Mutations conferring ganciclovir resistance in a cohort of patients with acquired immunodeficiency syndrome and cytomegalovirus retinitis

Cytomegalovirus (CMV) retinitis is among the most common opportunistic infections in patients with acquired immunodeficiency syndrome. In a prospective study of 210 patients with CMV retinitis, 26 were identified as having either a phenotypic or a genotypic ganciclovir-resistant isolate from either blood or urine cultures. For blood culture isolates with an IC₅₀ >6.0 μm for ganciclovir, the sensitivity and specificity for detecting a UL97 mutation were 95% and 98%, respectively, whereas for an IC₅₀ >8.0 μM they were 79% and 99%, respectively. Although there were trade-offs between the 2 thresholds for blood culture isolates, for urine culture isolates an IC₅₀ >8.0 μM appeared to be better at identifying genotypic resistance. UL97 mutations identified in both the blood and urine cultures of individual patients were identical in 87.5% of cases. High-level ganciclovir resistance (IC₅₀, >30 μM) typically, but not invariably, was associated with a mutation in both the UL97 and UL54 genes.