factors increasing the risk of HIV transmission
The probability of HIV transmission depends upon the exposure characteristics, the infectivity of the source and host susceptibility. Where individuals have multiple exposures within 72 hours a cumulative risk should be considered.
The following factors have been reported to increase the risk of HIV transmission:
- a high plasma HIV viral load (VL) in the source
- with each log10 increase in plasma HIV RNA the per-act risk of transmission in increased 2.9 fold [95% confidence interval (CI) 2.23.8]
- this may be particularly relevant during primary HIV infection
- breaches in the mucosal barrier
- such as mouth or genital ulcer disease and anal or vaginal trauma following sexual assault or first intercourse
- menstruation or other bleeding
- sexually transmitted infections
- in HIV positive individuals not on antiretroviral therapy or HIV negative individuals with genital ulcer disease
- ejaculation
- among a community cohort of men who have sex with men (MSM) the risk of HIV acquisition per episode of unprotected receptive anal intercourse with and without ejaculation was estimated to be 1.43% (95% confidence interval [CI] 0.48 -2.85) and 0.65% (95% CI 0.15 - 1.53), respectively
- non-circumcision
- circumcision has been shown to significantly reduce HIV acquisition among heterosexual men in high prevalence countries
- in 2008 a meta-analysis of observational studies in MSM suggests circumcision has little impact upon HIV acquisition. However, since then the risk of HIV acquisition per episode of unprotected insertive anal intercourse in circumcised men was estimated to be 0.11% (95% CI 0.02 -0.24) versus 0.62% (95% CI 0.07 -1.68) in uncircumcised men in a community cohort of MSM in Australia
- discordant HIV viral load in the genital tract
- in general, the genital tract viral load is undetectable when the plasma viral load is undetectable. When this is not the case the viral load in the genital tract is usually low
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