These data suggest that a lag of several days occurs before IgG antibodies to varicella-zoster virus cross the placenta and equilibrate with the fetal circulation. The development of mild congenital varicella in the presence of placentally transferred maternal antibody has been demonstrated. The neonate may be at risk of developing severe varicella because the immune system is immature. In addition, the short incubation period suggests a large inoculum effect, presumably related to infection by maternal viremia rather than the respiratory route. In the neonate with a widespread, generalized vesicular exanthem and a history of either recent varicella or postnatal exposure, a diagnosis of chickenpox can usually be made with confidence on clinical grounds alone.
Greater difficulty is encountered when lesions are few or when there is no history of exposure.
Varicella-zoster virus can be isolated from vesicular lesions of otherwise healthy patients during the first 3 to 4 days of the eruption. Diagnosis can be accomplished by immunofluorescent staining of vesicular scrapings. These tests are reliable in determining immune status in healthy hosts but are not necessarily reliable in immunocompromised patients. The complement-fixation test is not sufficiently sensitive to be reliable in determining susceptibility in either case. The presence of specific IgM in one serum specimen suggests recent varicella-zoster infection.