Rectal STIs and viral load in HIV positive men on and off ART
A study by O Davies and colleagues from Guy’s and St Thomas’ looked at the impact of rectal gonorrhoea (GC) and chlamydia (CT) on HIV viral load in plasma and rectal tissue. 
The study enrolled 42 HIV positive gay men half of who were on treatment and half were still treatment naive. In each group, 7 men had a rectal STI (either GC or CT) and 14 did not. The group also looked at biomarkers of inflammation in rectal tissue.
The men were recruited during routine sexual health screening. In addition to comparisons by HIV treatment and STI status, men with an STI were their own control, pre- and post- STI treatment.
In the 21 men on ART, there were no significant differences in HIV viral load between men with or without and rectal STI, with all plasma and rectal levels at <100 copies/mL. Inflammatory markers were also not significantly different between the those with and without an STI: IL-6 (p=0.41), IFN-gamma (p=0.42), and TNF-alpha (p=0.26).
Of the 21 HIV positive men not on ART, there were also no differences in viral load (p=0.50) or cytokines for those with compared to without and STI. However, there was a non-significant drop in HIV viral load in rectal tissue in this group two weeks after GC/CT treatment (median 0.6 log copies/mL; range: 0.3 to 1.4). There was also significant change in plasma (p=0.37).
The concern that STIs could increase HIV transmission risk through higher viraemia was not found in this study and perhaps helps explain the lack of transmission in the PARTNER study when STIs were present. 
While other STIs are often believed to increase the risk of HIV transmission there are limited data for many specific questions.
This is especially important given the impact of HIV treatment on reducing HIV transmission, and the data from the PARTNER study finding no transmissions even in the presence of other STIs. 
- Davies O et al. Impact of rectal gonorrhoea and Chlamydia on HIV viral load and inflammatory markers in the rectum: potential significance for onward transmission. 21st Annual Conference of the British HIV Association (BHIVA), 21–24 April 2015, Brighton. Oral abstract O19.
- Rodger A et al. HIV transmission risk through condomless sex if HIV+ partner on suppressive ART: PARTNER Study. 21st CROI, 3-6 March 2014, Boston. Oral late breaker abstract 153LB.