Describe rubella and the congenital rubella syndrome with its diagnosis and prevention.

The Virus and Postnatal Rubella

• A togavirus (rubivirus) — enveloped, icosahedral, with single-stranded positive-sense RNA; one serotype, and man is the only host
• It produces NO cytopathic effect in cell culture, and was classically detected by interference with a challenge virus
• Postnatal rubella is a mild illness — a low-grade fever with a fine discrete pink maculopapular rash beginning on the face and spreading, lasting about 3 days ("three-day measles"), with tender posterior auricular, suboccipital and posterior cervical lymphadenopathy, which is the most useful clinical sign
• Forchheimer spots (petechiae on the soft palate) may be seen; arthralgia and arthritis are common in adolescent and adult women
• Up to half of infections are subclinical, yet still infectious and still capable of causing fetal damage — which is why a history of "no rash" is worthless and serological status must be established

Congenital Rubella Syndrome

• The risk depends critically on the gestational age at maternal infection — the single most important fact for counselling
• Under 8 to 11 weeks — risk of defects approaches 90%; 11 to 16 weeks — about 20 to 35%, mainly deafness; after 16 to 20 weeks — deafness only, and the risk is small; after 20 weeks — defects are rare
• The classical triad — sensorineural deafness (the commonest single defect, and often the only one), cataract and other eye disease (retinopathy, glaucoma, microphthalmia), and cardiac defects, characteristically patent ductus arteriosus and pulmonary artery stenosis
• Other features — microcephaly and intellectual disability, growth restriction, hepatosplenomegaly, thrombocytopenia with a "blueberry muffin" rash from extramedullary haematopoiesis, and bone lucencies
• Late manifestations — diabetes mellitus, thyroid disease and progressive rubella panencephalitis, appearing years later
• Infected infants shed virus in urine and secretions for months and are a hazard to susceptible pregnant staff and visitors, so they must be isolated

Diagnosis and Prevention

• Maternal infection — rubella-specific IgM, or a fourfold rise in IgG in paired sera. IgG avidity testing is valuable: low avidity indicates recent primary infection and high avidity indicates past infection with no fetal risk
• Congenital infection in the infant — rubella IgM (which cannot cross the placenta and therefore must be the infant's own), persistence of IgG beyond the expected decline of maternal antibody, or virus detection in urine or a throat swab
• Vaccine — a live attenuated (RA 27/3) vaccine, given in India as measles-rubella (MR) in the Universal Immunisation Programme
• It is contraindicated IN pregnancy as a live vaccine, and pregnancy should be avoided for 28 days afterwards — though inadvertent vaccination in pregnancy has never been shown to cause congenital rubella syndrome and is not an indication for termination
• The strategy is to vaccinate children of both sexes to interrupt transmission, and to ensure women of childbearing age are immune by screening and vaccinating susceptible women postpartum or before conception

Applied Aspects

• Check rubella immunity before or early in pregnancy, and vaccinate susceptible women after delivery, which is the practical opportunity most often missed
• A history of rash or of "having had rubella" is unreliable; up to half of infections are subclinical and other illnesses mimic it, so only serology answers the question
• Use IgG avidity to date an infection when a pregnant woman is found to be IgM positive; false-positive IgM is common and has led to unnecessary terminations
• Isolate an infant with congenital rubella from susceptible pregnant staff and visitors, since shedding continues for months
• Test the hearing of any child with congenital rubella repeatedly; deafness may be the only defect and may not be apparent at birth
• India aims to eliminate congenital rubella syndrome through MR campaigns; coverage in adolescent girls and women of childbearing age is the limiting factor