Laboratory Studies
Most patients with parvovirus B19 (B19V) infection do not require laboratory studies because symptoms are mild and the illness resolves over 5-7 days.
-
Parvovirus serology (anti–parvovirus B19 immunoglobulin M [IgM] and immunoglobulin G [IgG] antibodies) can be determined using enzyme-linked immunoassay (ELISA), radioimmunoassay, or immunofluorescence. Results of IgM testing are particularly difficult to interpret. Standardization between laboratories is lacking. Even in a single laboratory, sensitivity and specificity are partly determined by operator skills. High-level viremia in acutely infected persons may cause virus-antibody complexes, which will result in a false-negative IgM test result. [37] In this setting, polymerase chain reaction (PCR) may be a better diagnostic modality.
-
PCR testing for parvovirus B19 is routinely available with increased sensitivity level. However, contamination and false-positive results are noted risks that lead to confusing interpretation. Low levels of B19 DNA may detectable for more than 4 months in serum after acute infection and for years in other tissues. [38, 39] . This test, a more useful clinical tool to diagnose chronic infection, detects viral DNA present in the blood or other tissues/fluids. [22] The interpretation, especially as it pertains to pregnant women is uncertain. [21, 25] The diagnosis of acute or chronic infection should be made on the basis of standard DNA hybridization or quantitative (real-time) PCR in combination with serologic assays for B19-specific IgG, IgM, or both. [8] Monitoring the quantitative PCR viral load in neonates with congenital parvovirus infection helps direct follow-up and the need for transfusions.
-
During experimental infection of volunteers, IgM antibodies were detected 10-12 days after inoculation, and IgG antibodies were detected at 2 weeks. [40] Ninety percent of patients with classic erythema infectiosum rash had IgM antibodies detected at initial presentation and IgG antibodies by day 7. [9] IgM remains detectable for months and IgG for life. [9, 8]
-
In patients with evidence of clinically significant anemia or transient aplastic crisis (TAC), obtain a CBC count with reticulocyte count.
Patients infected with parvovirus B19 have a low reticulocyte count (0-1%).
In an aplastic crisis, hemoglobin levels drop below the patient's baseline by at least 2 g/dL.
IgM antibodies are usually present by day 3 of illness or the time of hematopoietic nadir. IgG antibodies are detectable around the time of the recovery of erythrogenesis. [8, 9, 28, 19]
Parvovirus B19 PCR demonstrates high level viremia during TAC. [8]
-
If a pregnant woman is exposed to parvovirus B19, obtain IgG and IgM serology as soon as possible. [25, 22]
Positive IgG results and negative IgM results indicate past infection (no risk to fetus).
Positive IgG and IgM results indicate infection within the last 7-120 days (possible risk to fetus).
Negative IgG results and positive IgM results indicate acute infection (higher risk to fetus).
Negative IgG and IgM results indicate that the mother is not immune and that no evidence of acute infection is noted. In this case, repeat the tests in 3 weeks. Subsequent development of IgM indicates an acute infection.
No standards have been established to evaluate parvovirus B19 PCR on maternal blood; low levels may be detected long after clinical infection. [39] PCR may be performed on fetal serum of amniotic fluid to detect virus. [21]
Imaging Studies
Routine imaging is not necessary.
Fetal ultrasonography may be useful in detecting hydrops. The timing and frequency of ultrasonography surveillance for infected pregnant women have not been conclusively determined. [22]
-
Note the right side of this boy's face displaying signs of erythema infectiosum, or Fifth disease. Image courtesy of CDC.
-
Elementary school child with Fifth Disease. Image courtesy of CDC.
