Pediatrics (System-Integrated)

Pediatric fever without source: age-stratified workup

Clinical Overview and When to Suspect Serious Bacterial Infection in Febrile Infants

— 0–28 days (neonate): ~10–15% risk of serious bacterial infection (SBI: UTI, bacteremia, meningitis); ~2–4% invasive bacterial infection (IBI: bacteremia/meningitis). HSV always on the table.

— 29–60 days (young infant): ~8–10% SBI, ~1–2% IBI. Stratification tools (PECARN, Step-by-Step, Rochester) applicable.

— 61–90 days: ~5% SBI, IBI <1%. UTI dominates.

— 3–36 months: Most are viral. UTI prevalence 3–7%; occult bacteremia <1% in fully vaccinated. Occult pneumococcal disease nearly eliminated by PCV.

— >36 months: Rarely "without source" — focus on careful exam (otitis, pharyngitis, viral exanthem).

— Prematurity, perinatal complications, maternal GBS/HSV, prolonged ROM

— Immunocompromise, unvaccinated status, indwelling devices

— Ill appearance, poor feeding, lethargy, apnea, persistent tachycardia after fever defervescence

— Fever ≥39°C in 3–36 mo unvaccinated child

Board pearl: A "well-appearing" neonate ≤28 days with fever still gets the full septic workup including LP and empiric antibiotics + acyclovir — clinical reassurance does not exclude SBI in this age group. Step 3 vignettes will tempt you to discharge a calm-looking 14-day-old; do not.

Definition: Fever without source (FWS) = rectal temperature ≥38.0°C (100.4°F) in a child without localizing signs on history/exam after careful evaluation.

Epidemiology and risk by age strata (modern post-PCV13/Hib era):

Why age stratification matters: Immature immunity, blunted exam findings, and high-stakes pathogens (GBS, E. coli, Listeria, HSV in neonates) drive aggressive workup at <60 days regardless of how well the infant looks.

Red-flag historical features prompting fuller workup at any age:

Presentation Patterns and Key History

— Method matters: Rectal is gold standard <3 months. Axillary and temporal artery readings underestimate. Parental tactile fever counts as history but does not replace measurement.

— Height and duration: Higher temps (≥39°C) in 3–36 mo modestly raise SBI risk; duration <24 h does not lower risk in neonates.

— Antipyretic response does not predict bacterial vs viral etiology — common Step 3 distractor.

— Gestational age, NICU stay, maternal GBS status and intrapartum antibiotic prophylaxis adequacy

— Maternal HSV lesions, fever, chorioamnionitis, prolonged rupture of membranes >18 h

— Hyperbilirubinemia requiring readmission (associated with UTI)

— Sick contacts, daycare attendance, recent travel, tick/mosquito exposure

— Antibiotic use in prior 7 days (can mask culture yield)

— Recent immunizations (vaccine-related fever typically <48 h post-dose)

Key distinction: A viral URI does not exclude bacterial coinfection in infants <60 days; UTI and bacteremia have been documented in infants with bronchiolitis. Do not let an obvious viral source close the workup prematurely in the neonate.

Fever characterization:

Birth and perinatal history (critical <90 days):

Immunization status: Hib and PCV13/PCV15/PCV20 receipt dramatically lowers occult bacteremia risk; document doses received. Unvaccinated 3–36 mo child shifts management toward broader workup.

Exposure history:

Symptom review by system: Rhinorrhea/cough (viral URI but does NOT rule out concomitant UTI in <2 mo), vomiting/diarrhea (gastroenteritis vs early sepsis), rash (viral exanthem, meningococcemia, Kawasaki), urinary symptoms (uncommon presentation in infants — UTI presents as fever alone).

Feeding, activity, and output: Reduced PO intake, decreased wet diapers, sleepiness between fever spikes, paradoxical irritability when held ("paradoxical irritability" = meningismus equivalent in infants).

Physical Exam Findings and Hemodynamic Assessment

— Tools: Yale Observation Scale, Pediatric Assessment Triangle (appearance, work of breathing, circulation).

— Look for: quality of cry, reaction to stimulation, color, hydration, social engagement (smiling, tracking).

— In neonates ≤28 days, appearance is unreliable — ~65% of infants with SBI appear well.

— Tachycardia persisting after fever resolution is a sepsis red flag.

— Tachypnea: >60 (neonate), >50 (2–12 mo), >40 (1–5 yr) — may be the only sign of occult pneumonia or acidosis.

