Relationship of Viral Resistance Development to CD4 Monitoring Alone or With Viral Load Monitoring

Antiretroviral therapy (ART) has become widely available in resource limited settings (RLS) due to large increases in available resources through the President s Emergency Plan for AIDS Relief (PEPFAR) and the Global Fund for AIDS, Tuberculosis, and Malaria (GFATM). The number of people accessing ART in RLS doubled in 2005 alone. Whereas viral load testing is done routinely for individuals on ART in the western hemisphere, this is not the case elsewhere. The World Health Organization (WHO) has recommended only clinical and CD4 count monitoring as the standard of care in RLS during the ART scale-up. As a result, there is a growing population of individuals in Africa currently on ART whose treatment is monitored only using clinical evaluations and CD4 counts.

In addition to preserving lives and improving the quality of life of HIV infected individuals, the goal of ART is to achieve and maintain suppression of HIV replication to an undetectable level. This goal enables the treatment to remain effective in the long term since the emergence of resistant strains is limited by the low replication rate of HIV achieved under these conditions. The recovery of the immune system as determined through CD4 count monitoring is neither a very sensitive nor specific marker of virological suppression in individuals on ART. Therefore, monitoring the response to ART using just the WHO guidelines for RLS may lead to a significant delay in detecting the failure to achieve or maintain virological suppression among individuals who are failing treatment. This is in contrast to western settings where routine viral load testing leads to early detection of failure to achieve suppression.

Failure to monitor and detect unsuppressed virus increases the risk of development of resistance to ART. In particular, failure to achieve or maintain virologic suppression for prolonged periods of time may lead to the sequential development of thymidine analogue mutations (TAMs) in patients taking zidovudine (AZT) or stavudine (d4T) as part of ART regimens. The accumulation of 3 or 4 TAMs confers drug resistance across the nucleoside reverse transcriptase inhibitors (NRTI) class of antiretroviral (ARV) drugs and has implications for future ART regimens, particularly in RLS where second line ART options are limited. Stavudine and zidovudine are currently used as part of the first line regimens in Sub-Saharan Africa and other RLS areas.

We hypothesize that patients who are monitored with a combination of CD4 counts and viral load measurements routinely develop TAMs at a slower rate than do patients who are monitored with only CD4 count measurement (as per WHO guidelines in RLS). This hypothesis is based on the higher risk of delay in detection of unsuppressed virus in patients who are monitored by clinical and CD4 counts alone, which may translate into the development of drug-resistant mutations.

The study team therefore proposes to carry out a cross-sectional study in a large public HIV out-patient clinic in which patients who are routinely monitored with both CD4 count and viral load measurements are compared with patients who are routinely monitored with CD4 counts measurement only. Individuals who have detectable viral load after 36 months of ARV therapy in each of the above patient categories shall undergo a structured interview and HIV genotypic testing, particularly to look for TAMs. The presence of TAMs in each instance shall be documented.

The results of this study will highlight the magnitude of the risk of using CD4 count monitoring only in patients on ART in RLS and contribute to efforts to find cheaper technologies for virological monitoring of these individuals. The findings will also support the choice of second line drug regimens that may be proposed for use in Africa.