Older people living in the South tend to use more antibiotics than their counterparts living elsewhere in the United States, a new study shows.

These high rates are not tied to any differences in disease patterns, researchers found, suggesting that antibiotics may, in fact, be overprescribed in Southern states. Antibiotics overuse is linked to risk of drug resistance, and the proliferation of so-called superbugs.

According to the new study, about 21 percent of people in the South used an antibiotic each quarter of the year. By contrast, the lowest rates of antibiotic use were seen in the West, where roughly 17 percent of people used an antibiotic each quarter. Rates in the Midwest were about 19 percent.

The study, which appears online in the Sept. 24 issue of the Archives of Internal Medicine, found wide variations among antibiotic prescribing rates across geographic regions in the United States. In general, antibiotic prescription rates peak from January through March and dip from July through September, the study showed.

"There are substantial variations across the country for unexplained reasons," said study author Dr. Yuting Zhang, an assistant professor at the University of Pittsburgh. Some states, such as Oregon and Wyoming, do well in terms of keeping antibiotic prescription rates appropriate, she said, and other states could follow their lead with similar programs and policies.