HIV-1 Transmission, by Stage of Infection

September 2008

HIV-1 Transmission, by Stage of Infection

Hollingsworth T, et al. J Infect Dis 2008;198:687-693. [PubMed Abstract]

Purpose: To determine the risk of transmission of HIV by stage of disease to facilitate targeted public health interventions.

Methods: Transmission hazards and duration of periods of high infectivity based on viral load were determined for three stages of HIV infection: primary infection, asymptomatic infection, and AIDS. Transmission risks were determined using data from the discordant couple study in Rakai, Uganda (Wower MJ J Infect Dis 2005;191:1403).

Results: The risk of transmission was correlated with viral load. The mean rate of transmission was 10.6/100 person-years and the average viral load observed prior to the index partner death was 112,000 c/ml. The initial stage of infection, primary HIV, was associated with a very high viral load and high infectivity, but lasted only an average of 2.9 months. The period of high infectivity before death is lower in terms of risk by person-year, but is substantially greater than during primary infection simply because of the longer duration which was estimated at 10-19 months. The stage associated with the lowest risk per coital act was the asymptomatic period in the middle, but this lasted an average of 8.4 years so that the long duration of exposure made this the period of least risk by person-year, but greatest risk due to the long duration. These data are summarized in the following table:

Risk of transmission by HIV stage

Stage

RR transmission/

Person-year

Duration risk Interval

From Seroconversion

To Death

New transmission by sex behavior

(monogamy)

PrimaryAsymptomaticAIDS

2.7

0.1

0.8

0.24/10.2

8.4/10.2

0.75/10.2

0.10

0.8

0.2

Conclusion: The authors conclude that both primary and late stage HIV infection are associated with greater efficiency of transmission, but the lifetime risk is much greater for the asymptomatic stage due to the long duration.

Comment: These data do not agree with those of Pilcher et al. which suggest that primary infection accounts for up to 40% of all transmissions in the lifetime of an untreated patient with HIV infection (J Infect Dis 2004;189:1785). It is all in the math, but very important to solve due to the impact on “Treatment as Prevention” as an HIV elimination strategy since the Pilcher calculations would suggest 40% of transmissions would occur before the first HIV test.