Pediatric Infectious Disease
The exanthems, sore throats, and airway emergencies that fill pediatric wards
The childhood exanthems
Pattern recognition. The rash's timing relative to fever, where it starts, and its companions (mucosal spots, lymph nodes, tongue changes) identify most childhood exanthems at the bedside.
| Disease | Cause | Key features | Complications and pearls |
|---|---|---|---|
| Measles | Paramyxovirus | Prodrome of cough, coryza, conjunctivitis (3 Cs); Koplik spots; morbilliform rash spreading from hairline and face downward | Pneumonia (leading cause of death), otitis media, encephalitis, SSPE years later; give vitamin A |
| Rubella (German, 3-day measles) | Togavirus | Pink maculopapular rash face → trunk; tender postauricular and suboccipital nodes; mild in children | Congenital rubella: sensorineural deafness, cataracts, PDA, blueberry-muffin lesions |
| Roseola (exanthem subitum, sixth disease) | HHV-6 | 3–5 days of high fever in a well-appearing infant; rose-pink truncal rash as the fever breaks | Classic cause of febrile seizures |
| Fifth disease (erythema infectiosum) | Parvovirus B19 | Slapped-cheek facial rash, then lacy reticular rash on the extremities | Aplastic crisis (sickle cell, spherocytosis), hydrops fetalis, adult arthropathy |
| Varicella | VZV | Pruritic vesicles in crops, all stages at once ("dew drop on a rose petal"); starts on trunk and face and spreads out | Bacterial superinfection (GAS, S. aureus), pneumonia in adults, cerebellar ataxia; reactivates as zoster |
| Hand-foot-mouth disease | Coxsackievirus A16, enterovirus 71 | Oral vesicles and ulcers plus vesicles on palms and soles | Self-limited |
| Herpangina | Coxsackievirus A | Fever with vesicles and ulcers on the posterior oropharynx (soft palate, tonsillar pillars) | Self-limited |
| Scarlet fever | Group A strep with erythrogenic (pyrogenic) exotoxin | Sandpaper blanching rash, strawberry tongue, circumoral pallor, Pastia lines in skin folds; desquamation follows | Penicillin or amoxicillin to prevent rheumatic fever |
Koplik spots (blue-white "grains of salt" on a red buccal base) appear 1–2 days before the rash and are pathognomonic for measles.
Mechanism pearls. Parvovirus B19 binds the P antigen on erythroid precursors, halting erythropoiesis, which is why chronic hemolysis tips into aplastic crisis. Children with fifth disease are no longer contagious once the rash appears. Avoid aspirin in varicella (Reye syndrome). Measles spreads by airborne transmission; exposed unvaccinated contacts can receive MMR within 72 hours or immune globulin within 6 days.
Otitis media, strep pharyngitis, and rheumatic fever
Acute otitis media. The top organisms are S. pneumoniae, nontypeable H. influenzae, and M. catarrhalis, often after a viral URI. The exam shows a bulging, erythematous tympanic membrane with reduced mobility on pneumatic otoscopy. First-line therapy is high-dose amoxicillin; use amoxicillin-clavulanate if amoxicillin was given in the past 30 days or purulent conjunctivitis coexists (a nontypeable H. influenzae clue). Observation is an option for selected older children with mild, nonsevere disease.
Group A strep pharyngitis. Fever, tonsillar exudates, tender anterior cervical nodes, and no cough or coryza (Centor criteria). Confirm with a rapid antigen test or throat culture (in children, back up a negative rapid test with culture). Treat with penicillin or amoxicillin, mainly to prevent rheumatic fever. A muffled "hot potato" voice, trismus, and uvular deviation signal a peritonsillar abscess needing drainage.
Antibiotics prevent rheumatic fever but do not prevent post-streptococcal glomerulonephritis, which can follow throat or skin infection.
Acute rheumatic fever follows GAS pharyngitis by 2–4 weeks through type II hypersensitivity (molecular mimicry). Diagnosis needs evidence of recent strep (elevated ASO or anti-DNase B) plus two major criteria, or one major and two minor (fever, arthralgia, raised ESR or CRP, prolonged PR interval). The JONES major criteria:
- Joints: migratory polyarthritis of large joints, the most common manifestation
- O (the heart): carditis, a pancarditis centered on the mitral valve; the most serious manifestation (mitral regurgitation acutely, mitral stenosis chronically)
- Nodules: subcutaneous
- Erythema marginatum
- Sydenham chorea
Treat the acute illness with anti-inflammatories plus penicillin to eradicate residual strep, then give long-term secondary prophylaxis with intramuscular benzathine penicillin.
Bronchiolitis and airway emergencies
RSV bronchiolitis is the leading cause of infant hospitalization in the US. Infants under 2 years present in winter with wheeze, tachypnea, retractions, and nasal flaring after a URI. Management is supportive: oxygen if saturation stays below 90%, hydration, and nasal suctioning. Bronchodilators, steroids, and antibiotics are not routinely helpful. Palivizumab has been the prophylaxis for high-risk infants (prematurity, chronic lung or heart disease); the long-acting antibody nirsevimab now protects infants entering their first RSV season.
| Feature | Croup (laryngotracheobronchitis) | Epiglottitis |
|---|---|---|
| Cause | Parainfluenza virus | H. influenzae type b in the unvaccinated |
| Picture | Barking, seal-like cough and inspiratory stridor after coryza; child often playful | High fever, toxic appearance, drooling, dysphagia, tripod posture |
| Neck film | Steeple sign | Thumbprint sign |
| Treatment | Dexamethasone; nebulized racemic epinephrine for stridor at rest | Secure the airway in a controlled setting, then IV antibiotics |
In suspected epiglottitis, do not depress the tongue or examine the throat and do not upset the child: agitation can precipitate complete obstruction. Keep the child with the parent until the airway is secured.
The febrile infant: UTI and meningitis
Serious bacterial infection. In the febrile young infant, rule out serious bacterial infection; under the AAP 2021 guideline, well-appearing febrile infants 8 to 21 days old get blood, urine, and CSF cultures and empiric antibiotics; at 22 to 28 days, LP is required if inflammatory markers are abnormal and may be done after shared decision making if they are normal. Infants under 8 days and any ill-appearing infant get the full evaluation.
UTI (usually E. coli) is the most common occult bacterial source. Obtain urine by catheterization (or suprapubic aspiration) for culture; bag specimens are unreliable. A renal and bladder ultrasound follows the first febrile UTI in infants and toddlers, and a VCUG for vesicoureteral reflux is added when the ultrasound is abnormal or UTIs recur or are atypical.
| Feature | Neonate (under 1 month) | Older infant and child |
|---|---|---|
| Organisms | Group B strep, E. coli, Listeria | S. pneumoniae, N. meningitidis |
| Empiric therapy | Ampicillin (covers Listeria) plus ceftazidime or cefepime (cefotaxime is unavailable in the US); ampicillin plus gentamicin if meningitis is not suspected | Ceftriaxone plus vancomycin (resistant pneumococcus) |
After meningitis. Close contacts of meningococcal disease receive chemoprophylaxis (rifampin, ciprofloxacin, or ceftriaxone). Sensorineural hearing loss is the most common sequela of bacterial meningitis, so every survivor gets a hearing evaluation.