The World Health Organization (WHO) has revised its HIV guidelines to recommend that anyone who tests positive for the virus that causes AIDS should be treated immediately.

The U.N. health agency had previously said doctors should wait to treat people with HIV until their immune systems suggested they were getting sick. In a statement Wednesday, WHO said the new recommendations are based on recent trials that have found early treatment "keeps people with HIV alive, healthier and reduces the risk of transmitting the virus."

The new guidance means that all 37 million people with HIV globally should be offered immediate treatment, a prospect that may be unrealistic in poor countries, where many patients are still unable to get medicines. Last year, only about 15 million people with HIV were being treated.

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