Low-level viral rebound (LLVR) was identified in 704 of 2055 patients on effective antiretroviral treatment. It was followed by a value of 50 copies/ml, a ‘blip', in 490 patients, whereas two consecutive values between 51 and 500 copies/ml, a ‘bump', were observed in 155. Hazard ratios of viral failure were 2.01 for blips and 5.80 for bumps. LLVR is frequent and generally resolves spontaneously, but is associated with an increased risk of viral failure.

The occurrence of viral rebound to a moderate level (51–500 copies/ml) raises concern regarding the durability of response to antiretroviral therapy (ART) as it has been correlated with sequence evolution [1–3], with failure to reduce the number of latently infected cells [4], and with drug resistance mutations in the latent reservoir [5]. However, low-level viral rebound (LLVR) could be caused by test variability [6], polymerase chain reaction contamination, non-compliance, intercurrent infection, or vaccination [7]. When evaluating the nature of ‘blip', clinicians should be aware of the variability of the ultrasensitive amplification methods. Inter-assay and intra-assay coefficient variability of up to 35.4 and 40%, respectively, has been reported for this assay [6].