Eruptive Pediatric Infections: Measles, Rubella, Chickenpox, Scarlet Fever — Differential Table

1. Comparative Table

2. Measles

• Prodrome of 3–4 days: temperature 39–40 °C, cough, rhinitis, conjunctivitis, photophobia.
• On days 2–3 — Koplik spots on the buccal mucosa opposite the 2nd lower molar (white grains on a hyperemic background) — pathognomonic.
• On days 4–5 — staged rash: face/behind the ears → trunk → extremities. The rash is maculopapular and tends to coalesce.
• Fading starting from day 3 of the rash — pigmentation and fine branny desquamation.
• Complications: pneumonia (#1 cause of death), encephalitis (1:1000), subacute sclerosing panencephalitis (SSPE, rare, delayed onset).
• Diagnosis — ELISA IgM, clinical presentation; measles is a reportable disease.
• Treatment — symptomatic + vitamin A 200,000 IU for 2 days (WHO) — ↓ mortality.
• Prevention — MMR vaccine at 12 months and 6 years of age.

3. Rubella

• Mild clinical course, low-grade fever.
• Fine maculopapular pink rash, starting on the face, spreading to the trunk within 24 hours; lasts 2–3 days; no desquamation.
• Enlargement of occipital, posterior cervical, and postauricular lymph nodes is characteristic.
• Arthralgia, especially in adolescents and women.
• Congenital rubella syndrome (CRS) when infected in the 1st trimester: cataract, congenital heart defects (PDA, pulmonary stenosis), deafness — Gregg's triad.
• Prevention — MMR.

4. Chickenpox

• Pathogen — VZV (Varicella-Zoster Virus).
• Fever + rash simultaneously; successive crops over 3–5 days.
• False polymorphism: macules, papules, vesicles, and crusts present in the same area. Pronounced itching.
• May involve mucous membranes (mouth, genitalia, conjunctiva).
• Complications: bacterial superinfection (streptococcal cellulitis), pneumonia (in adults and immunocompromised individuals), cerebellar ataxia, encephalitis, Reye's syndrome with aspirin use.
• Afterward — VZV remains in sensory nerve ganglia → reactivation = shingles (herpes zoster).
• Treatment: children < 12 years — symptomatic, acyclovir for severe cases or risk groups. Adolescents, adults, immunodeficiency — acyclovir 20 mg/kg 4 times/day (up to 800 mg 5 times/day).
• Prevention — vaccine (not in the National Immunization Schedule in Russia, but available).

5. Scarlet Fever

• Group A beta-hemolytic streptococcus, erythrogenic toxin.
• Acute onset: high fever, sore throat, vomiting.
• Fine punctate rash on a hyperemic background, denser in skinfolds (Pastia's lines — hemorrhagic linear streaks in the antecubital and popliteal fossae), flushed face with circumoral pallor (Filatov's sign).
• "Strawberry tongue" by days 3–5 (initially coated, then bright red with hypertrophied papillae).
• Lamellar desquamation on the palms and soles starting from the 2nd week.
• Complications: acute rheumatic fever (ARF), post-streptococcal glomerulonephritis, peritonsillar abscess, otitis media.
• Treatment — penicillins/amoxicillin for 10 days; in case of allergy — macrolides, cephalosporins.

6. Sudden Exanthem (Roseola Infantum)

• HHV-6, HHV-7. Children aged 6–24 months.
• High fever for 3–5 days without focal symptoms — a common cause of febrile seizures.
• Rash appears as the fever subsides: fine pink macules on the trunk and neck.
• Treatment is symptomatic, prognosis is favorable.

7. Infectious Erythema (Erythema Infectiosum)

• Parvovirus B19.
• Classic "slapped cheek" appearance — bright erythema on the cheeks, circumoral pallor.
• After a few days — "lace-like" rash on the extremities and trunk, may recur with sun exposure or stress.
• In adults — arthralgia/arthritis.
• During pregnancy (especially before 20 weeks) — risk of fetal hydrops, fetal demise.
• In hemolytic conditions — aplastic crisis (parvovirus has a tropism for erythroblasts).

8. Differential Diagnosis

• Allergic urticaria — urticarial elements, pruritus, rapid dynamics.
• Meningococcal infection — hemorrhagic rash, stellate, non-blanching on pressure (glass test). Urgent hospitalization, ceftriaxone.
• Enteroviral exanthem (Hand-Foot-Mouth disease) — vesicles on the palms, soles, and in the mouth.
• Toxic-allergic drug reactions.
• Infectious mononucleosis — maculopapular rash following amoxicillin administration.
• Kawasaki disease — fever > 5 days, polymorphous rash, conjunctivitis, lip cracking, strawberry tongue, cervical lymphadenopathy, desquamation of fingertips; coronary aneurysms!
• Lyme disease — erythema migrans (bull's-eye rash).
• Staphylococcal scarlatiniform syndrome (SSSS/TSS).

9. Isolation and Quarantine

• Measles — isolation until the 4th day after the onset of the rash; unvaccinated contacts — 21 days.
• Rubella — until 5 days from the onset of the rash; special vigilance needed around pregnant women.
• Chickenpox — until all crusts have dried (5–7 days from the last lesion).
• Scarlet fever — until 22 days from the onset of the disease (7 days with antibiotic therapy).

10. Vaccination (Russian National Immunization Schedule)

• Measles, mumps, and rubella (MMR) — 12 months and 6 years of age.
• By epidemiological indications — adults up to 35 years without vaccination records.
• Chickenpox — recommended, available outside the National Immunization Schedule (Varilrix).
• Passive immunoprophylaxis (immunoglobulin) for pregnant women and immunocompromised contacts.

11. FAQ

Can a vaccinated person get measles?
Yes, but extremely rarely (1–2%), more often with a mild, atypical course. A two-dose MMR schedule provides 97% protection.

How to distinguish chickenpox from nonbullous impetigo?
Impetigo presents with monopolymorphic yellowish crusts, usually on the face, without fever; chickenpox shows polymorphism all over the body accompanied by fever.

When is hospitalization mandatory?
Measles with pneumonia/encephalitis, chickenpox in adults and pregnant women, scarlet fever with complications, any hemorrhagic rash (suspected meningococcal disease).

Is scarlet fever dangerous in adults?
It occurs less frequently, but tends to have an atypical and severe course, with a higher risk of ARF.

Is it okay to "intentionally" expose a child to chickenpox?
No. The practice of "pox parties" is not recommended: complications in an infant are unpredictable. Vaccination is preferred.

See also: Asthma in children · Breastfeeding · Tuberculosis · HIV · Pediatrics Catalog