CHICAGO (Reuters) - Drug-resistant bacteria are infecting more people in community settings such as prisons and public housing, and not just in hospitals where such "superbugs" can run rampant, researchers said on Monday.

Over a five-year period, researchers at a Chicago hospital found a seven-fold increase in drug-resistant staph infections that had been contracted outside of any hospital.

They projected the rate of infection rose to 164 cases per 100,000 people in 2005, up from 24 cases per 100,000 in 2000.

The stubborn infections -- known as methicillin-resistant Staphylococcus aureus -- do not respond to standard antibiotic treatment, said the report published in the Archives of Internal Medicine.

Drug-resistant infections caught in U.S. hospitals kill 90,000 people annually and cost $4.5 billion, according to the U.S. Centers for Disease Control and Prevention. The problem has also been documented in Canada and Britain.