Examqo › Examqo library › Pediatrics › Paediatric infectious disease · IMLE
Viral exanthems in children
The rash illnesses are told apart by three clues: the timing of fever relative to the rash, where the rash starts and what it looks like, and the complication for which they are asked about.
Why it matters in the exam
The exam shows a child with fever and a rash and asks for the diagnosis or the expected complication. Each illness has a "signature": in measles — cough, coryza and conjunctivitis before a rash spreading down from the head, and Koplik spots; in roseola — high fever for 3–5 days and a rash only after the fever falls; in fifth disease — "slapped cheeks" and a lacy rash; in chickenpox — lesions at different stages at the same time.
Complications carry a lot of weight: parvovirus B19 causes an aplastic crisis in children with haemolytic anaemia and hydrops in the fetus; measles causes pneumonia, encephalitis and, much later, SSPE, and vitamin A deficiency makes it worse; rubella in pregnancy causes the congenital syndrome (deafness, cataract, heart defect); roseola causes febrile seizures. Israel has had measles outbreaks in recent years, so questions on isolation, post-exposure vaccination and IG are relevant.
In isolation and contagion questions, remember the basic rules: measles and chickenpox spread through the air and need airborne isolation, a child with chickenpox is contagious until all lesions have crusted, and exposure of a pregnant woman to rubella, chickenpox or parvovirus requires an immunity test and pregnancy follow-up.
Key points
- Measles: Koplik, cough-coryza-conjunctivitis, rash from the head downwards.
- Roseola: the rash follows defervescence after 3–5 febrile days.
- Parvovirus B19: slapped cheeks; aplastic crisis and fetal hydrops.
- Chickenpox: lesions at different stages; no aspirin.
- Measles exposure: MMR within 72 hours or IG within 6 days.
Summary table
| Disease (agent) | Key clue | Rash | Complication asked about |
|---|---|---|---|
| Measles | Cough, coryza, conjunctivitis; Koplik spots | Maculopapular, from the head downwards, after days of fever | Pneumonia, encephalitis, SSPE; vitamin A as treatment |
| Rubella | Post-auricular and occipital nodes | Fine, from the face downwards, fades within 3 days | Congenital rubella syndrome |
| Roseola (HHV-6) | High fever for 3–5 days in a well infant | Appears as the fever falls, on the trunk | Febrile seizures |
| Fifth disease (parvovirus B19) | "Slapped cheeks" | Lacy on the limbs | Aplastic crisis; fetal hydrops |
| Chickenpox (VZV) | Lesions at different stages at the same time | Itchy vesicles on a red base | Bacterial skin infection; no aspirin (Reye) |
| Hand, foot and mouth (enterovirus) | Mouth ulcers | Vesicles on the palms and soles | Dehydration; sometimes aseptic meningitis |
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Pediatrics, Medical licensing exam (IMLE), Family medicine, Dermatology and venereology.
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- AAP Red Book: Report of the Committee on Infectious Diseases, 2024–2027 edition — Measles; Rubella; Parvovirus B19; Human Herpesvirus 6 and 7; Varicella-Zoster; Enteroviruses
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Measles; Rubella; Parvovirus B19; Roseola; Varicella-Zoster Virus
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.