Sharing a hospital room with another person raises the risk of getting a hospital-acquired infection, Ontario scientists say.

People in semi private or ward rooms in hospitals are at increased risk of acquiring methicillin-resistant Staphyloccus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) and Clostridium difficile (C. difficile) — three superbugs that can be lethal in people who have compromised immune systems.

In Canada, according to the study, hospital-acquired infections kill between 8,000 and 12,000 people annually.

The greater the number of exposures to hospital roommates, the greater risk of infection with MRSA, VRE and C. difficile, the research shows. The increase in risk of infection was 10 per cent for MRSA, 11 per cent for VRE and 11 per cent for C. difficile.

Exposure to these bacteria was determined through an analysis of how many roommates patients were exposed to on a daily basis and the number of new people that a patient roomed with throughout their stay.

Conducted by researchers at Queen's University in Kingston, Ont., the study tracked patients between April 1, 2001, and March 31, 2006.

During this period, the Ontario hospital admitted 17,200 patients annually into 451 in-patient beds. These patients were swabbed for the presence of the bacteria and the incubation times (four days for MRSA and VRE and two days for C. difficile) were factored in.

The hospital has 107 private beds, each in its own room, 166 double-occupancy beds in 83 rooms, 18 triple-occupancy beds in six rooms and 76 quadruple-occupancy beds in 19 rooms.

"If you're in a two, three or four-bedded room, each time you get a new roommate your risk of acquiring these serious infections increases by 10 per cent," says Dr. Dick Zoutman, professor of Community Health and Epidemiology at Queen's University, in a release. "That's a substantial risk, particularly for longer hospital stays when you can expect to have many different roommates."

"Despite other advances, multi-bedded rooms are still part of hospital design in the 21st century. Building hospitals with all private rooms is not yet the standard in Ontario or Canada — but it should be," he said.

Only patients who stayed 72 hours or longer were included in the study.

The study is published on-line in the American Journal of Infection Control.