Predictive value of a history of varicella infection.

OBJECTIVE: To determine whether a history of previous varicella infection provides a reliable marker for prior infection. QUALITY OF EVIDENCE: MEDLINE was searched from January 1996 to May 2002 using the MeSH headings "varicella," "chickenpox" and "medical history taking." Recommendations in this paper are based on evidence from well designed cross-sectional studies. MAIN MESSAGE: Serologic testing is advised, rather than presumptive vaccination, for those with a negative or uncertain history of varicella; most will be immune. For those with a positive history of varicella, the advice given depends on the population. For populations at higher risk of varicella infection (eg, health care workers, pregnant women), routine serum testing is recommended. For low-risk populations, physicians could accept a positive history of varicella as a reliable indicator of immunity. CONCLUSION: Most studies found that patients' history of varicella had a high positive predictive value and a low negative predictive value. These findings suggest that a positive history of varicella is a reliable marker of disease while a negative history does not not predict lack of immunity.