Deaths from the infections more than doubled from 1999 to 2007, to more than 17,000 a year from 7,000 a year, the Centers for Disease Control and Prevention reported. Of those who died, 83 percent were over age 65. Two thirds of the deaths were caused by a bacterium, Clostridium difficile, which people often contract in hospitals and nursing homes, particularly when they have been taking antibiotics. The bacteria have grown increasingly virulent and resistant to treatment in recent years.

But researchers were surprised to discover that the second leading cause of death from this type of illness was the norovirus. It causes a highly contagious infection, sometimes called winter vomiting illness, that can spread rapidly on cruise ships and in prisons, dormitories and hospitals. “I think there is perhaps a misperception that norovirus causes a mild illness,” said Aron Hall, an epidemiologist at the disease centers. “But this suggests a major problem that requires some attention.”

...Problems with C. difficile are not new: Health officials first began warning in 2004 that a more virulent and drug-resistant strain had emerged. It produces high amounts of two potent toxins that can wreak havoc in cells lining the intestine. But few people anticipated what gains the bacteria would make. Among hospitalized patients, cases rose to 336,000 in 2009 from 139,000 in 2000. Deaths from the infection seem to have leveled off in the past few years, but researchers say they are still far too high and should be dropping, as other hospital-related infections are. Estimates of cases occurring outside hospitals run as high as three million annually. Overall, C. difficile infections cost $1 billion a year, according to the disease centers. Two factors typically lead to the infection: taking antibiotics, which make the intestine vulnerable, followed by exposure to the bacteria or their spores in a hospital, clinic or nursing home that has not been properly disinfected. Spores can survive for weeks or maybe even months outside the body, and it takes bleach or other strong disinfectants to kill them. ...A quarter of the infections start in the hospital, and the rest occur in nursing home patients or people recently treated in doctors’ offices or clinics. Patients often carry the germs from one institution to another.

--"Gut Infections Are Growing More Lethal", NYT