We found that women in Uganda and Zimbabwe established a plasma viral setpoint of 4.20 log10 HIV-1 copies/ml at 121 days and an analogous cervical viral ‘setpoint’ of 1.64 log10 HIV-1 copies/swab at 174 days from estimated date of HIV-1 infection suggesting that setpoint is achieved later in the genital compartment. Cervical viral loads were strongly correlated with plasma viral loads during the first 6 months of HIV-1 infection (p<.0001) and were significantly higher (0.7-1.1 log10 copies/ml higher) during acute infection than subsequently during the early infection period.
Our findings concerning the level and timing of the plasma viral setpoint are similar to those reported by other studies. For example, a study of 161 sex workers in Mombasa, Kenya reported a median viral setpoint of 4.46 log10
copies/ml attained at 4 months post-infection [7
]. A study of high-risk Kenyan men and women found a virus setpoint of 4.60 log10
copies/ml at 209 days post-infection [27
]. Similarly, a study among newly HIV-infected adults in the U.S. estimated the viral setpoint at 4.56 log10
copies/ml at 117 day post-infection [24
We found that subtype D infection, pregnancy and breastfeeding at the time of HIV infection were associated with a higher plasma viral setpoint while young age was associated with a decreased plasma setpoint. These findings concerning predictors of plasma viral setpoint contrast with a previous study conducted among Kenyan sex workers. In that study, DMPA use was associated with a higher viral setpoint (compared with no use of hormonal contraception) but no association was reported between older age, pregnancy, breastfeeding or subtype D infection and plasma viral setpoint [7
]. While no other analyses of predictors of viral setpoint exist, several studies have reported on predictors of HIV-1 disease progression. A Zambian study found an increased risk of disease progression (CD4 < 200 cells/mm3
or death) among women using hormonal contraception compared with women randomized to copper IUDs [28
]. Conversely, a study of postpartum Kenyan women found no differences in change in plasma viral load or CD4 counts among women initiating COCs or DMPA [29
]. Additionally, several studies suggest that older age [30
] and subtype D HIV-1 infection [31
] are associated with more rapid HIV-1 disease progression. On the other hand, most studies conclude that pregnancy, while causing transient CD4 decline, is not associated with more rapid disease progression [35
We found a dynamic in the female genital compartment similar to the plasma viral setpoint - high levels of HIV-1 genital viremia during acute infection falling to a steady-state level at about 6 months. Following the establishment of this ‘setpoint,’ genital viral loads remained constant up to 2 years post-infection. We are not aware of previous reports of a ‘setpoint’ in the genital compartment. Most previous studies have not had substantial genital viral load data from the acute and early infection periods. However, while it is well-documented that the plasma viral setpoint is predictive of subsequent disease progression [2
], the utility of a genital ‘setpoint’ as a predictor of potential infectivity to a sex partner remains to be established.
Our findings corroborate recent reports of high levels of HIV-1 genital shedding early in infection in both women and men with declining levels thereafter [5
]. Genital and plasma viral loads have also been strongly correlated in other studies (r = 0.4 to 0.7) [20
]; plasma RNA load is often the factor most strongly associated with genital RNA load in multivariable models [40
]. However the strong correlation between genital and plasma viral loads has not previously been clearly documented during early infection.
Subtype C infection, non-viral STIs, having a partner who spends nights away from home and recent unprotected sex were associated with higher cervical HIV-1 loads while time since infection was associated with decreased cervical loads. Hormonal contraceptive (COC and DMPA) use was not associated with cervical viral loads during early HIV-1 infection. Our results corroborate the findings of much previous research. For example previous studies have identified non-viral STIs [6
], recent unprotected sex and subtype C HIV-1 infection [16
] as associated with higher genital viral loads. Our findings that hormonal contraception is not associated with HIV RNA genital shedding also agrees with most (but not all) previous studies suggesting that hormonal contraception appears to be associated with shedding of HIV-infected cells (measured by HIV-1 DNA) but not cell-free virus (measured by HIV-1 RNA) in the female genital tract [8
]. However, we are unaware of previous research assessing correlates of HIV-1 genital shedding among women during early infection.
Our study has a number of important strengths. The study was prospective with samples for both plasma and cervical viral loads being collected every 12 weeks beginning before HIV infection. We measured HIV infection timing with precision by conducting HIV PCR testing on serial samples that were serologically negative. We accurately measured many variables that were potentially associated with both HIV viral setpoint and genital shedding including hormonal contraceptive use and reproductive tract infections. We also measured viral subtype from women with a variety non-B HIV-1 clades. Finally, we enrolled women seeking family planning services in two sub-Saharan countries. This allows for greater generalizability of study results than a study population drawn from a selected high-risk group (e.g. sex workers).
Our study also had limitations. We used RNAlater for storage media for cervical specimens. This resulted in lower cervical viral load levels than for specimens collected in DMSO (compared at later study visits). We only sequenced the C2-V3 region of env and thus cannot fully explore the issue of recombinant viruses. Also, some women had unprotected sex during the 3 days prior to their study visit and thus measured genital viral loads at these visits could have been a combination of the participant’s and her partner’s viral load. However, we measured unprotected sex acts in the last 3 days and adjusted for this in our model of cervical viral loads and believe that this improves the accuracy of our estimates of predictors of cervical viral loads (). Finally, we are unable to address whether a genital viral ‘setpoint’ is meaningful in terms of long-term transmission risk.
In summary, we found that cervical HIV-1 viral loads were highest during acute infection and then declined up to 6 months post-infection where they appeared to reach a setpoint. Factors associated with a higher plasma viral setpoint included older age, subtype D infection, pregnancy and breastfeeding. Factors associated with higher HIV-1 cervical loads during early infection included non-viral STIs, recent unprotected sex, subtype C infection and shorter duration since infection. Modification of these factors could result in slower disease progression (pregnancy, breastfeeding) or HIV-1 transmission risk (prevention of STI and unprotected sex). However, the prognostic value of a cervical viral setpoint on future transmission risk remains to be established.