Estimating the risk of HIV transmission from homosexual men receiving treatment to their HIV-uninfected partners

Abstract

Objective: To determine how the risk of HIV transmission from homosexual men receiving antiretroviral treatment is related to patterns of patient monitoring and condom use.

Methods: A stochastic mathematical simulation model was developed of cohorts of men in the Netherlands who have sex with men (MSM), defining the parameters of the model using observational cohort data. The model incorporates viral load trends during first-line treatment, patient monitoring and different scenarios for the way in which condom use may depend on recent viral load measurements. The model does not include the effect of sexually transmitted infections on HIV transmission.

Results: For MSM receiving treatment, the risk of transmitting HIV to their long-term partner is 22% (uncertainty interval: 9-37%) if condoms are never used. With incomplete use (in 30% of sex acts) the risk is reduced slightly, to 17% (7-29%). However, the risk is as low as 3% (0.2-8%) when men receiving treatment use condoms only 6 months beyond their last undetectable viral load measurement. The risk is further reduced when 3 months is the time period beyond which condoms are used.

Conclusions: When condom use by HIV-infected men receiving combination treatment with antiretroviral agents is based on their last viral load measurement, the transmission risk is much lower than with incomplete condom use. The key message for patients is that although always using condoms during treatment is the best way to protect partners from the risk of HIV transmission, when such use cannot be achieved, the second best strategy is to use condoms whenever the last undetectable viral load was measured more than 3 months ago.

Figure 1

Schematic representation of the three assumed trajectories of (log) viral load after treatment initiation: (i) suppression achieved and adherence good (dotted line); (ii) suppression achieved but adherence poor (solid line); and (iii) suppression not achieved (dashed line). The circles indicate when the regimen was changed. Parameter values are presented in table 1 and details are provided in the online supplementary appendix.

Figure 2

Probability of transmission to partner during first-line treatment, if condoms are never used; condoms are used 30% of the time; (iii) condoms are used unless last viral load (VL) measurement in the past 6 months was undetectable; or always using condoms. Error-bars show the 95% uncertainty interval, as described in the text. It is assumed that the partnership is maintained over the entire course of first-line treatment and that viral load is related to transmission rate, as Fraser et al have described.

Figure 3

The influence of (A) monitoring frequency and (B) loss to follow-up on the probability of HIV transmission, assuming condoms are used unless last viral load measurement in the past 6 months was undetectable. It is assumed that the partnership is maintained over the entire course of first-line treatment and that viral load is related to transmission rate, as Fraser et al have described.