Efforts needed to improve diagnosis of primary HIV infection to control spread, say UK researchers

Primary HIV infection may be associated with an increased risk of onward sexual transmission of HIV, according to a UK study published in the January 3^rd edition of AIDS. The investigators believe that their study provides evidence for the active management of primary HIV infection and the refocusing of HIV prevention efforts to identify and treat individuals with primary HIV infection.

The high viral load seen in individuals with primary HIV infection is though to be a major driving force behind the continued spread of HIV. It has been calculated that men with primary HIV infection viral load would infect between 7 – 24% of their female sexual partners with whom they have sex, and between 25 – 47% of men with whom they have unprotected anal sex.

In order to obtain a better understanding of the role of primary HIV infection in the sexual transmission of HIV, investigators in the UK sequenced the pol gene in individuals with primary HIV infection and obtained epidemiological data regarding sexual behaviour, clinical characteristics, and sexually transmitted infections.

A total of 103 individuals were recruited to the study between 1999 and 2003. Primary HIV infection was identified by checking medical records to see if a patient had had a negative HIV test result in the previous 18 months, or by using the seriological testing algorithm for recent HIV seroconversion (STARHS). Case notes were used to obtain data on CD4 cell count, viral load, sexually transmitted infections at the time of HIV infection, and sexual history.

The HIV pol gene was sequenced using plasma obtained at the HIV diagnosis. These sequences were used for phylogenetic analysis which has previously been shown to be able to reconstruct transmission events and clusters.

In total 99 of the 103 individuals with primary HIV infection were men, and 90 (90.9%) were gay or bisexual men. The median age was 36 years, median CD4 cell count was 526 copies/mm³, and median viral load was 100,000 copies/ml.

Resistant HIV was present in 13 gay or bisexual men (13% 0f study population), and 34 patients (35%) also had a sexually transmitted infection at the time of their HIV diagnosis.

Of the gay and bisexual men included in the study, 61 (68%) said that they had had unprotected anal sex in the three months before their HIV diagnosis.

Viruses from 35 of the 103 individuals (34%) appeared in 15 transmission clusters, including one cluster of five individuals, two of three individuals, and twelve of two. All the individuals in the clusters were men and 32 (97%) said they were gay or bisexual.

For individuals in eleven of the 15 clusters, the diagnoses of primary HIV infection were made within twelve months, supporting the theory that transmission was occurring during primary infection.

Individuals in transmission clusters had higher CD4 cell counts (p = 0.05), were younger (p = 0.05), reported a higher number of sexual partners in the three months before their HIV diagnosis (p = 0.006), and were more likely to have had unprotected anal sex in the previous three months (p = 0.05). There also a non-significant trend for individuals in clusters to have had a sexually transmitted infection at the time of their HIV diagnosis.

The investigators conclude, “the high rates of clustering observed within out study support the assertion that primary HIV infection may be associated with an increased risk of onward transmission.”

The investigators add that their data “provide further evidence that the active management of primary HIV infection will reduce HIV transmission…efforts should be re-focused on improving rates of diagnosis of individuals during primary HIV.”