The Centers for Disease Control and Prevention (CDC) has compiled a list of 220 counties across the nation where injection drug users are especially vulnerable to outbreaks of HIV and hepatitis C, reports The Wall Street Journal.

The findings are based on factors such as overdose deaths, unemployment rates and the sale of prescription painkillers. More than half of the counties—56 percent—are located in Kentucky, Tennessee and West Virginia, with clusters in Arizona, Utah, Missouri, Michigan, Maine, Montana, California and other states.

The CDC is hoping to avoid a repeat of last year’s outbreak of HIV and hepatitis C virus (HCV) in Austin, Indiana, a rural town where almost 200 people are infected because of drug use and where the projected lifetime cost of treating them approaches $100 million.

“Our main goal was to prevent this from happening again, and this is one way we think we can help jurisdictions,” John Brooks, senior medical adviser for the CDC’s Division of HIV/AIDS Prevention and lead author of the analysis, told The Wall Street Journal. He added that this “doesn’t mean these are the only places that have a problem.”

To work with the counties, the CDC released its findings to the states. It is urging them to increase their testing for HIV and hep C and to develop plans for dealing with outbreaks.

The CDC’s full report will be published in the Journal of Acquired Immune Deficiency Syndromes.