Factors affecting stable blood plasma undetectable viral loads

The ‘Swiss statement’ highlighted that it may take up to six months following initiation of antiretroviral therapy for viral load to reach stable, undetectable levels and specified that the person with HIV must remain under regular follow-up in order to monitor viral load.

Following the publication of the ‘Swiss statement’, several studies have been published examining the length of time it takes to reach a stable, undetectable viral load; the incidence of transient variations in viral load between clinic visits; and factors associated with long-term optimal adherence.

A 2010 Danish study found that risk of transmission was especially high during the first six months of treatment, when 8% of the time was spent with a viral load above 1000 copies/ml. This reduced to 1% for the following six months. Thereafter, viral load was above 1000 copies/ml for an average of 0.6% of the follow-up period. However, amongst patients who had been taking suppressive HIV treatment for over five years, only 0.03% of the follow-up period was spent with a viral load above 1000 copies/ml.

Noting that “HIV-infected patients have, however, an increased risk of abrupt viraemia in not just the first six months but the first twelve months of episodes with undetectable viral load”, the investigators recommend “there would be a substantial gain in reducing the risk of infecting the sexual partner, if the time limit recommended by the Swiss…was extended from six months to at least twelve months.”¹

A 2009 Swiss study estimated a 99% probability that HIV would remain suppressed below 1000 copies/ml in the period between routine viral load tests. Although viral load rebounded to above 50 copies/ml on at least one occasion in 43% of patients, only 7% experienced a transient viral load above 1000 copies/ml during the 3 1/2 year study period. The probability of suppression was correlated with the reported level of adherence.²

A 2010 analysis of over 2000 patients at London's Royal Free Hospital with a median of 4.5 years and up to nine years of follow-up found that most (79%) maintained an undetectable viral load for the duration of follow-up. The majority (92%) of individuals remained adherent to their antiretroviral therapy throughout the study; the chances of remaining adherent increased by about 2% a year. The study suggests that in the context of the UK’s high quality health services, adherence is high and does not decline over time, “providing encouragement that maintenance of adherence for a lifetime may well be possible," as the investigators conclude.³