Serologic surveys have found that 30% to 60% of adults in the United States have serum antibodies against B19, indicating prior infection (657,658). Surveys of pregnant women in other countries show B19 seroprevalence rates of 35% in Barcelona, Spain, 40% in Japan, 53% in Kuwait, 64% in Melbourne, Australia, 65% in Denmark, and 81% in Stockholm, Sweden (659,660,661,662,663,664). The virus is transmitted primarily by B19-infected respiratory secretions. Transmis-sion through transfusions of blood or blood products such as pooled factor VIII or IX concentrates is uncommon. B19 is found in the blood of 1 in 20,000 to 1 in 50,000 donors, but the incidence can be as high as 1 in 260 during epidemic years (665). To reduce the risk of iatrogenic transmission, major producers of plasma derivatives have voluntarily started quantitative measurements of B19 DNA to keep it under 10,000 genome copies per mL in the manufacturing pools (653,665). The incubation period of parvovirus B19 is 4 to 14 days, but it can be as long as 21 days. Infections are more common in late winter and spring in temperate climates, and epidemics usually occur every 4 or 5 years (666).

About 1% of susceptible pregnant women without known exposure to B19-infected persons seroconvert each year in the United States. Rates of 1.5% to 6.8% for acute gestational B19 infections have been reported from other countries (659-661,667). Higher rates are encountered during epidemic periods (661). During a large erythema infectiosum outbreak in Connecticut, pregnant women were tested for serologic evidence of recent B19 infection. Infection rates among exposed susceptible pregnant women were 16% for school teachers, 9% for day care workers, and 9% for homemakers (668). Attack rates of 36% to 38% were documented among susceptible nursing staff who were exposed to patients with sickle-cell anemia and aplastic crisis at a children’s hospital (669). However, another study of health care workers under similar circumstances showed no transmission of B19 from patients to susceptible staff members (670).

A study of 30,946 pregnant women from three regions in Denmark conducted between November 1992 and June
1994 found that the presence of B19 IgG correlated with a woman’s number of siblings, having a sibling close in age (within 2 years), number of children, and occupational exposure to children. The risk of seroconversion to B19 during pregnancy increased by threefold to sevenfold depending on the number of children at home, and having children 6 to 7 years of age was associated with the highest rate of gestational B19 infection (661).

Half or more of acute B19 infections of adults are subclinical (653,666). Erythema infectiosum is the most commonly identified B19-related condition. This illness is seen primarily in children, and its most characteristic feature is a facial exanthem (i.e., slapped-cheek appearance). The rash is lacy or reticulated, spreads to the trunk and extremities, and fades within 2 weeks. Recrudescence of the rash is observed with stimuli such as temperature changes, sunlight, or emotional stress. Pruritic, petechial, purpuric, vesicular, or erythema multiforme types of rashes are possible with acute B19 infection (653,666,671,672).

In addition to erythema infectiosum, acute B19 infections in otherwise healthy adults can manifest with influenza-type illnesses and symmetric polyarthropathies (e.g., polyarthralgias, polyarthritis). B19-associated joint disease is more common in women, affecting 50% to 80% of those with symptoms (673). The hands are most often involved, but pain, stiffness, and swelling can also involve the wrists, ankles, and knees (653,666). Rheumatoid factor may be positive transiently; therefore the illness could be misdiagnosed as early rheumatoid arthritis (674). B19 infections in compromised patients can result in transient aplastic crises, chronic anemia, and viral-induced hemophagocytic syndrome (653).