No, it wasn't the flu. It was SARS.
The end of 2003 saw hundreds of Americans sick with the flu and many others belatedly seeking the hard-to-find vaccine, but it was SARS that sickened 8,000 in Asia and Canada. The mysterious new virus, which came to worldwide attention in March, killed more than 800.
Now, SARS - even the acronym joined the workaday vocabulary with surprising speed - is in abeyance. Whether it will rebound during the winter as a deadly worldwide epidemic is the most worrisome of many questions that remain about the mysterious virus.
Unlike the flu, there is no vaccine to prevent severe acute respiratory syndrome and there is no medicine that can cure it.
It began in China's Guangdong province in November 2002, probably jumping from animals to people. But it did not spread until last February, when a man infected with the virus passed it to several other guests at a Hong Kong hotel. By the time the World Health Organization put out a global alert a month later, a worldwide epidemic was under way.
The health agency declared it under control in July, after it had spread to 29 countries.
"We were all relieved and somewhat surprised we were able to stop continued transmission of SARS and eliminate it in humans, as best we can tell, by the beginning of July," said Dr. Larry Anderson, respiratory virus chief at the Centers for Disease Control and Prevention.
Possible sources of renewed SARS: the same animals that spread it to humans last year; other species that have caught the virus since then, potentially even from humans; people with lingering infections, and stored virus that escapes from labs.
Health officials say the key to controlling SARS will be quickly identifying the sick and keeping them isolated so they do not pass it on.
SARS killed no one in the United States. But the flu, which has afflicted humans throughout history, kills on average 36,000 Americans every year. Experts worried this season's outbreak would be even worse.
The flu season began earlier than usual in Western states, and several children were among the first fatalities, while many more were hospitalized with serious complications. Potentially making matters worse, the strain circulating at year's end emerged too late for vaccine producers to include in their recipe for prevention.
Other infectious disease news of 2003 involved more exotic viruses. In June, an outbreak of monkeypox, mostly in Wisconsin, Illinois and Indiana, made about 70 people sick with fever and rashes. The outbreak was traced to prairie dogs that apparently caught the virus at a pet wholesaler from rodents imported from Ghana.
The government responded with a ban on selling prairie dogs or importing rodents from Africa.
Meanwhile, the West Nile virus, introduced into the United States in 1999, continued to spread westward through the year, reaching everywhere but Washington, Oregon, Alaska and Hawaii and causing an estimated 100,000 illnesses in 2003.
As usual, many of the biggest medical stories of the year involved progress in heart disease. Perhaps the most talked-about development was the surprisingly successful testing of an experimental treatment that actually reverses heart disease.
Based on a slightly different form of HDL cholesterol found in one village in northern Italy, the treatment, called APO A-I Milano, rolled back artery clogging by 3 percent after just five weekly injections. Although the figure sounds small, nothing before has even come close to that in such a short time.
"The benefits were very dramatic, especially because of the short time frame," said Dr. Robert Rosenson, director of preventive cardiology at Northwestern University. "It opens up the possibility of a new horizon for treatment of high-risk individuals."
Among other important heart news of the year:
The first drug-coated stent - Johnson & Johnson's Cypher - proved to be an immediate hit after its approval because of promise that it will greatly reduce the failure rate of angioplasties. Early concerns about blood clots were later discounted by the Food and Drug Administration.
Studies showed that a new blood thinner called Exanta appears to be the first alternative to warfarin, also known as Coumadin, the standard treatment for blood clots for 50 years.
Body cooling was recommended by the American Heart Association as a routine treatment for comatose victims of cardiac arrest to help prevent brain damage.
Among the biggest cancer stories of the year was an advance in breast cancer. Women whose tumors are fueled by the hormone estrogen typically take the drug tamoxifen to prevent recurrence. A new study found that another estrogen blocker, called Femara, cuts their risk nearly in half if taken by women after they finish their tamoxifen treatment.
Among other major cancer stories:
Genentech's Avastin was the first drug to show that blocking tumors' blood supply can help patients live longer, even though the benefits were modest in victims of colon cancer.
Erbitux, the ImClone drug that ensnared Martha Stewart in an insider trading scandal, was shown to shrink tumors in colon cancer patients. Swiss regulators said they would approve its sale.
An experimental vaccine showed early hints of promise against breast cancer. Another in testing is designed to prevent cervical cancer.
Proscar, a drug widely used to shrink enlarged prostates, was shown to reduce the risk of prostate cancer by one-quarter. It is the first treatment proven to ward off this common killer.
Other medical landmarks of the year included:
Congress passed the first federal prescription drug benefit that would begin providing coverage for Medicare patients in 2006.
Bad news continued to pile up against hormone replacement therapy. Already shown to slightly increase heart disease rather than prevent it, the pills do not improve women's mental sharpness, as many assumed, and may even raise the risk of Alzheimer's disease, new research showed.
Several small studies confirm what millions of dieters already believe: Low-carbohydrate fare, such as the Atkins plan, can help people lose weight, at least in the short run, and does not seem to be bad for the heart.
Scientists developed the first blood test that reveals whether people with neurological problems, such as tingling or blurred vision, will soon develop multiple sclerosis. An experimental drug called Antegren was also shown to cut the number of relapses from the disease in half.
The FDA approved Namenda, the first treatment found effective for late stages of Alzheimer's disease.
A severe outbreak of hepatitis A that caused three deaths and sickened hundreds was traced back to contaminated green onions, possibly from Mexico - raising questions about the safety of a global food supply.