The STD and AIDS Prevention and Control Center, part of the China Disease Prevention and Control Center (CDC), began research Monday on an unknown virus that has shown similarities to HIV, the virus that causes AIDS.

A team of researchers will test 60 patients suspected with HIV, chosen from the national database, for the virus in two groups. Using the test samples from the nation's most trusted CDC laboratory, researchers hope to learn more about the disease and develop treatment options.

There is no current estimate of how many suspected HIV patients there are in China. The clinical AIDS authorities in Beijing, Shanghai, Guangzhou, Hangzhou and Wuhan say they receive thousands of such patients each year, and the number is growing.

Many of these patients fell ill after engaging in high-risk sexual behavior, but their test results repeatedly came back negative for HIV. Doctors think the virus may be spread by saliva and attack the immune system, but they are still unable to identify the real cause for illness. It is unclear whether the unknown virus is a new one, or if a patient's "AIDS phobia", the fear that he has AIDS, affects his doctor's judgment.