Taking the antidepressant Prozac increases the risk of infection by a hospital bug, a study has shown.

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."