however, the pattern of transmission varies significantly among countries.
Blood-borne transmission can be through needle-sharing during intravenous drug use, needle stick injury, transfusion of contaminated blood or blood product, or medical injections with unsterilized equipment.
The risk from sharing a needle during drug injection is between 0.63 and 2.4% per act, with an average of 0.8%.
The risk of acquiring HIV from a needle stick from an HIV-infected person is estimated as 0.3% (about 1 in 333) per act and the risk following mucous membrane exposure to infected blood as 0.09% (about 1 in 1000) per act.
As the infection progresses, it interferes more with the immune system, increasing the risk of common infections like tuberculosis, as well as other opportunistic infections, and tumors that rarely affect people who have working immune systems.
Due to their nonspecific character, these symptoms are not often recognized as signs of HIV infection.