HIV Transmission Risk
Different factors can increase or decrease transmission risk. For example, taking antiretroviral therapy (i.e., medicines for HIV infection) can reduce the risk of an HIV-infected person transmitting the infection to another by as much as 96%1. Consistent use of condoms reduces the risk of getting or transmitting HIV by about 80%2. Conversely, having a sexually transmitted infection or a high level of HIV virus in the blood (which happens in early and late-stage infection) may increase transmission risk.
The Centers for Disease Control and Prevention (CDC) is reviewing the most recent science and constructing mathematical models to update transmission risk.
Estimated Per-Act Probability of Acquiring HIV from an Infected Source, by Exposure Acta
Type of Exposure | Risk per 10,000 Exposures |
---|---|
Parenteral | |
Blood Transfusion | 9,000b |
Needle-sharing during injection drug use | 67c |
Percutaneous (needle-stick) | 30d |
Sexual | |
Receptive anal intercourse | 50e, f |
Receptive penile-vaginal intercourse | 10e, f, g |
Insertive anal intercourse | 6.5e, f |
Insertive penile-vaginal intercourse | 5e, f |
Receptive oral intercourse | lowe, i |
Insertive oral intercourse | lowe, i |
Otherh | |
Biting | negligiblej |
Spitting | negligible |
Throwing body fluids (including semen or saliva) | negligible |
Sharing sex toys | negligible |
References
1 Cohen MS, Chen YQ, McCauley M, et al; HPTN 052 Study Team. Prevention of HIV-1 Infection with early antiretroviral therapy. N Engl J Med 2011;365(6):493-505.2 Weller SC, Davis-Beaty K. Condom effectiveness in reducing heterosexual HIV transmission (Review). The Cochrane Collaboration. Wiley and Sons, 2011.
a Factors that increase the risk of HIV transmission include sexually transmitted infections, early and late-stage HIV infection, and a high level of HIV in the blood. Factors that reduce the risk of HIV transmission include condom use, male circumcision, and use of antiretrovirals.
b Donegan E, Stuart M, Niland JC, et al. Infection with human immunodeficiency virus type 1 (HIV-1) among recipients of antibody-positive blood donations. Ann Intern Med 1990;113(10):733-739.
c Kaplan EH, Heimer R. A model-based estimate of HIV infectivity via needle sharing. J Acquir Immune Defic Syndr 1992;5(11):1116-1118.
d Bell DM. Occupational risk of human immunodeficiency virus infection in healthcare workers: an overview. Am J Med 1997;102(5B):9-15.
e Varghese B, Maher JE, Peterman TA, Branson BM, Steketee RW. Reducing the risk of sexual HIV transmission: quantifying the per-act risk for HIV on the basis of choice of partner, sex act, and condom use. Sex Transm Dis 2002;29(1):38-43.
f European Study Group on Heterosexual Transmission of HIV. Comparison of female to male and male to female transmission of HIV in 563 stable couples. BMJ 1992;304(6830):809-813.
g Leynaert B, Downs AM, de Vincenzi I; European Study Group on Heterosexual Transmission of HIV. Heterosexual transmission of HIV: variability of infectivity throughout the course of infection. Am J Epidemiol 1998;148(1):88-96.
h HIV transmission through these exposure routes is technically possible but extremely unlikely and not well documented.
i HIV transmission through oral sex has been documented, but rare. Accurate estimates of risk are not available.
j Pretty LA, Anderson GS, Sweet DJ. Human bites and the risk of human immunodeficiency virus transmission. Am J Forensic Med Pathol 1999;20(3):232-239.
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