Virology: congenital rubella: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Virology: congenital rubella

Sample item

A term newborn has bilateral cataracts, a continuous machinery murmur, sensorineural hearing loss and a blueberry muffin rash. The mother had a mild rash with suboccipital lymphadenopathy at 8 weeks of gestation. Which investigation best confirms congenital infection?

AA single haemagglutination inhibition titre in the mother at deliveryBA single rubella IgG level in the infant's serumCRubella-specific IgM or rubella RNA by RT-PCR in the infantDRubella IgG in the mother's serum collected now

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Rubella-specific IgM or rubella RNA by RT-PCR in the infant

Maternal IgG crosses the placenta, so IgG in a newborn does not prove infection of the baby. IgM does not cross the placenta, so rubella-specific IgM or viral RNA in the infant's blood, urine or throat confirms congenital rubella. Infection in the first trimester carries the highest risk of defects.

Option by option

A. A single haemagglutination inhibition titre in the mother at delivery
A single maternal titre cannot date the infection or prove fetal infection.
B. A single rubella IgG level in the infant's serum
Maternal IgG is transferred across the placenta, so a single infant IgG value cannot confirm infection.
C. Rubella-specific IgM or rubella RNA by RT-PCR in the infant (correct)
Correct. IgM is made by the fetus and viral RNA shows active infection.
D. Rubella IgG in the mother's serum collected now
Maternal IgG now shows only past exposure and cannot show that the fetus was infected.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Rubella-specific IgM or rubella RNA by RT-PCR in the infant. Maternal IgG crosses the placenta, so IgG in a newborn does not prove infection of the baby.

Why is "A single haemagglutination inhibition titre in the mother at delivery" not the answer?

A single maternal titre cannot date the infection or prove fetal infection.

Why is "A single rubella IgG level in the infant's serum" not the answer?

Maternal IgG is transferred across the placenta, so a single infant IgG value cannot confirm infection.

Why is "Rubella IgG in the mother's serum collected now" not the answer?

Maternal IgG now shows only past exposure and cannot show that the fetus was infected.

What concept does this question test?

It tests Virology: congenital rubella in Microbiology. IgM does not cross the placenta, so rubella-specific IgM or viral RNA in the infant's blood, urine or throat confirms congenital rubella. Infection in the first trimester carries the highest risk of defects.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Virology: congenital rubella?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.