Background: The transmission of drug-resistant HIV may compromise the efficacy of subsequent ART. Resistant viral strains often have a reduced replicative capacity and may also be transmitted less efficiently. However, sexually transmitted infections (STI) have been shown to facilitate HIV acquisition. Hence STI may facilitate infection by drug-resistant viruses that might otherwise not be easily transmissible.

Methods:  Cases of primary HIV-1 infection from 2000 to 2005 were identified at a single HIV/STI treatment centre. Primary HIV-1 infection was diagnosed by one or more of the following:  negative HIV antibody test within 18 months, evolving HIV antibody response, negative antibody but positive antigen or RNA, or incident infection indicated on the Serological Testing Algorithm for Recent HIV Seroconversion (STARHS). All primary HIV-1 infection cases underwent genotypic resistance testing at the time of diagnosis and transmitted drug resistance was determined by the presence of 1 or more primary mutations (International AIDS Society 2005 criteria). We recorded demographic details and STI diagnoses (gonorrhoea, Chlamydia trachomatis, non-specific urethritis, primary syphilis, primary genital herpes simplex, and trichomoniasis) made at or within 3 months of HIV diagnosis. Statistical analysis (Fisher’s exact test) was performed using SPSS software.

Results:  We made 604 new HIV-1 diagnoses between 2000 and 2005. From those we identified 215 cases of primary HIV-1 infection (95% male, 90% men who have sex with men); 37 (17%) had transmitted drug resistance (19 nucleoside reverse transcriptase inhibitors [NRTI], 11 non-NRTI, 2 protease inhibitors [PI], and 3 had resistance to 2 or more classes). At or within 3 months of diagnosis, 160 (74%) underwent STI screening (70% of those with transmitted drug resistance, and 75% of those with wild type) with 1 or more STI diagnosed in 66 (41%) (27 gonorrhoea, 14 Chlamydia trachomatis, 35 non-specific urethritis, 3 primary syphilis, 10 herpes simplex, 1 trichomoniasis). STI were seen more frequently in the transmitted drug resistance group (62 vs 37%, p <0.05).

Conclusions:  Transmitted drug resistance is associated with the presence of STI, perhaps because STI facilitates transmission of HIV, thereby overcoming fitness barriers. Alternatively it could be explained by an association between HIV transmission and risk behavior, STI, and poor adherence to ART among individuals in sexual networks. Therefore, strategies to improve STI diagnosis and management may decrease transmitted drug resistance, as well as overall HIV transmission. The high prevalence of STI at primary HIV-1 infection, alongside the known effect of STI on genital HIV RNA, supports the need for close cooperation between HIV and STI services for newly infected individuals.