An estimated 3 million intravenous (IV) drug users may be HIV positive worldwide, Reuters reports.

A new study published on September 24 examined drug use in 148 countries, revealing that HIV infection among users was higher than 40 percent in nine of them: Estonia, Ukraine, Myanmar (Burma), Indonesia, Thailand, Nepal, Argentina, Brazil and Kenya.

“Injecting drug use occurs in most countries, and HIV infection is prevalent among many populations of injecting drug users, representing a major challenge to global health,” wrote Bradley Mathers of the National Drug and Alcohol Research Centre in Australia and his colleagues.

The study showed that patterns of drug use and HIV infection vary from country to country. Reuters reports that 0.4 percent of people in Britain ages 15 to 64 used injection drugs, with 2.3 percent of them estimated to be HIV positive. However, in Spain, where only 0.31 percent of the population used injection drugs, nearly 40 percent of them are estimated to be HIV positive.