Congenital parvovirus B19 infection

• Common childhood illness, often associated with a rash, or ‘slapped-cheek’ appearance.
• Is a fetal risk if maternal infection occurs prior to 20 weeks gestation:
  • ~10% excess risk of fetal death
  • ~3% risk of hydrops fetalis if maternal infection between 9-20 weeks
• Unlike other congenital infections, which can cause a wide range of abnormalities, parvovirus is associated specifically with hydrops fetalis.
  • Does not appear to be associated with long-term developmental sequelae in those that don’t develop hydrops.
• Treatment is available for hydrops, which can significantly improve survival.

Parvovirus infects red blood cell precursors. If fetal infection occurs this can result in fetal anaemia, which is what causes hydrops.

• Routine screening in pregnant women is not recommended.
• Test in pregnant women exposed to possible parvovirus infection.
• Test in pregnant women with features of possible hydrops fetalis on USS.
  • Parovirus testing is not recommended as part of testing if other possible congenital abnormalities are seen, as it is specifically associated with hydrops (and occasionally transient pleural or pericardial effusions).
  • Testing not recommended if isolated polyhydramnios.

Asymptomatic and within one week of exposure:

• Request “Parvovirus serology” and note date of exposure on lab form
  • Parvovirus IgGpositive
    • Evidence of immunity.
    • No further action required.
  • Parvovirus IgGnegative
    • Susceptible to infection.
    • Repeat parvovirus serology in 4 weeks or if symptoms develop to look for seroconversion.

Symptomatic:

• Request “Parvovirus serology”
  • Parvovirus IgM & IgG positive
    • Suggestive of acute infection.
    • Refer to maternal fetal medicine specialist.
  • Parvovirus IgM positive, IgG negative
    • Possible early acute infection.
    • Repeat serology in 2 weeks to look for IgG seroconversion (confirms acute infection).
  • Parvovirus IgM & IgG negative
    • No evidence of parvovirus being cause of symptoms.
    • Repeat serology 4 weeks after exposure.

• Parvovirus IgM negative, IgG positive
  • Probable past infection/immunity.
  • A small proportion of people do not mount a detectable IgM response. If there was a clear history of exposure and suggestive symptoms, discuss with clinical microbiologist regarding further testing.
    • May include testing of booking sample to look for seroconversion, or maternal blood PCR.

Step 1: confirm maternal infection: request “Parvovirus serology”

• Parvovirus IgG negative
  • Excludes maternal infection and therefore fetal infection as cause of hydrops.
  • No further parvovirus testing required.

• Parvovirus IgG positive
  • Confirms maternal infection at some stage
  • Continue to step 2. Further testing should be under the guidance of a maternal fetal medicine specialist.

Step 2: if confirmation of fetal infection is required (e.g. to confirm parvovirus as cause of hydrops): parvovirus PCR on amniotic fluid

• Excellent sensitivity – a negative result makes parvovirus the cause of hydrops very unlikely
• Excellent specificity – a positive result confirms fetal parvovirus infection

Parvovirus blood PCR

• Reserved for specialist use, as serology is the first line tool for diagnosis.
• Used in certain situations where serology is inconclusive.

Parvovirus testing as part of a ‘TORCH’ screen, or if other, non-hydrops, abnormalities seen on antenatal USS

• Because parvovirus produces the specific condition of hydrops, it should not be included as part of a general screen if other abnormalities are seen.