At the end of a hospital shift, a doctor's white lab coat that hasn't been washed recently doesn't harbour any more bacteria than a short-sleeved uniform that began the day freshly laundered, a new study suggests.

Researchers at the University of Colorado decided to look into the matter because the United Kingdom recently brought in guidelines banning doctors' white coats and long-sleeved garments, aiming to reduce the transmission of infectious pathogens.

Dr. Marisha Burden, interim chief of hospital medicine at Denver Health, says white coats offer convenience and some protection to doctors, and surveys have indicated that patients mostly prefer to see their doctors in a white coat.

And some physicians-in-training who took part in her study — the ones randomly assigned to wear the clean short-sleeved outfits — balked a bit, wondering how they'd be able to function without the big pockets.

"I'm about 4 1/2 years out of residency and I totally understand that feeling," she said in an interview. "I totally depend on my pockets for different things as well."

Fifty doctors in internal medicine units were asked to start the trial in a standard, freshly washed uniform, while 50 other physicians were assigned to wear their usual lab coats and weren't told they were in the study until it began — so that they were following their usual routine and wouldn't launder their white coat first or change to another coat.

Of those assigned to their own white coats, 15 reported washing it weekly, while 21 washed it every two weeks, eight said every four weeks, and five doctors admitted to laundering their coat every eight weeks. One doctor said "rarely."

At the end of the day, researchers compared the degree of bacterial and methicillin-resistant Staphylococcus aureus contamination.

Colony counts on the freshly laundered uniforms were zero at the start of the day. After three hours, they rose to almost 50 per cent of those counted at eight hours.

By the end of eight hours, tests for bacteria were conducted on the sleeve cuffs, the pockets and the skin of the wrists of the doctors.

No statistically significant differences were found in bacterial or MRSA contamination between the white coats and the clothes that had been clean.

"It was not what we expected, that's for sure, because we were assuming that the white coats, because they're not washed for one thing, that they would be more contaminated with bacteria as well as resistant organisms," said Burden.

"The group who came in with a very new fresh ... uniform that morning — by the end of the eight-hour workday (there) was no difference in that group compared to the white coats that hadn't been changed, really, in weeks."

However, she said the study doesn't tell us anything about the possible transmission of bacteria from a coat sleeve, for example, to patients.

"Maybe a sleeve cuff might be more inclined to touch the patient, but it's cloth onto the patient's skin or clothing. It's really hard to say. ... When you're examining a patient, you're touching them with your hands, so I think handwashing in general is probably one of the better things that everybody can do to actually cut down on infection."

And she doesn't think that physicians should take away from this study the message that they don't need to wash their white coats.

"I think you want to have a clean white coat for the appearance of cleanliness for your patients," she said.

In Toronto, Dr. Allison McGeer, director of infection control at Mount Sinai Hospital, said she found the study's results to be "interesting and useful."

"I think there's a lot of controversy about the extent to which we should be investing resources in having clothes that are not contaminated when it's pretty clear that it's not the clothes that make that much difference," she said, adding that hand hygiene and a number of other practice issues are more important.

"I don't think this is enough evidence to say lab coats are not a problem. At the same time, honestly, I'm not that worried about lab coats. Not at the top of my list."

But she's wary about the findings on frequency of laundering.

"In some senses, I would rather this study not have come out because what this study does is it makes it look like washing a lab coat is not important, when in fact it still might be," she said.

"Lab coats get full of things, and people don't always think about washing them. It's not always that convenient and so I'm not that happy with results that suggest it doesn't matter."