Though anyone can get HIV through unprotected sex, multiple partners, and intravenous drug use, some racial, ethnic, and gender groups have disproportionately high infection rates. One of the most glaring disparities concerns men who have sex with men: This group makes up only about 2 percent of the U.S. population, but accounts for 67 percent of all new HIV diagnoses, according to the Centers for Disease Control and Prevention (CDC). The situation is most dire in the Southern United States, and a new study has shed some light on just how bad the epidemic has gotten there: Three out of every 10 men who have homosexual sex have been diagnosed with HIV in several Southern cities.

The report, conducted by Emory University researchers, found that 21 of the 25 metro areas with the highest levels of HIV diagnosis among these men were in the South. The cities of El Paso, Texas; Augusta, Ga.; and Baton Rouge, La., are near the top of the list with diagnosis rates of about 3 in 10. Jackson, Miss., had the highest rate in the nation at four in 10.

“For the first time, we can see not only the numbers, but the proportions,” Dr. Jonathan Mermin of the CDC told ABC News.

The team analyzed previous studies to calculate the number of men in their target population, since census information on sexually active gay and bisexual men is sketchy at best. The researchers used national counts of HIV diagnosis to determine the number of infections in different communities. Many HIV cases go undiagnosed, however, and the study only counts people who have tested positive for the virus. For this reason, the researchers are unable to determine with certainty how many HIV infections really occur in each area. They also note that it is unclear which factors are at play in causing the difference in diagnosis rates between cities.

HIV remains a largely urban disease, and large cities like New York and Los Angeles still hold the most overall cases of HIV in men who have sex with men. However, the new study offers a better understanding that the chance of being infected may be far greater in smaller, southern cities.

The CDC said this research could be important for public health officials tasked with targeting HIV prevention efforts.

Source: Rosenburg E, Grey J, Sanchez T, Sullivan P. Rates of Prevalent HIB Infection, Prevalent Diagnosis, and New Diagnoses among Men Who Have Sex with Men in U.S. States, Metropolitan Statistical Areas, and Counties 2012-2013. Journal of Medical Internet Research. 2016.