of Southern China. Chinese officials reported 31 deaths from the disease that month. Since then, 361 new cases appeared in Guangdong in March alone.

Working closely with Chinese authorities, World Health Organization experts are in the province investigating how the disease is spread and looking for ways to control it.

Who has been affected?

Eighteen countries have confirmed cases of SARS, including Spain, Germany, France, Italy, Australia, Britain and Romania. The disease has been spread mainly through air travel to Asia, health officials say. In the highest death toll outside of Asia, Canadian officials reported 10 deaths caused by the virus.

The disease has hit Asian countries hardest. In Hong Kong and Singapore, carriers of the virus have been quarantined against their will. Officials in Singapore closed schools because of parental concerns, and in several countries, people do not leave home without medical masks.

Although Chinese Premier Wen Jiabao said his country is capable of facing the crisis and welcomed international tourists, World Health officials have issued a travel emergency, recommending that travelers postpone trips to China and Hong Kong until scientists know more about the virus and how to treat it.

Going forward

On Friday, President Bush issued an executive order allowing the forced quarantine of patients in the event of a severe outbreak in the U.S., restricting the movement of those carrying the virus.

Although the World Health Organization is reporting new cases of SARS every day, officials expect a majority of the virus' sufferers to recover after hospitalization and intense treatment.

-- By Kristina Nwazota, NewsHour Extra