Regarding its prevalence, R263K mutation is very rare in cART-naïve patients, in the French epidemiological transmitted drug resistance survey conducted in patients in primary infection with a prevalence of 0.9% (n = 2/233 patients) . In a study based on 92 recently diagnosed, but chronically-infected, cART-naïve patients, no R263K was detected by Sanger sequencing technology and was found in two samples in minority proportion only when using ultra-deep sequencing technology .