Adverse health events such as Clostridium difficile (C diff) infection can follow antibiotic prescriptions for acute upper respiratory infections, according to a large new study. More than 60% of patients received antibiotics for acute upper respiratory infections, and many of these cases lead to serious side effects.

Investigators examined insurance claims data on 51 million U.S. patient experiences over 15 years. They tracked adverse events that followed antibiotic prescriptions for acute upper respiratory infections, looking specifically for candidiasis, diarrhea, C diff infection or a mix of those outcomes.

Patient outcomes were compared with those who did not receive antibiotics for their upper respiratory infections.

“The scale of the problem is enormous,” said Harris Carmichael, MD, the study’s principal investigator and a hospitalist at Intermountain Health in Salt Lake City, UT.

The relative likelihood of an adverse event rose 30% for patients receiving antibiotics, they found. Not only were some of the most dangerous antibiotics commonly used, despite lack of indication, but 1 in 300 with those prescriptions developed side effects that required a doctor’s follow-up or hospitalization. 

Antibiotic use resulted in 30,133 cases of C diff infection, an additional 5.7 cases per 100,000 outpatient prescriptions. Adverse health events associated with antibiotic usage overall occurred in 1 out of every 1,150 prescriptions. And female patients were more likely to be diagnosed with any of the adverse outcomes tracked in the study, the researchers noted.

“These findings underscore that inappropriately giving patients antibiotics is causing real and widespread harm,” Carmichael said in a statement. “Having these kinds of side effects for one in a few hundred, or even a thousand, patients may not seem like a lot, but when you look at this problem on a population health level, we’re talking about hundreds of thousands of adverse events severe enough that these patients needed additional care from a doctor.”

Find full findings, published in the Journal of Internal Medicine, here.