— Hypotension is a late finding in pediatric sepsis (compensated shock with normal BP is the rule).

— Capillary refill >3 sec, mottling, cool extremities = compensated shock.

— HEENT: Fontanelle (bulging = ICP/meningitis; sunken = dehydration), TMs, oropharynx (vesicles → HSV/herpangina), neck suppleness (Brudzinski/Kernig unreliable <12–18 mo).

— Skin: Petechiae below the nipple line concerning for meningococcemia; vesicular rash → HSV; strawberry tongue/conjunctivitis → Kawasaki if ≥5 days fever.

— Cardiopulmonary: Murmur (endocarditis rare but consider with persistent fever), focal crackles.

— Abdomen: Hepatosplenomegaly, RLQ tenderness (appendicitis often presents atypically in <5 yr).

— GU: Uncircumcised males <12 mo and all females <24 mo have highest UTI prevalence; examine for balanitis, vulvovaginitis.

— MSK: Pseudoparalysis of a limb → osteomyelitis/septic arthritis.

Step 3 management: Any infant with petechiae + fever, regardless of appearance, gets CBC, blood culture, coagulation studies, LP, and empiric ceftriaxone — meningococcemia can deteriorate within hours. Document hemodynamics serially.

General appearance — the single most predictive bedside finding in children >60 days:

Vital signs by age (know thresholds cold):

Focused systems exam:

Diagnostic Workup — Initial Labs and Imaging by Age Stratum

— CBC with differential, blood culture

— Urinalysis + urine culture by catheterization or suprapubic (bag specimens unacceptable for culture)

— CSF studies: cell count, glucose, protein, Gram stain, bacterial culture, HSV PCR, enterovirus PCR

— Inflammatory markers: CRP, procalcitonin (PCT)

— Consider HSV surface swabs (mouth, conjunctiva, rectum) + serum HSV PCR if vesicles, seizures, transaminitis, or maternal HSV

— CXR only if respiratory signs

— Stool studies if diarrhea

— AAP 2021 guideline / PECARN rule uses three criteria to identify low risk:

· Urinalysis negative (no pyuria, no LE, no nitrites)

· ANC ≤4,000–5,200/µL (varies by rule)

· Procalcitonin ≤0.5 ng/mL (or CRP ≤20 mg/L if PCT unavailable)

— All three negative → LP optional, may observe; any positive → LP and admit.

— Blood culture, urine culture, UA always obtained.

— UA + urine culture mandatory

— Blood culture and inflammatory markers if ill-appearing or high fever

— LP only if abnormal labs, ill appearance, or clinical concern

— UA + urine culture if febrile girl <24 mo, uncircumcised boy <12 mo, circumcised boy <6 mo, or fever ≥39°C without source

— CXR if T ≥39°C with WBC >20k or unexplained hypoxia/tachypnea

— Blood culture not routine in fully vaccinated children

Board pearl: Procalcitonin >0.5 ng/mL is the single best biomarker for IBI in young infants and is now embedded in AAP 2021 guidelines for 8–60 day olds — memorize this cutoff.

Neonates 0–28 days — full septic workup, no exceptions:

29–60 days — risk-stratified workup using validated tools:

61–90 days:

3–36 months, well-appearing, fully immunized:

Diagnostic Workup — Advanced and Confirmatory Studies

— Normal neonatal CSF WBC ≤15/µL (vs ≤5 in older children); protein up to 100 mg/dL acceptable in first month.

— Traumatic tap correction: subtract 1 WBC per 500–1000 RBCs (imperfect — clinical judgment trumps formula).

— Gram-negative rods on Gram stain → E. coli most likely; Gram-positive cocci in chains → GBS; Gram-positive rods → Listeria (broaden to ampicillin).

— Send HSV PCR and enterovirus PCR in any neonate with LP; enterovirus positivity allows safe antibiotic discontinuation in well-appearing infants with negative bacterial cultures at 24–36 h.

— UA positive = LE, nitrites, or >5 WBC/hpf (or >10 WBC/µL on enhanced UA).

— Catheter culture threshold: ≥50,000 CFU/mL of a single organism.

— Nitrite-negative does NOT rule out UTI in infants (short bladder dwell time).

— CXR for tachypnea, hypoxia, focal lung exam, or T≥39°C with WBC >20k.

— Renal/bladder US after first febrile UTI in children 2–24 mo (AAP).

— VCUG only if abnormal US, recurrent febrile UTIs, or atypical course.

