A single doctor, nurse or technician with dirty hands can undo all the good work of an entire hospital staff trained to carefully wash their hands to prevent the spread of infection, French researchers reported on Monday.

This may be especially likely to happen just at the worst time -- when a hospital is overwhelmed with a disaster or a pandemic of infectious diseases and staff are reassigned to cope, the team at France's National Institute of Health and Medical Research or INSERM said.

Their mathematical model may explain some real-world outbreaks, they added in the Proceedings of the National Academy of Sciences.

Patients often get infected in hospitals with a variety of germs, include methicillin-resistant Staphylococcus aureus or MRSA superbugs. Staff who fail to properly wash their hands are often to blame for these so-called nosocomial infections.

These infections cost billions of dollars to treat and tens of thousands of patients die from them every year.

Laura Temime and colleagues at INSERM used a mathematical model of a hypothetical intensive care unit to try to calculate how this might happen.

One so-called superspreader who failed to wash his or her hands, and who traveled about the hospital treating many patients, could greatly raise the nosocomial infection rate, they calculated.

In fact a single traveling radiologist, physical therapist or other worker who failed to properly wash his or her hands after each patient visit could create a rate of infection equivalent to 23 percent of all the other staffers failing to wash their hands, Temime's team calculated.

Infection rates increased by up to three times more when a staffer moving around the hospital failed to wash his or her hands compared with a nurse, for instance, assigned to one ward.

Our findings may explain several reports of outbreaks that were traced back to peripatetic healthcare workers, they wrote.

Medicine