In this photo taken on Oct. 10, 2009, Pham Huu Khoi, who is in the advanced stages of AIDS, lays in his bed at the Mai Hoa Center for HIV and AIDS patients in the village of An Nhon Tay, 60 kilometers, (37 miles) northwest of Ho Chi Minh City, Vietnam.

LONDON – People infected with the virus that causes AIDS should start treatment earlier than currently recommended, the World Health Organization said Monday.

The U.N. agency issued new guidance advising doctors to start giving patients AIDS drugs a year or two earlier than usual. The advice could double the number of people worldwide who qualify for treatment, adding an extra 3 to 5 million patients to the 5 million already awaiting AIDS drugs.

WHO's previous HIV treatment advice was published in 2006. Since then, several studies have shown people with HIV who start drugs earlier than recommended have a better chance of surviving.

WHO now advises doctors to start HIV patients on drugs when their level of CD4 cells — a measure of the immune system — is about 350. Previously they said doctors should wait until patients' levels hovered around 200. In most Western countries, doctors start treating HIV patients when their CD4 count is about 500.

David Ross, an AIDS expert at the London School of Hygiene and Tropical Medicine, said there is compelling evidence HIV patients should start treatment sooner. People with HIV who aren't on AIDS drugs are more likely to catch a potentially fatal disease like tuberculosis or develop other complications when they do start the drugs, Ross said.

WHO's new recommendations also advise pregnant women with HIV to take the drugs earlier and while breast-feeding. The agency also said countries should phase out the use of the commonly used AIDS drug stavudine because of its toxic side effects. If countries with large outbreaks adopt the guidance, many more people could live longer, healthier lives, said Hiroki Nakatani, a top WHO official in a statement.

Still, WHO's advice raises questions about how countries and donor agencies will pay for the lifelong AIDS treatment. About 4 million people worldwide are receiving AIDS drugs, but another 5 million are still waiting in line. With its new recommendations, WHO guessed that another 3 to 5 million people now qualify for the drugs.

It may also be difficult to convince HIV patients to start the drugs sooner, when some may not have any AIDS symptoms. Putting more patients on the treatment for a longer period of time could also encourage drug resistance.

Ross said many AIDS programs in Africa are already struggling. He added there were anecdotal reports of clinics turning away new patients eligible for treatment because they didn't have enough drugs to treat them.

Some experts said the new WHO guidance could add billions to the cost of global AIDS programs. "WHO may be biting off more than they can chew," said Philip Stevens, a director at International Policy Network, a London-based think tank. "I'm not sure how this will be possible to achieve, other than by cutting lots of corners," he said.