A recent study of oncology patients at a Seattle cancer treatment center is raising new questions about the threat of drug resistance after researchers found that some patients were being prescribed unnecessary antibiotic treatments, Healio reports.

Published in the journal Clinical Infectious Diseases, the study looked at antibiotic prescriptions for upper respiratory tract conditions, which are doled out to an estimated 221 per 1,000 Americans every year in the United States. Experts estimate that nearly 50% of these prescriptions are considered inappropriate—a threat so real that the Centers for Disease Control and Prevention has specifically flagged upper respiratory infections as a key target for reducing the overprescription of antibiotics.

Researchers looked at the medical records of 251 cancer patients who had recently been diagnosed with an upper respiratory illness. Of those, 32% were prescribed antibiotics, and 113 patients received viral diagnostic testing. Of those patients who were tested, upper respiratory viruses were found in 75% of patients. However, nearly one third of oncology patients were prescribed antibiotics for their illness at the center, despite the fact that antibiotics are indicated for bacterial infections—not viruses.

Such overprescription, studies have shown, has caused bacteria to become increasingly resistant to the antibiotics previously used to treat them. This poses a significant threat to public health, as some common infections have been rendered more difficult to treat. What’s more, cancer patients on chemo and radiation therapy often have weakened immune systems, compounding the risk of bacterial infection and potential harm.

The study authors conclude: “These findings highlight the need for future research to explore the role and cost effectiveness of molecular respiratory viral testing in limiting unnecessary antibiotic uses among hematology-oncology patients.”