— Neuroimaging before LP only if focal deficits, papilledema, immunocompromise, or altered mental status with concern for mass effect — routine CT before LP is not required.

CCS pearl: Order blood culture, urine culture (cath), CBC, CMP, CRP, procalcitonin, UA, LP with HSV/enterovirus PCR, and start empiric antibiotics + acyclovir — all in the first 60 minutes for a febrile neonate. The clock advances; do not "wait for cultures" before treating.

CSF interpretation pearls:

Urine studies:

Respiratory viral panel (RVP): Positive RSV, influenza, or SARS-CoV-2 reduces but does not eliminate SBI risk in neonates; UTI rate remains ~3–5% even with positive RVP.

Imaging:

Adjunctive: LFTs and HSV PCR if vesicles or seizures; lactate if shock suspected; coagulation studies with petechiae.

Risk Stratification — Validated Decision Rules

— Sequential evaluation: ill appearance → age ≤21 days → leukocyturia → PCT ≥0.5 → CRP >20 or ANC >10,000.

— Outperforms Rochester and Lab-score; sensitivity ~92%, NPV ~99.3%.

— Low risk = negative UA + ANC ≤4,090 + PCT ≤1.71 ng/mL.

— Sensitivity 97.7%, NPV 99.6%.

— 8–21 days: Full workup, admit, empiric antibiotics regardless of labs.

— 22–28 days: UA, blood culture, inflammatory markers, LP if any abnormal; admit with empiric antibiotics; may discharge at 24–36 h if cultures negative and well.

— 29–60 days: UA, blood culture, inflammatory markers; LP only if abnormal markers or positive UA; selective hospitalization.

— Temperature >38.5°C, ANC >4,000, CRP >20 mg/L, or PCT >0.5 ng/mL = abnormal.

Key distinction: AAP 2021 guidelines apply only to well-appearing, term, previously healthy infants 8–60 days. Premature infants, those with perinatal complications, focal infections, or technology dependence fall outside — default to full workup and admission.

Why rules exist: To safely identify low-risk infants 29–90 days who can avoid LP, IV antibiotics, and hospitalization.

Rochester Criteria (historical, 0–60 days): Well-appearing, term, previously healthy, WBC 5,000–15,000, bands <1,500, normal UA, stool WBC <5/hpf — sensitivity ~92% for SBI.

Step-by-Step (European, 22 days–90 days):

PECARN Rule (29–60 days):

AAP 2021 Clinical Practice Guideline (8–60 days, well-appearing, term ≥37 wk, no focal infection, no risk factors):

Inflammatory marker cutoffs (AAP):

Pharmacotherapy — Empiric Antibiotic and Antiviral Regimens

— Ampicillin 50–100 mg/kg IV q6–8h (covers Listeria, enterococcus, GBS) PLUS

— Gentamicin 4 mg/kg IV q24h OR cefotaxime 50 mg/kg IV q6–8h (if available; ceftriaxone avoided in neonates due to bilirubin displacement and calcium precipitation)

— Add acyclovir 20 mg/kg IV q8h if: vesicles, seizures, CSF pleocytosis with negative Gram stain, transaminitis, thrombocytopenia, maternal HSV, or ill appearance

— If meningitis suspected/confirmed: increase ampicillin to 300 mg/kg/day and add cefotaxime

— Ceftriaxone 50 mg/kg IV q24h (or 100 mg/kg/day if meningitis)

— Add vancomycin 15 mg/kg IV q6h if meningitis (cover resistant S. pneumoniae)

— Listeria coverage no longer routine after 28 days unless immunocompromised

— Outpatient febrile UTI: cefdinir, cefixime, or amoxicillin-clavulanate PO × 7–14 days

— Inpatient or toxic: ceftriaxone IV

— Occult bacteremia (rare): empiric ceftriaxone if blood culture positive while awaiting speciation

— Acetaminophen 10–15 mg/kg PO/PR q4–6h (max 75 mg/kg/day or 5 doses)

— Ibuprofen 10 mg/kg PO q6h — avoid <6 months and in dehydration/renal compromise

— Never aspirin in children (Reye syndrome)

Step 3 management: In a febrile neonate, start antibiotics within 1 hour of presentation — do not delay for LP if it cannot be done immediately. Draw blood culture first, then treat.

0–28 days (full coverage including Listeria, HSV):

29–60 days:

61–90 days, ill or high-risk: Ceftriaxone ± vancomycin per CSF findings.

