The answer lies in the concept of post-exposure prophylaxis which involves the use of a combination of anti-retroviral drugs for a short period of time to reduce the risk of seroconversion (immunological process of conversion from HIV negative to HIV positive).
The risk of HIV spread from a single needle stick injury from an HIV infected person is approximately 0.3% and approximately 0.09% with mucous membrane exposure.
Risk after exposure to body fluid or tissue other than blood is thought to be considerably lower than with blood. It should be noted however that the more blood or body fluid is involved and the sicker the patient (source), the greater the risk of transmission.
Newly infected patient also have high viral loads and are more infectious.
Immediate steps post-exposure: Wash exposed wound or skin surface with soap and water.
For needle stick injury, allow it to bleed for a few seconds before washing, do not apply caustic agents into the wound. In case of rape, the private part can be washed with soap and water usually after evidence of seminal fluid etc has been obtained by the police. Then the victim should be taken to a doctor who will prescribe antibiotics and emergency contraceptive to prevent sexually transmitted diseases (venereal infections) and pregnancy respectively.
Post-exposure prophylaxis should generally be given when the source of the exposure is known to be or is likely to be HIV infected. In high prevalence regions, post-exposure prophylaxis may be provided even if HIV status is unknown. If available, rapid HIV tests may be used to determine HIV status of the patient (HIV positivity of the exposed person immediately post-exposure is obviously a reflection of previous infection). Do not delay starting post-exposure prophylaxis by waiting for results of standard delayed-result HIV after exposure and repeat at 3 and 6 months. Start post-exposure prophylaxis within as soon as possible, preferably within 24-48 hours of exposure even with unknown HIV status of the client. If HIV status proves negative, discontinue. Recommended post-exposure prophylaxis for low-risk exposure is zidovudine (ZDV)300mg and lamivudine (3TC)150mg, each twice daily for 4 weeks. High-risk exposures require a 3-drug regimen: one combivir tablet (300mg ZDV and 150mg lamivudine, 3TC)twice daily with Efavirenz (600mg nocte) or indinavir (IDV)800mg three times daily for 4 weeks.
Conclusion
While the search for an efficacious HIV vaccine continues, world health organization recommends that; ART should be delivered as part of a package of care involvements as well as therapeutic care, providing contrimoxazole preventive treatment, nutritional sustenance and management of opportunistic infections.