Clinical and diagnostic parameters of the reported case. A 54-year-old Caucasian presented with "varicella-like" skin rash and fever (day 0). Serological testing was negative for VZV-IgG (black circle) and VZV-IgM. A second blood sample was taken at day 2 p.r.o.. Serological testing for VZV-specific IgG (black circle) and IgM antibodies exhibited negative results. Abundant numbers of VZV-specific (CD4+/IFNγ+) T-cells could be detected within this second sample. Detected VZV-specific T-cell frequencies yielded 1% (100 in 10000 CD4+ T cells) when VZV lysate (Lysate) was used for stimulation (black bar), and 0.73% when utilizing recombinant glycoprotein E (rec.gE) (striped bar). Primary varicella could be diagnosed by virus isolation from vesicular fluid (v.f.) and by quantitative PCR for VZV-DNA out of v.f. or plasma (pl.) with Ct 16 and Ct 36, respectively. A third blood sample taken at day 6 p.r.o. demonstrated seroconversion with VZV-IgG titers of 2.2 IU/l (black circle) and VZV-IgM titers of 1:160. VZV-specific T-cells frequencies decreased to 0.19% when stimulating with Lysate and 0.17% when stimulating with rec.gE. Quantitative PCR for VZV-DNA out of plasma revealed Ct 39. A final blood sample taken at day 15 p.r.o. revealed VZV-IgG titers (black circle) of 2.4 IU/l and VZV-IgM titers of 1:160. VZV-specific T-cell frequencies further decreased to 0.063% when stimulating with Lysate, and 0.065% when stimulating with rec.gE. Abbreviations: not assayed (n/a), post rash onset (p.r.o.), vesicular fluid (v.f.), plasma (pl.), cycle threshold numbers (Ct), international units per liter as assayed by Siemens Enzygnost Anti-VZV/IgG (IU/l).