Viral load in early HIV infection predicted by that of transmitting partner

Viral load in individuals recently infected with HIV is closely related to that of the individual who transmitted the virus, US investigators report in the online edition of AIDS.

“We found a strong correlation between HIV-1 RNA levels in source and recipient partners in HIV-1 transmission pairs”, comment the investigators.

The study also provided some insights into the factors contributing to the ongoing HIV epidemic. Notably, approximately two-thirds of the source individuals who transmitted HIV had only recently been infected with the virus themselves.

Viral load in early HIV infection has been identified as an important factor in disease progression and individuals who have higher viral loads at this time have a poorer overall prognosis.

Research examining the factors that influence viral load in early infection have tended to focus on the characteristics of the host patient. However, investigators from the UCSF Options Project wished to explore the significance of viral characteristics.

They therefore sought to determine the relationship between viral load in source partners and that in the partner they infected within identified transmission pairs.

Their research involved 24 individuals with evidence of recent HIV infection.

These patients provided information about the individuals they believed had transmitted HIV to them. With consent, they were contacted by the investigators, and after agreement to participate in the study, had a number of blood tests and provided details about their HIV testing and treatment history.

A total of 23 source individuals were identified and included in the study (one individual transmitted HIV to two partners). All 47 individuals included in the study were gay men.

Phylogenetic analysis was used to confirm a relationship between the virus in the infected and source partners.

The recently infected individuals had a median CD4 cell count of 528 cells/mm³ and a median viral load of 86,332 copies/ml.

Median CD4 cell count in the source individuals was 372 cells/mm³, and their median viral load was 23,951 copies/ml.

Of note, the viral characteristics of nine of the transmitting individuals suggested that they too had only recently been infected with HIV. This finding adds to research suggesting that recently infected, and therefore usually undiagnosed individuals, are of key importance to the continuing HIV epidemic.

Four of the source patients had a history of antiretroviral therapy. One had stopped therapy after three months, and another had interrupted treatment shortly before their study visit. None had an undetectable viral load, which ranged between 6776 to 137,000 copies/ml.

Analysis showed viral load in the source and infected partners were closely correlated (p = 0.009).

The viral load of the recently infected partner increased by 0.43 log₁₀ with every one log₁₀ increase in the viral load of the transmitter.

Next the investigators conducted an analysis to see if this relationship persisted over time. They restricted this to the recipient partners who did not start antiretroviral therapy.

The investigators found a significant correlation between source and recipient viral load over 48 weeks (p = 0.042).

Adjustment for potentially confounding factors such as age, race and other viral characteristics did not affect these results.

“In summary, our observations suggests a strong influence of viral genetic factors on HIV-1 RNA levels during early infection”, conclude the investigators.

They write: “Subsequent research is needed to better identify the viral genetic characteristics associated with higher or lower HIV-1 RNA levels, and to further understand host immune responses that shape viral replication over time.”