Mild togavirus rash illness in children and adults but devastating to the fetus when contracted in the first trimester (congenital rubella syndrome).
Also known as: German measles, 3-day measles, third disease, rubella virus, congenital rubella syndrome, CRS
Overview
Acute viral illness caused by rubella virus (Togaviridae). Mild in postnatally acquired cases but a major teratogen in early pregnancy, causing congenital rubella syndrome (CRS) with cataracts, sensorineural deafness, and cardiac defects.
Epidemiology
Declared eliminated in the US in 2004, but cases still occur in unvaccinated travelers. Globally remains a leading vaccine-preventable cause of birth defects. ACIP recommends two-dose MMR for all children.
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Question 1Infectious DiseaseMedium
A 26-year-old woman who recently returned from international travel presents with 2 days of a pink maculopapular rash that began on her face and spread to her trunk, along with low-grade fever and new pain in her wrists and knuckles. On exam she has tender posterior auricular and suboccipital lymphadenopathy and mild conjunctivitis. She is not pregnant and has no documented vaccination history. Which of the following is the most appropriate test to confirm the diagnosis?
AEBV heterophile antibody test
BParvovirus B19 IgM serology
CMeasles (rubeola) IgM serology
DRubella-specific IgM serology
Reveal answer & full explanation
Correct answer: D — Rubella-specific IgM serology
AEBV heterophile antibody test
BParvovirus B19 IgM serology
CMeasles (rubeola) IgM serology
DRubella-specific IgM serology✓
Why Rubella-specific IgM serology is correct
The vignette is classic rubella: a pink, rapidly spreading maculopapular rash that begins on the face, tender posterior auricular and suboccipital adenopathy (the most useful clinical discriminator), polyarthralgia of the small joints in a young woman, and recent travel in an unimmunized patient.
Acute postnatal rubella is confirmed by a positive rubella-specific IgM (or a fourfold rise in paired IgG titers); RT-PCR of a nasopharyngeal or oral swab is an acceptable alternative. Rubella is nationally notifiable, so laboratory confirmation should be pursued and reported to public health.
Why the others are wrong
Parvovirus B19 IgM serology confirms erythema infectiosum, which is on the differential and can cause arthralgia, but it produces a slapped-cheek facial flush with a later reticular ('lacy') rash and lacks the posterior auricular and suboccipital adenopathy seen here.
Measles (rubeola) IgM serology confirms measles, which has a more severe prodrome, Koplik spots, and a slower cephalocaudal rash; the prominent posterior auricular and suboccipital nodes plus the mild course point to rubella instead.
EBV heterophile antibody test confirms infectious mononucleosis, which causes posterior cervical adenopathy and pharyngitis but not this facial-onset maculopapular rash or the small-joint arthralgia of rubella.
Question 2Infectious DiseaseMedium
A 24-year-old woman presents with a 2-day history of a pink maculopapular rash that began on her face and spread to her trunk, accompanied by tender posterior auricular and suboccipital lymphadenopathy and new aching in her wrists and knees. She recently returned from a 3-week trip abroad, works as a hospital ward clerk, and is 8 weeks pregnant. Review of her records shows she never completed her childhood vaccination series and has no documented rubella immunity. Rubella IgM returns positive. Which of the following is the strongest risk factor for her acquiring this infection?
ALack of rubella immunization
BHospital occupational exposure
CRecent international travel
DPregnancy in first trimester
Reveal answer & full explanation
Correct answer: A — Lack of rubella immunization
ALack of rubella immunization✓
BHospital occupational exposure
CRecent international travel
DPregnancy in first trimester
Why Lack of rubella immunization is correct
Susceptibility to rubella is determined almost entirely by immune status; a person with documented two-dose MMR immunity is protected regardless of exposure intensity.
Being unimmunized (no vaccine-induced or natural immunity) is the necessary precondition for infection, and all other listed factors only matter because they increase the chance of an exposure reaching a susceptible host.
ACIP recommends two-dose MMR for all children and screening with postpartum vaccination for non-immune women of childbearing age precisely because lack of immunity is the dominant modifiable driver of disease.
Why the others are wrong
Recent international travel is a real exposure risk in the post-elimination US, where most cases are travel-associated, but it raises risk only in someone already susceptible; an immune traveler does not contract rubella.
Hospital occupational exposure without immunity is a recognized risk, but it is again a modifier of exposure, not the underlying determinant; immune staff are protected.
Pregnancy in first trimester dramatically raises the risk of severe fetal harm from congenital rubella syndrome, roughly 85% in the first 12 weeks, but it does not increase the mother's likelihood of acquiring the infection itself.
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Virus enters via respiratory droplets, replicates in nasopharyngeal lymphoid tissue, then disseminates by viremia. In pregnancy, transplacental transmission infects the fetus; earlier gestational age confers higher risk of multiorgan teratogenesis through interference with mitotic and angiogenic processes.
Clinical presentation
Symptoms
Prodrome (often absent in children): low-grade fever, malaise, mild coryza, sore throat 1-5 days before rash
Drug eruption — Recent new drug, eosinophilia, no posterior auricular nodes
Scarlet fever — Strep throat, sandpaper rash, no adenopathy in the rubella distribution
Enteroviral exanthem — Summer/fall, often with hand-foot-mouth pattern
Diagnostic workup
Diagnostic criteria
Clinical syndrome plus positive IgM or RT-PCR. Congenital rubella: positive viral isolation, RT-PCR, or persistent rubella-specific IgG beyond expected maternal antibody decline.
Labs
Rubella IgM and IgG (paired sera) — IgM positive in acute infection
RT-PCR on nasopharyngeal or oral swab
Rubella IgG screening for pregnant women at first prenatal visit
CBC: lymphocytopenia, atypical lymphocytes possible
Report to public health (nationally notifiable)
Imaging
Fetal ultrasound for suspected congenital rubella with growth restriction, microcephaly, cardiac defects
Postnatal echocardiography in infants with suspected CRS (PDA, peripheral pulmonary stenosis)
Treatment
First-line
Supportive: antipyretics, NSAIDs for arthralgia
Droplet precautions for 7 days after rash onset
MMR vaccine (live, 2-dose schedule) — first dose 12-15 months, second 4-6 years; women of childbearing age should be screened and vaccinated postpartum if non-immune
MMR is contraindicated in pregnancy and should be avoided for 28 days before conception
Pregnancy exposure
Test maternal IgG and IgM; if susceptible and exposed, monitor closely
Counsel on CRS risk by trimester: first 12 wk highest risk (~85%); risk falls sharply after 20 wk
Immune globulin does NOT reliably prevent fetal infection
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