Viral load one month after starting HAART predicts who will be detectable after six months treatment

Michael Carter
Published: 03 September 2004

Measuring viral load a month after starting highly-active antiretroviral therapy (HAART) can strongly predict which individuals will have a viral below 50 copies/ml after six months of treatment, according to a joint UK and German study published in the September 1st edition of the Journal of Acquired Immune Deficiency Syndromes. The early identification of patients who are not virologically responding to treatment can, the investigators suggest, allow the possible causes of poor virological suppression to be identified and addressed.

The findings underline the importance of the British HIV Association's recommendation that patients should receive a viral load test one month after starting treatment.

Investigators from the Chelsea and Westminster, and Royal Free Hospitals in London, and the JW Goethe University Hospital in Frankfurt, collected prospective data from 656 antiretroviral-naïve patients starting HAART. Viral load was measured four weeks after starting anti-HIV therapy and again at 24 weeks using ultra-sensitive assays. The investigators designed a logistic regression model to predict the odds of achieving a viral load below 50 copies/ml after 24 weeks according to the week four viral load measurement.

After 24 weeks of anti-HIV therapy, 482 patients (73%) had a viral load below 50 copies/ml. The investigators found that there was a statistically significant association between the level of viral suppression after four weeks of HAART and an undetectable viral load at week 24 (p < 0.001). Baseline viral load was also associated with viral load at week 24, with those patients whose viral load was lowest at baseline most likely to have an undetectable viral load at week 24 (p < 0.001).

In total, 84% of patients with a viral load below 1000 copies/ml at week four attained a viral load below 50 copies/ml at week 24. However, only 61% of patients who had a viral load between 1001 and 10,000 copies/ml at week four attained an undetectable viral load at week 24. The percentage fell even further for patients whose viral load was between 10,001 and 100,000 copies/ml at week four, with only 37% having a viral load below 50 copies/ml at week 24. Furthermore, only 24% of individuals whose viral load was above 100,001 copies/ml at week four had an undetectable viral load by week 24.

Using a logistic regression model, the investigators calculated that the odds of attaining virological suppression at week 24 was 65% lower for every one-log10 increase in viral load at week four.

“We found a strong association between viral load measured after four weeks of HAART and the achievement of virologic suppression at week 24,” write the investigators. They add, “it appears that individuals with a viral load of above 1,000 copies/ml at week four generally do not have a sufficiently rapid virologic response to therapy.”

“Our study shows that early measurements of viral load enable early predictions of virologic response to HAART. Reasons for negative response may include adherence, tolerability, drug levels, and drug resistance. Early predictions should enable these potential causes to be investigated and, if necessary, addressed” conclude the investigators.


Smith CJ et al Use of viral load measured after 4 weeks of highly active antiretroviral therapy to predict virologic outcome at 24 weeks for HIV-1-positive individuals. J Acquir Immune Defic Syndr 37: 1155-1159, 2004.

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