Clostridium difficile, a re-emerging pathogen, is the leading cause of hospital-acquired diarrhea in North America and Europe. One of the most common hospital-acquired infections, C. difficile infection (CDI) is responsible for more than 7,000 deaths annually in the U.S. alone. Major risks for CDI are exposure to antibiotics within the preceding 2 - 3 months, advanced age, hospitalization, and long-term care facility residence.

Now, CDI has been linked to anti-depressants.

For years, several types of medications were thought to increase risk of CDI, including anti-depressants. Given that depression is the third most common medical condition worldwide, a team from the University of Michigan investigated the nature of this risk.

The team first studied Clostridium difficile infection in people with and without depression and found that people with major depression had a much 36 percent higher chance of CDI than people without depression. This finding held for various depressive disorders, nervous, and psychiatric problems.

Age and family support also influenced risk of CDI. Older, widowed Americans were 54 percent more likely than their married peers to catch the infection. Simply living alone increased the risk by 25 percent.

Next, the team looked to see if there was an association between anti-depressant medication and hospital-acquired CDI. They found that out of 12 drugs tested, only mirtazapine and fluoxetine increased risk of CDI — each one doubling the risk.

"Depression is common worldwide. We have long known that depression is associated with changes in the gastrointestinal system," explained Dr. Mary Rogers who led the study. She and her team emphasized that it is not yet known whether the increase in CDI is due to microbial changes in the gut during depression or to the medications associated with depression. Recent outbreaks of CDI have been associated with a new strain (BI/NAP1/027) of C. difficile that produces more toxin than historical strains.

"Our finding of a link between depression and Clostridium difficile should help us better identify those at risk of infection and perhaps, encourage exploration of the underlying brain-gut mechanisms involved," said Dr. Rogers.

The team recommend that people who have been prescribed these types of anti-depressants need to continue to take them unless otherwise advised by their physician.