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Tibotec-Virco NV of Belgium has presented results of a study showing that its Virco resistance tests can predict clinical response to HIV treatment for up to two years. Carried out on 681 HIV-positive patients at the Chelsea and Westminster Hospital HIV Clinic of London, the study entailed the use of Virco’s proprietary VirtualPhenotype and Antivirogram resistance tests to estimate the number of drugs to which each patient's virus was still susceptible over a 96-week period.
The viral load and CD4 cell counts were then compared for patients receiving none, one, two, three, or four active drugs. The two tests were found to be equal and significant predictors of outcomes over 96 weeks. Patients receiving three or four active drugs experienced significantly greater reductions in viral load and increases in CD4 cell count during the period of the study, and a higher proportion of these patients saw their viral loads fall to undetectable levels.
The Virco VirtualPhenotype test combines both phenotyping and genotyping. It reads the patient’s genetic code and detects all resistant mutations. The data are fed into Virco’s computer system, which searches a database of some 100,000 genotypes and phenotypes for virus samples with the same mutation patterns. The system retrieves the corresponding phenotypes for the mutations found in the patient (typically thousands for each drug) and calculates the average resistance score for each drug. It thus produces a quantitative estimate of the patient’s resistance to every available drug.