3–36 months:

Antipyretics (supportive only, not diagnostic):

Duration: Continue empirics until cultures finalize at 24–48 h; tailor to organism. UTI 7–14 days, bacteremia 7–14 days, meningitis 14–21 days depending on pathogen.

Procedures — Lumbar Puncture, Catheterization, and Source Control

— Indications (FWS): All ≤28 days; 29–60 days with abnormal inflammatory markers or positive UA per AAP; any age with ill appearance, seizures, bulging fontanelle, petechiae, or pretreatment with antibiotics.

— Contraindications: Cardiopulmonary instability, focal neurologic deficits with suspected mass effect, coagulopathy (platelets <50k or INR >1.5), overlying skin infection.

— Technique: L3–L4 or L4–L5 interspace (line between iliac crests = L4); lateral decubitus or sitting; 22G spinal needle; opening pressure rarely measured in infants.

— Send: cell count + diff (tube 1 and 4 to detect traumatic tap), glucose, protein, Gram stain, culture, HSV PCR, enterovirus PCR; save extra for meningitis/encephalitis panel if needed.

— 5–8 Fr feeding tube or pediatric catheter, sterile technique.

— Suprapubic aspiration acceptable but less commonly performed.

— Bag specimens may be used for UA screening only — never for culture (contamination rates >60%).

— Abscess → I&D

— Septic arthritis → emergent ortho washout

— Mastoiditis with intracranial extension → ENT

— Topical lidocaine (LMX, EMLA) for LP and IV access (~30 min onset)

— Sucrose 24% oral for neonates undergoing procedures

— Avoid deep sedation in unstable infants

Board pearl: A "dry tap" or traumatic LP in a high-risk neonate does not waive empiric antibiotics + acyclovir — treat as if meningitis is present and repeat LP in 24–48 h or rely on cultures.

Lumbar puncture:

Urinary catheterization (gold standard <2 yr):

Blood culture: Minimum 1 mL in infants; ideally 2–4 mL. Single bottle (aerobic) sufficient. Yield improves with adequate volume.

Source control if identified:

Procedural sedation/analgesia:

Special Populations — Premature Infants and Complex Medical Conditions

— Use corrected gestational age for risk stratification — a 6-week-old born at 32 weeks is functionally a 38-week neonate.

— Higher baseline risk of late-onset sepsis from GBS, E. coli, coagulase-negative staph (if central line history), and Candida.

— Lower threshold for full workup and admission regardless of decision rule cutoffs.

— AAP 2021 algorithm excludes infants <37 weeks gestation.

— VP shunts → consider shunt tap and cover for Staph epidermidis (vancomycin + cefepime).

— Central venous catheters → blood cultures from line and peripheral site; cover for MRSA and gram-negatives including Pseudomonas (vancomycin + cefepime or piperacillin-tazobactam).

— Tracheostomy → CXR, tracheal aspirate culture; consider Pseudomonas coverage.

— G-tubes/J-tubes → assess insertion site for cellulitis.

— Sickle cell with fever ≥38.5°C → CBC, retic, blood culture, CXR, ceftriaxone IV within 1 hour; admit if <12 mo, toxic, hypoxic, WBC >30k or <5k, Hb <5, or unreliable follow-up. Functional asplenia → encapsulated organisms (pneumococcus, Hib, Salmonella).

— Febrile neutropenia (ANC <500): empiric cefepime or piperacillin-tazobactam ± vancomycin if mucositis/line infection.

— Renally dose aminoglycosides; monitor trough.

— Avoid ceftriaxone in neonates with hyperbilirubinemia (displaces bilirubin from albumin → kernicterus) — use cefotaxime.

Step 3 management: Any febrile child with a central line or VP shunt requires cultures from the device, broader empiric coverage (vancomycin + antipseudomonal beta-lactam), and inpatient admission until cultures finalize — even if well-appearing.

Prematurity (born <37 weeks):

Technology-dependent children:

Immunocompromise (oncology, primary immunodeficiency, transplant, sickle cell):

Renal/hepatic considerations:

Special Populations — Returned Travelers, Unvaccinated Children, Adolescents

— Malaria — thick and thin smears × 3 over 24–48 h; rapid antigen tests; falciparum is medical emergency.

— Enteric fever (typhoid/paratyphoid): blood and stool cultures; bradycardia relative to fever, rose spots, hepatosplenomegaly.

— Dengue: thrombocytopenia, hemoconcentration, plasma leak phase ~day 4–7 of illness.

— Tuberculosis: chronic fever, weight loss, exposure history; tuberculin skin test or IGRA + CXR.

