Antibiotic Misuse in Covid Tied to Resistance

Taking azithromycin for as little as one day triggers antibiotic resistance in the respiratory tract, study finds.

Mar. 17, 2026 at 7:54am by Ben Kaplan

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A study by researchers at UC San Francisco found that taking the antibiotic azithromycin, even for just one day, can trigger antibiotic resistance in the respiratory tract of hospitalized COVID-19 patients. The study followed 1,164 COVID-19 patients at over 20 U.S. hospitals and compared those given azithromycin to those given no antibiotics or other antibiotics. The results showed azithromycin changed the mix of microbes in the upper airway, decreasing some normally harmless bacteria while increasing potentially harmful bacteria, with these changes persisting for over a week.

Why it matters

Azithromycin is one of the most widely used antibiotics in the world, but it does not work against viruses like COVID-19. Early in the pandemic, azithromycin was widely prescribed to COVID-19 patients despite a lack of evidence of its effectiveness, contributing to the growing problem of antibiotic resistance. This study provides important data on the immediate impact of unnecessary antibiotic use, highlighting the need to be judicious with antibiotics, especially during viral outbreaks.

The details

The study, published in Nature Microbiology, found that taking azithromycin for as little as one day triggered the activation of antibiotic resistance genes in the respiratory tract of hospitalized COVID-19 patients. Researchers compared patients given azithromycin to those given no antibiotics or other antibiotics, and found azithromycin changed the mix of microbes in the upper airway, decreasing some normally harmless bacteria while increasing potentially harmful bacteria. These changes persisted for more than a week.

  • The study followed 1,164 COVID-19 patients hospitalized at over 20 U.S. hospitals between May 2020 and March 2021, before COVID vaccines were widely available.

The players

Chaz Langelier

MD, PhD, lead author of the study.

UC San Francisco

The university where the study was conducted.

National Institute of Allergy and Infectious Diseases (NIAID)

The NIH institute that provided partial funding for the study.

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What they’re saying

“We've known for years that antibiotics don't treat viral infections, but these results were striking. That we could see resistance genes turning on in the respiratory tract within a day tells us the consequences of unnecessary antibiotic use aren't theoretical or long-term. They're immediate, measurable, and biologically real.”

— Chaz Langelier, MD, PhD (Mirage News)

What’s next

The researchers plan to look at whether other widely used antibiotics, such as amoxicillin and ceftriaxone, exhibit similar effects in hospitalized COVID-19 patients.

The takeaway

This study highlights the urgent need to be judicious with antibiotic use, especially during viral outbreaks like the COVID-19 pandemic, in order to combat the growing threat of antibiotic resistance. The immediate impact of unnecessary antibiotic use on the respiratory microbiome underscores the importance of restricting antibiotics to only those cases where they are truly warranted.