Highly contagious paramyxovirus with prodromal cough/coryza/conjunctivitis and Koplik spots, followed by cephalocaudal maculopapular rash; vaccine-preventable.
Also known as: rubeola, morbillivirus, 10-day measles, first disease
Overview
Acute febrile viral illness caused by the measles virus (Morbillivirus, family Paramyxoviridae). Highly contagious via aerosolized droplets (R0 12-18). Characterized by the three Cs (cough, coryza, conjunctivitis), pathognomonic Koplik spots, and a cephalocaudal maculopapular rash.
Epidemiology
Eliminated in the US in 2000, but outbreaks recur in undervaccinated communities. Worldwide cause of childhood mortality (>100,000 deaths annually). One of the most infectious human pathogens; airborne particles remain infectious in a room for up to 2 hours after the index case leaves.
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Question 1Infectious DiseaseMedium
A 15-year-old has fever, cough, coryza, conjunctivitis, Koplik spots, and a descending maculopapular rash. Which of the following is the most likely diagnosis?
ARubella infection
BRoseola infection
CMeasles infection
DScarlet fever
Reveal answer & full explanation
Correct answer: C — Measles infection
ARubella infection
BRoseola infection
CMeasles infection✓
DScarlet fever
Why Measles infection is correct
Measles presents with the three Cs (cough, coryza, conjunctivitis), pathognomonic Koplik spots, and a maculopapular rash that spreads cephalocaudally.
It is highly contagious and prevented by MMR vaccination.
Complications include pneumonia, encephalitis, and the rare late subacute sclerosing panencephalitis.
Why the others are wrong
Rubella infection — Rubella is milder with tender postauricular lymphadenopathy and lacks Koplik spots; the Koplik finding distinguishes measles.
Roseola infection — Roseola causes 3 days of high fever in infants followed by rash as the fever breaks, not the prodrome with Koplik spots seen here.
Scarlet fever — Scarlet fever follows strep pharyngitis with a sandpaper rash and strawberry tongue, not the three Cs and Koplik spots of measles.
Question 2Infectious DiseaseEasy
A 4-year-old boy whose parents declined routine vaccinations is brought in for 4 days of high fever to 40°C, dry cough, runny nose, and red watery eyes without discharge. Today an erythematous maculopapular rash appeared at his hairline and spread down to his trunk. On oral exam there are 1-2 mm bluish-white papules on a red base on the buccal mucosa opposite the molars. The family returned from international travel 2 weeks ago. Which of the following is the most likely diagnosis?
AMeasles (rubeola)
BErythema infectiosum (fifth disease)
CRoseola (sixth disease)
DRubella (German measles)
Reveal answer & full explanation
Correct answer: A — Measles (rubeola)
AMeasles (rubeola)✓
BErythema infectiosum (fifth disease)
CRoseola (sixth disease)
DRubella (German measles)
Why Measles (rubeola) is correct
The classic triad of cough, coryza, and conjunctivitis (the three Cs) with high fever in an unvaccinated child after international travel is the hallmark prodrome.
Koplik spots (1-2 mm bluish-white papules on a red base on the buccal mucosa opposite the molars) are pathognomonic and precede the rash by 1-2 days.
The maculopapular rash begins at the face/hairline and spreads cephalocaudally, exactly as described.
Why the others are wrong
Rubella (German measles): milder prodrome with posterior auricular and suboccipital adenopathy; the rash is pinker and spreads faster, and there are no Koplik spots or prominent three Cs.
Roseola (sixth disease, HHV-6): high fever in a younger child that breaks first, with the rash appearing AS the fever defervesces; no Koplik spots or conjunctivitis.
Erythema infectiosum (fifth disease, parvovirus B19): a "slapped-cheek" facial rash with a lacy reticular pattern on the extremities and no febrile three-C prodrome or Koplik spots.
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Infants 6-12 months between waning maternal antibody and first MMR dose
Pathophysiology
Virus enters via respiratory epithelium, replicates in regional lymph nodes, and undergoes viremia with seeding of skin, mucosae, and reticuloendothelial system. Immune-mediated cytotoxicity produces rash and Koplik spots. Profound transient immunosuppression follows infection ('immune amnesia'), increasing susceptibility to other infections for months.
Clinical presentation
Symptoms
Prodrome (3-5 days): high fever (often 40 °C), cough, coryza, conjunctivitis (the three Cs), malaise
Koplik spots: 1-2 mm bluish-white papules on a red base on buccal mucosa opposite molars, 1-2 days before rash
Rash: erythematous maculopapular eruption beginning on face/hairline, spreading cephalocaudally over 3 days, becoming confluent and brownish before fading
Signs / physical exam
Conjunctival injection without purulent discharge
Cervical lymphadenopathy
Rash blanches early then darkens with desquamation
Classic findings
Three Cs + Koplik spots + cephalocaudal rash in an unvaccinated child.
Drug eruption / DRESS — Recent new medication; eosinophilia and facial edema
Enteroviral exanthem — Summer/fall, hand-foot-mouth pattern with vesicles
Diagnostic workup
Diagnostic criteria
Clinical case definition (fever, generalized maculopapular rash ≥3 days, plus cough/coryza/conjunctivitis) confirmed by IgM positive or RT-PCR positive.
Labs
Measles-specific IgM and IgG (acute and convalescent)
RT-PCR on nasopharyngeal swab, throat swab, urine, or blood — most sensitive within the first 5 days
Report immediately to public health (CDC nationally notifiable)
CBC: leukopenia and lymphopenia
Imaging
Chest x-ray if pneumonia suspected
Treatment
First-line
Supportive care: antipyretics, hydration, isolation (airborne precautions for 4 days after rash onset)
Vitamin A: 200,000 IU PO on days 1 and 2 (50,000 IU if <6 months, 100,000 IU if 6-11 months) — WHO/AAP recommend for all children with measles; reduces mortality and ocular complications
Post-exposure prophylaxis: MMR vaccine within 72 hours OR immunoglobulin within 6 days for high-risk contacts (infants <6 months, pregnant women, immunocompromised)
Routine prevention (ACIP)
MMR vaccine — first dose 12-15 months, second dose 4-6 years
MMR is a live attenuated vaccine; contraindicated in pregnancy and severe immunocompromise
Outbreak / accelerated schedule
Infants 6-11 months traveling internationally: one early MMR dose (does not count toward routine series)
Catch-up: two MMR doses ≥28 days apart
Second-line / adjunct
Ribavirin has been used anecdotally for severe disease but is not standard
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.