Regional and Seasonal Variation in Antibiotic Use, Pitt Research Finds

Yuting Zhang, Ph.D

Doctors treating older patients in Southern states are more likely to prescribe antibiotics than any other region in the United States, an important finding from a University of Pittsburgh study that could guide and target policy efforts to prevent antibiotic overuse.

In the first examination of antibiotic use among people age 65 and older using national Medicare Part D data from 2007 through 2009, University of Pittsburgh Graduate School of Public Health assistant professor Yuting Zhang, Ph.D., and her colleagues found substantial geographic and seasonal variation in antibiotic use. The variation persisted after adjusting for regional differences in population demographics, insurance status and clinical characteristics, such as health status measured by risk scores or an extended nursing home stay.

The findings were published today in the online issue of the Archives of Internal Medicine, a JAMA Network journal.

“Overuse of antibiotics is common and the consequences of overuse are substantial,” said Dr. Zhang, director of the Pharmaceutical Economics Research Group in Pitt Public Health’s Department of Health Policy and Management, and lead author of the study. “Not only can it lead to unnecessary spending for prescription drugs, it can also increase antimicrobial resistance.

“Unnecessary drug prescribing in the elderly can be especially dangerous because of older patients’ increased susceptibility to side effects and allergic reactions,” Dr. Zhang added.

In the South, an average of 21.4 percent of patients seen in outpatient settings filled an antibiotic prescription between 2007 and 2009, with the highest rates in Alabama and Mississippi. The rate was lowest in the West, at 17.4 percent of patients, with the lowest rates in Oregon and Wyoming. In the Midwest, 19.2 percent of patients filled an antibiotic prescription, while 18.2 percent of patients in the Northeast did.

Regional variation in antibiotic prescribing did not seem to be explained by regional differences in the prevalence of major infections. For example, compared to other regions, the South had the highest rates of non-specific upper respiratory infections, for which antibiotics typically are not recommended because these types of infections are viral.

This information could be used to create and refine programs that seek to reduce unnecessary antibiotic use, Dr. Zhang said. The low rates of antibiotic use in the West could be used as an example of an attainable goal for the higher prescribing regions.

The season also influenced antibiotic use rates, which were highest from January through March, at 20.9 percent, and lowest from July through September, at 16.9 percent. The rate was 18.5 percent from April through June, and 19.8 percent from October through December.

The Medicare population used more antibiotics, at 1.10 prescriptions per year, compared to previous findings of 0.88 prescriptions per year in children and adults younger than 65.

“Older adults often have multiple disorders or diseases, making them more susceptible to complications from untreated infections,” said Dr. Zhang. “So there is an incentive for physicians to treat older patients more aggressively with antibiotics. However, older patients might be subject to more severe adverse outcomes of antibiotic use and bacterial resistance is a societal concern. Thus, physicians should be extra careful to ensure not to prescribe unnecessary antibiotics to older patients.”

Co-authors include Cameron M. Kaplan, Ph.D., of Pitt Public Health’s Department of Health Policy and Management, and Michael A. Steinman, M.D., of the University of California San Francisco Division of Geriatrics and the San Francisco VA Medical Center.

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