Main causes of virologic surveillance failures. The proportion of main causes of surveillance failures in PET (A) and LET (B) cohorts. Description of categories: no surveillance: PCR monitoring was not continued or the frequency was not as recommended; on treatment: CMV disease occurred despite antiviral treatment lasting >7 days; Ag based: patients monitored with pp65 antigenemia testing after day 100 instead of PCR testing; breakthrough: CMV diseases with undetectable viremia with adequate monitoring; threshold: detectable viremia below recommended threshold for preemptive treatment before CMV disease diagnosis, resulting in delay in antiviral treatment; positive treatment for viremia <7 days: treatment threshold was reached only within 7 days before disease onset; and no data: no information regarding PCR surveillance or start of antiviral treatment. Ag, antigen.