An illness with acute onset of diffuse (generalized) maculo-papulovesicular rash without other apparent cause.
An acute illness with
An acute illness with diffuse (generalized) maculo-papulovesicular rash, AND
Two probable cases that are epidemiologically linked would be considered confirmed, even in the absence of laboratory confirmation. In vaccinated persons who develop varicella more than 42 days after vaccination (breakthrough disease), the disease is almost always mild with fewer than 50 skin lesions and shorter duration of illness. The rash may also be atypical in appearance (maculopapular with few or no vesicles). Laboratory confirmation of cases of varicella is not routinely recommended; laboratory confirmation is recommended for fatal cases and in other special circumstances.