Risk of infection following exposures to human parvovirus B19.

: In response to concern about the effect of human parvovirus B19 infection of the fetus, we have developed estimates of the risk of adults becoming infected following B19 exposures at home, in schools or day-care centers, and in hospitals. These estimates can then be used with other data to estimate the risk to the fetus of a B19 exposure during pregnancy. The risk to the fetus equals the rate of maternal susceptibility to infection times the rate of maternal infection following the specific type of exposure times the rate of fetal death following maternal infection. Data from studies of outbreaks of B19 associated erythema infectiosum and aplastic crisis suggest that the risk of infection among susceptible adults following household exposure to a B19 infected person is approximately 50% and following school exposures during outbreaks of erythema infectiosum is 20% to 30%. All susceptible school staff members, not just teachers, appear to be at risk for infection during outbreaks. Additional study is needed to determine the risk of infection following exposure to B19 infected patients in the hospital. Based on these and other data we can estimate that pregnant women whose serologic status is unknown have less than 2.5% chance of suffering fetal loss after household exposure and less than 1.5% chance after school exposure.