A nasty, sometimes deadly stomach bug is at least six times more common than was thought, researchers said Tuesday, based on a survey of hundreds of U.S. hospitals.

The germ, Clostridium difficile, is resistant to some antibiotics and has become a regular menace in hospitals and nursing homes. Doctors say it plays a role in hundreds of thousands of hospitalizations each year, and that number has been growing.

The latest study estimates that more than 7,100 hospital patients are infected with it on any given day. That number is between 6.5 and 20 times greater than previous estimates, according to the Association for Professionals in Infection Control and Epidemiology. Researchers from that group presented their findings Tuesday at a medical conference in Orlando.

"This study shows that C. difficile infection is an escalating issue in our nation's health care facilities," said Dr. William Jarvis, the study's lead investigator, in a prepared statement. Jarvis, formerly a scientist with the U.S. Centers for Disease Control and Prevention, is a consulting epidemiologist hired by the association.

The study suggests that about 13 per 1,000 hospital patients have the germ.

The bacteria are found in the colon and can cause diarrhea and a more serious intestinal condition known as colitis. It can be deadly, particularly to the elderly, and has been blamed in outbreaks that have killed as many as 100 people at some hospitals.

The most dangerous form is spread by spores in feces, and the spores are difficult to kill with most conventional household cleaners or antibacterial soap.

The new numbers are based on surveys of about 650 U.S. hospitals. Each hospital was asked to pick one day between May and August of this year to review every patient's medical records for documentation of the infection. A total of 1,443 infected patients were identified, and about 70 percent were older than 60.

Past studies have tried to measure the germ's incidence in different ways, making comparisons with previous estimates difficult. However, the researchers believe their latest estimate indicates the bug is far more common than previously believed.

The infection control group recommends that hospitals and nursing homes beef up cleaning efforts, such as using bleach, and that medical staff quickly isolate patients who have the infection, Jarvis said.

Last year, the same group released a report that found a dangerous, drug-resistant staph germ — methicillin-resistant Staphylococcus aureus (MRSA) — may be infecting as many as 5 percent of hospital and nursing home patients. According to that estimate, MRSA is a more common problem than Clostridium difficile, which infects about 1.3 percent.