Clostridium difficile infections are the most common cause of diarrhea in hospitals, resulting in about 27,000 deaths every year in the United States. Antibiotic use is a risk factor for the infection and researchers have found that using the same bed as one who was given antibiotics during their hospital stay leads to increased susceptibility to C. difficile.

For a study published in JAMA Internal Medicine, Daniel Freedberg and colleagues observed four hospitals from the same health care system operating in the New York City metropolitan area, assessing patients admitted between 2010 and 2015. These patients had to spend 48 hours in their hospital bed after admission, with the one prior to them spending a minimum of 24 hours in the bed and leaving less than seven days before the new patient is admitted.

As the researchers were looking for C. difficile incident cases, they excluded patients who have acquired the infection before, as well as those who tested positive within their first 48 hours of being admitted. To determine if the prior patient received antibiotics, the researchers used information provided by a computerized clinician order entry system.

The study worked with 100,615 patient pairs and identified 576 where the subsequent patient developed an infection between two and 14 days of being in a hospital bed.

It also reported a median time of 6.4 days from the point a subsequent patient was admitted to the moment a C. difficile infection developed, and noted that subsequent patients were likelier to develop infections when they possess traditional C. difficile risk factors, like antibiotic use, lower albumin levels, higher creatinine levels and old age.

The cumulative risk for C. difficile infections in subsequent patients was pegged at 0.72 percent if the prior bed occupant was given antibiotics during their stay. This number drops to 0.43 percent, on the other hand, when the prior bed occupant was not given antibiotics.

"The increase in risk was small but is of potential importance given the frequency of use of antibiotics in the hospital," said the researchers.

When the researchers instead assessed for patient pairs where the prior bed occupant had a C. difficile infection recently, they found that the association between infection risk and antibiotic use still exists.

According to the researchers, antibiotics may support C. difficile proliferation in infected patients and help in increasing bacterial spores shed, which promotes the spread of the infection. Additionally, antibiotic use may interfere with healthy gut bacteria that can offer protection against C. difficile.

To better understand the underlying mechanisms of herd effects in antibiotics, Freedberg and colleagues suggest further research.

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