Like influenza, the virus could spread through airborne particles, but it was far more deadly when it infected someone. According to the WHO, 8,096 people were infected worldwide. 774 people died. The virus receded by the end of 2003.
"SARS-like infections, I think, epitomize the emerging infectious diseases," said Schaffner. As for whether the strain could re-emerge, he said, "My crystal ball is pretty cloudy about that... Trying to anticipate whether it would come back or not would be very, very difficult."
MRSA is the best-known of a number of bacteria that resist many of the antibiotics used to treat them. The emergence of MRSA and other bacteria has been blamed on a combination of heavy use of antibiotics and a lack of incentives for drug companies, leaving these bacteria, as Schaffner calls it, "a real, very vital threat"
Schaffner said the existence of these bacteria puts responsibility on both food producers and people who would use antibiotics to be more prudent. But he also said the problem could be compounded by the fact that there is currently little financial incentive for drug companies to devise new antibiotics that could fight the threat.
"Clearly, pharma sees the development of new antibiotics to help us treat these drug-resistant infections as high-risk and low-profit," said Schaffner. "I can think of no new product in any line of industry that, once it's released, the experts in that area say, 'Don't use it,' and that's the circumstance when any new antibiotic is created."
MRSA is not untreatable, but when using the stronger antibiotics for it, "You get yourself into a very restricted corner," Schaffner said. "You get patients to whom these drugs are incredibly toxic or you may need to keep patients in the hospital rather than send them home."
At the start of the decade, millions of women were using hormone replacement therapy to relieve unpleasant symptoms of menopause. It was also used prevent osteoporosis and bone fractures, and heart disease as well.
But as early as 2000, some doctors were recommending against the treatment because of a study in the Journal of the American Medical Association suggesting that it increased the risk of breast cancer.
That alarm greatly increased in 2002 when researchers cut short the Women's Health Initiative study of the treatment, citing concerns over heart problems and strokes in women in the study who received HRT.
Some researchers supported the decision to stop the study, leading many women to stop their HRT, but others felt that it discouraged women who should continue the treatments. Meanwhile, studies have come out with contradictory findings, further confusing women who were unsure what to do. Controversy over HRT continued in 2008, when the International Menopause Society released new guidelines saying that HRT was effective for post-menopausal symptoms and should be considered by women and their physicians.
Following the release of the new guidelines, ABC News contributor Dr. Marie Savard wrote a column for this site in which she tried to clear up some of the confusion.