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

That guidance fits with what is already recommended in many developed nations, including the United States.

The U.N. health agency had previously said doctors should wait to treat some people with HIV until their immune systems suggested they were getting sick. But 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.

WHO says the sickest patients should be prioritized and that people who are at high risk of being infected should also be offered preventive therapy.

While other experts commended the new guidelines, they warned that fulfilling them would require a substantial cash injection and an overhaul of current strategies.

"To work as a tool to control the epidemic, (these guidelines) will require drastic changes and increased investment," said Dr. Tom Ellman, director of the Southern Africa Medical Unit for Doctors Without Borders. "Nobody's going to end AIDS with business as usual."

He said HIV treatment had to move out of the clinics into the communities where patients live.

WHO and the U.N. AIDS agency estimated that implementing the new guidelines could avert 21 million AIDS deaths and prevent 28 million new infections by 2030.