SARS usually begins with flu-like signs and symptoms — fever, chills, muscle aches, headache and occasionally diarrhea. After about a week, signs and symptoms include:

• Fever of 100.5 F (38 C) or higher
• Dry cough
• Shortness of breath

SARS is a serious illness that can lead to death. If you have signs or symptoms of a respiratory infection, or if you have flu-like signs and symptoms with fever after traveling abroad, see your doctor right away.

SARS is caused by a strain of coronavirus, the same family of viruses that causes the common cold. Previously, these viruses had never been particularly dangerous to humans.

Coronaviruses can, however, cause severe disease in animals, and that's why scientists suspected that the SARS virus might have crossed from animals to humans. It now seems likely that that the virus evolved from one or more animal viruses into a new strain.

How SARS spreads

Most respiratory illnesses, including SARS, spread through droplets that enter the air when someone with the disease coughs, sneezes or talks. Most experts think SARS spreads mainly through close personal contact, such as caring for someone with SARS. The virus may also be spread on contaminated objects — such as doorknobs, telephones and elevator buttons.

In general, people at greatest risk of SARS are those who have had direct, close contact with someone who's infected, such as family members and health care workers.

Many people with SARS develop pneumonia, and breathing problems can become so severe that a mechanical respirator is needed. SARS is fatal in some cases, often due to respiratory failure. Other possible complications include heart and liver failure.

People older than 60 — especially those with underlying conditions such as diabetes or hepatitis — are at the highest risk of serious complications.

Researchers are working on several types of vaccines for SARS, but none has been tested in humans. If SARS infections reappear, follow these safety guidelines if you're caring for someone who may have a SARS infection:

• Wash your hands. Clean your hands frequently with soap and hot water or use an alcohol-based hand rub containing at least 60% alcohol.
• Wear disposable gloves. If you have contact with the person's body fluids or feces, wear disposable gloves. Throw the gloves away immediately after use and wash your hands thoroughly.
• Wear a surgical mask. When you're in the same room as a person with SARS, cover your mouth and nose with a surgical mask. Wearing eyeglasses also may offer some protection.
• Wash personal items. Use soap and hot water to wash the utensils, towels, bedding and clothing of someone with SARS.
• Disinfect surfaces. Use a household disinfectant to clean any surfaces that may have been contaminated with sweat, saliva, mucus, vomit, stool or urine. Wear disposable gloves while you clean and throw the gloves away when you're done.

Follow all precautions for at least 10 days after the person's signs and symptoms have disappeared. Keep children home from school if they develop a fever or respiratory symptoms within 10 days of being exposed to someone with SARS.

When SARS first surfaced, no specific tests were available. Now several laboratory tests can help detect the virus. But no known transmission of SARS has occurred anywhere in the world since 2004.

Despite a concerted global effort, scientists have yet to find an effective treatment for SARS. Antibiotic drugs don't work against viruses, and antiviral drugs haven't shown much benefit.