Scientists have found certain drugs could be the reason for an unexplained link between depression and Clostridium difficile (C.diff) infection.
Although most types of antidepressant did not affect infection risk, a strong association was seen with two out of 12 drugs investigated.
Mirtazapine and fluoxetine – better known as Prozac – both doubled the likelihood of acquiring the bug.
The University of Michigan team found severely depressed people had a significantly higher risk of C.diff infection than those not suffering from depression. Their chances of being infected were raised by 36%.
Older and widowed patients were also more likely to catch the bug, as were people living alone.
Study leader Dr Mary Rogers said: "We have long known depression is associated with changes in the gastrointestinal system. Our finding of a link between depression and C.diff should help us better identify those at risk of infection."