HIV-1 refers to HIV type 1. HIV can be divided into type 1 and type 2, which differ in distribution, infectivity, and pathogenicity. Type 1 HIV is distributed worldwide and is slightly more infectious and pathogenic than type 2. Type 2 HIV is mainly distributed in western Africa, with a small amount of distribution in Western Europe and North America. Type 2 HIV is less infectious and pathogenic than type 1. Therefore, the majority of HIV found in China is type 1, and it is unlikely that type 2 is present. Clinical testing is done primarily by testing the blood for HIV antibodies. Most reagents are able to detect both type 1 and type 2, so either type of HIV infection can be detected.