Table 2.

Summary of the Definitions of Refractory Cytomegalovirus Infection and Disease and Antiviral Drug Resistance for Use in Clinical Trials

Term	Definition
Refractory CMV infection	CMV viremia that increasesa after at least 2 wk of appropriately dosed antiviral therapy
Probable refractory CMV infection	Persistent viral loadb after at least 2 wk of appropriately dosed antiviral therapy
Refractory CMV end-organ disease	Worsening in signs and symptoms or progression into end-organ disease after at least 2 wk of appropriately dosed antiviral therapy
Probable refractory CMV end-organ disease	Lack of improvement in signs and symptoms after at least 2 wk of appropriately dosed antiviral drugs
Antiviral drug resistance	Viral genetic alteration that decreases susceptibility to one or more antiviral drugsc

Abbreviation: CMV, cytomegalovirus.

^aMore than 1 log₁₀ increase in CMV DNA levels in blood or serum and determined by log₁₀ change from the peak viral load within the first week to the peak viral load at ≥2 weeks as measured in the same laboratory with the same assay.

^bCMV viral load at the same level or higher than the peak viral load within 1 week but <1 log₁₀ increase in CMV DNA titers done in the same laboratory and with the same assay.

^cKnown examples involve genes involved in antiviral drug anabolism (eg, UL97-mediated phosphorylation of ganciclovir), the antiviral drug target (eg, UL54, UL97, UL56/89/51), or compensation for antiviral inhibition of biological function (eg, UL27).