The lower limit of detection was 10 VZV DNA
copies per reaction. A hierarchical case-definition
algorithm was used to classify each suspected
case. If the PCR assay was positive for VZV, the
case was confirmed. If the PCR assay was negative
for VZV and positive for β-actin (internal
control), the case was classified as not herpes
zoster. If all three samples were negative for
both VZV and β-actin, or if lesion samples were
not available, the final diagnosis was determined
by unanimous agreement among the five members
of an ascertainment committee. The members
of this committee, who were unaware of
PCR results and study-group assignments, reviewed
all suspected cases on the basis of available
clinical information, such as rash and pain
evaluations, digital photographs, and clinical
progress notes.