Second varicella infections: are they more common than previously thought?

Objective. To describe the epidemiology and clinical characteristics of varicella reinfections reported to a surveillance project. Methods. We investigated varicella cases reported to a surveillance project between January 1, 1995, and December 31, 1999-with more extensive investigation of cases reporting previous varicella with onset between January 1, 1998, and September 30, 1998-to provide a more detailed description of first and second varicella infections. A simple decision tree was used to assess the likelihood that reported first and second infections were varicella. Results. Among varicella cases reported to the surveillance project, 4.5% of cases in 1995 and 13.3% of cases in 1999 reported previous varicella. More than 95% of first infections were physician diagnosed, epidemiologically linked to another case, or had a rash description consistent with varicella; the same was true for reported second infections. People who reported reinfections were generally healthy. There was a family history of repeat infections in 45% of people who reported reinfections. Conclusions. Clinical varicella reinfections may occur more commonly than previously thought. Additional studies of the predictive value of a positive varicella history and laboratory studies of reported reinfections are indicated to guide varicella vaccination policy.