Reliability of a History of Previous Varicella Infection in Adults

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Abstract
Context. —Apparent second episodes of varicella are reported in immunocompetent hosts, but laboratory confirmation of prior immune status has rarely been possible. Objective. —To evaluate adult patients with varicella who claimed to have had previous varicella to determine whether they had true second episodes or primary cases with inaccurate clinical histories. Design. —Adult subjects with varicella who enrolled in an antiviral treatment trial were interviewed about a history of varicella. The clinical course of varicella was documented prospectively in all subjects. Serum samples that predated the acute illness were obtained from the US Navy's central serum storage facility for subjects who reported a previous episode of varicella. These stored samples were tested in parallel by enzyme-linked immunosorbent assay, latex agglutination, and Western blot for IgG antibodies to varicella-zoster virus (VZV). Paeticipants. —Twenty military personnel with varicella and a history of the disease. Setting. —A military hospital in San Diego, Calif. Main Outcome Measure. —Presence or absence of antibodies to VZV. Results. —Twenty (10.8%) of 184 adults with serologically confirmed acute varicella reported a prior history of varicella. The clinical course of these 20 patients did not differ from those with no history of varicella. Serum samples that had been collected a mean of 12.4 months (median, 12 months; range, 3 days to 34 months) before the incident episode were available for 19 subjects. All 19 serum samples lacked IgG antibodies to VZV. Conclusion. —A history of previous varicella infection in adults with varicella may not be reliable. True second episodes of varicella are probably rare in immunocompetent adults.