7 · Infectious Disease & Viral Exanthems

The classic childhood rashes and fevers — pattern recognition wins.

Illness	Hallmark
Measles (rubeola)	3 C's (cough, coryza, conjunctivitis) + Koplik spots → cephalocaudal maculopapular rash; high fever; vitamin A; highly contagious
Rubella	Mild rash + posterior auricular/suboccipital nodes; teratogenic (congenital rubella)
Roseola (HHV-6)	High fever 3–5 d → rash appears as fever breaks; infant; febrile seizure risk
Erythema infectiosum (fifth, parvovirus B19)	"Slapped cheek" → lacy reticular rash; aplastic crisis in sickle cell; fetal hydrops
Hand-foot-mouth (coxsackie A)	Oral ulcers + vesicles on hands/feet; supportive
Varicella	Crops of lesions in different stages ("dew drop on a rose petal"); vaccine-preventable
Scarlet fever (GAS)	Sandpaper rash, strawberry tongue, circumoral pallor; treat GAS
Mononucleosis (EBV)	Adolescent; fatigue, exudative pharyngitis, posterior nodes, splenomegaly; +monospot; avoid contact sports; ampicillin → rash
Kawasaki disease	Fever ≥5 d + 4 of: conjunctivitis, oral changes, rash, extremity changes, cervical node; risk = coronary aneurysm; treat IVIG + aspirin, echo

⭐ Kawasaki is the can't-miss: fever ≥5 days plus the CRASH-and-burn criteria → IVIG + aspirin within 10 days to prevent coronary artery aneurysms (aspirin here is an exception to the Reye-syndrome rule).

Bacterial & spirochetal infections (Lange Ch 42)

Infection	Key points
Group A strep sequelae	GAS causes pharyngitis, scarlet fever, and impetigo; untreated pharyngitis → acute rheumatic fever (Jones criteria) and post-strep glomerulonephritis (antibiotics prevent RF, not PSGN).
Cat-scratch disease	Bartonella henselae; tender regional lymphadenopathy after a kitten scratch; usually self-limited (azithromycin for significant disease).
Lyme disease	Erythema migrans (target rash) after a tick bite; later arthritis, carditis, facial palsy. Doxycycline (amoxicillin for young children).
Congenital syphilis	Maternal syphilis; snuffles, rash (palms/soles), Hutchinson teeth, saddle nose, saber shins; screen all pregnancies; penicillin.
Bone/joint infection	Osteomyelitis / septic arthritis — S. aureus most common; a child who won't bear weight or move a joint with fever needs urgent workup (ESR/CRP, blood culture, aspiration/MRI).
Invasive bacteria	Meningococcus (petechiae/purpura → emergency), pneumococcus, and (in unvaccinated) H. influenzae type b.

Parasitic & fungal infections (Lange Ch 43)

Infection	Key points
Pinworm (Enterobius)	Nocturnal perianal itching; "tape test" for eggs; treat the child and household (albendazole/pyrantel), repeat in 2 weeks.
Giardia	Watery, foul, greasy diarrhea + bloating after daycare/camping/well water; treat with metronidazole/tinidazole.
Scabies	Intensely itchy burrows (web spaces, wrists; infants on palms/soles/scalp); permethrin, treat close contacts and launder bedding.
Head lice (pediculosis)	Itchy scalp with nits on hair shafts; topical permethrin; no "no-nit" school exclusion needed.
Tinea	Ringworm — tinea capitis (needs oral antifungal, e.g., griseofulvin/terbinafine), corporis/pedis topical.
Candida	Oral thrush (nystatin), candidal diaper dermatitis (topical antifungal); consider immunodeficiency if severe/persistent.

More viral infections (Lange Ch 40)

Virus	Key points
Congenital CMV	The leading infectious cause of congenital hearing loss and a cause of microcephaly, periventricular calcifications, and petechiae ("blueberry muffin"). Diagnose by CMV PCR (urine/saliva) in the first 3 weeks; antiviral (valganciclovir) for symptomatic disease.
Mumps	Parotitis; complications include orchitis, aseptic meningitis, and hearing loss; vaccine-preventable (MMR).
Influenza	Abrupt fever, myalgia, cough; oseltamivir within 48 h for high-risk; annual vaccine ≥6 mo. Avoid aspirin (Reye syndrome).
Enterovirus / coxsackie	Summer-fall febrile illness, hand-foot-mouth, herpangina, aseptic meningitis, myocarditis.
Rocky Mountain spotted fever (rickettsial)	Tick exposure; fever, headache, then a rash starting on wrists/ankles (including palms/soles) spreading centrally; treat empirically with doxycycline (all ages) — don't wait for confirmation.
Molluscum / warts	Common self-limited poxvirus/HPV skin lesions; usually no treatment needed.

⭐ Two "treat now, confirm later" rules: a febrile child with a wrist/ankle rash and tick exposure gets doxycycline for RMSF immediately; and any newborn who fails the hearing screen should be evaluated for congenital CMV within the first 3 weeks (after that you can't distinguish congenital from postnatal infection).

Pediatric HIV (Lange Ch 41)

Perinatal (vertical) transmission is the main pediatric route; maternal ART with viral suppression in pregnancy + infant ARV prophylaxis + avoiding breastfeeding (in resource-rich settings) reduces transmission to <1–2%.
Diagnosis in infants: maternal antibody crosses the placenta, so antibody tests are unreliable early — use HIV DNA/RNA PCR (virologic testing) in the first months of life.
Treatment: ART is recommended for all with HIV, started early; it is lifelong (latent virus is not eradicated). Goal = viral suppression to preserve immunity and prevent transmission.
Opportunistic-infection prophylaxis: Pneumocystis (PCP) prophylaxis with TMP-SMX for at-risk infants/low CD4; keep immunizations current (some live vaccines depend on immune status).