— Always obtain detailed itinerary, prophylaxis adherence, food/water exposures, freshwater swimming (schistosomiasis, leptospirosis), animal contact.

— Restored risk of Hib epiglottitis, occult pneumococcal bacteremia, meningococcal disease, measles, pertussis.

— Lower threshold for CBC, blood culture, CXR in 3–36 mo with T ≥39°C.

— Consider broader differential: measles (Koplik spots, prodrome), pertussis (paroxysmal cough, post-tussive emesis).

— Confidentially screen for STIs (gonococcal/chlamydial pharyngitis, disseminated gonococcal infection, PID, epididymitis), pregnancy, IVDU (endocarditis), tattoos/piercings.

— Consider mononucleosis (EBV/CMV), acute HIV (mucocutaneous ulcers, lymphadenopathy, rash), inflammatory bowel disease, malignancy (lymphoma with B symptoms).

— Provide adolescent confidentiality per state law; parents typically excluded from STI/sexual health discussion.

Key distinction: A teenager with "FWS" rarely has the same differential as an infant — think infectious mononucleosis, acute HIV, IBD, occult abscess, endocarditis, and malignancy. Order EBV serologies, HIV 4th-gen, CBC with diff, ESR/CRP, and consider TTE if murmur or risk factors.

Returned international travelers with fever:

Unvaccinated or under-vaccinated children:

Adolescents (often miscategorized as "fever without source"):

Refugee/internationally adopted children: Screen for TB, hepatitis B/C, HIV, parasites, anemia, lead.

Complications and Adverse Outcomes

— Bacterial meningitis: mortality 5–10%; sensorineural hearing loss 10–30%, seizures, hydrocephalus, developmental delay.

— Untreated UTI in infants: renal scarring, hypertension, CKD; 10–15% risk of scarring after first febrile UTI.

— Bacteremia/sepsis: progression to septic shock, DIC, multiorgan failure within hours in neonates.

— HSV encephalitis (neonatal): Without acyclovir, mortality ~60% disseminated, ~15% CNS-only; with treatment, mortality drops to ~30% and ~6%, but long-term neurodevelopmental disability remains common.

— Antibiotic-associated adverse events: C. difficile colitis, allergic reactions, microbiome disruption.

— Hospital-acquired infections during admission.

— Procedural complications: post-LP headache (rare in infants), traumatic taps, catheter-associated UTI from catheterization.

— Family stress, cost, and missed work — particularly relevant in value-based care.

— Excess radiation from unnecessary CT scans.

— GBS late-onset disease: meningitis with high neurodevelopmental morbidity.

— E. coli neonatal sepsis: highest mortality among neonatal bacteremias.

— Meningococcemia: Waterhouse-Friderichsen syndrome (adrenal hemorrhage), purpura fulminans, limb amputation.

— Pneumococcus: post-meningitis deafness — obtain audiology at discharge and again at 4–6 weeks.

Board pearl: Hearing screen is mandatory after bacterial meningitis before discharge, and again 4–6 weeks later — early cochlear implant referral for severe loss preserves language development. Step 3 loves this follow-up detail.

Missed serious bacterial infection consequences:

Iatrogenic harms of overworkup:

Specific organism complications:

Long-term cognitive sequelae: ~25% of bacterial meningitis survivors have measurable deficits in attention, executive function, or academic performance.

When to Escalate Care — ICU, Consults, Inpatient Triage

— Septic shock requiring fluid resuscitation >40–60 mL/kg or vasopressor initiation

— Respiratory failure or oxygen requirement >FiO2 0.4

— Altered mental status, status epilepticus, signs of increased ICP

— Coagulopathy with active bleeding (DIC, purpura fulminans)

— Need for invasive monitoring or rapid clinical deterioration

— All febrile infants ≤28 days regardless of appearance

— 29–60 days with abnormal inflammatory markers or positive UA

— Any infant who received empiric IV antibiotics pending cultures

— Inability to tolerate PO, dehydration requiring IV fluids

— Concerning social situation, unreliable follow-up, distance from care

— Well-appearing 29–60 days with all negative inflammatory markers, awaiting 24-h culture data.

— Well-appearing 61–90 days with negative UA, normal labs, reliable caretakers, follow-up in 24 h

— Well-appearing fully vaccinated 3–36 mo with identified viral source or negative workup

— Infectious disease: complex pathogens, antibiotic failure, immunocompromised host, returned traveler

— Neurology: seizures, abnormal neuroimaging, encephalitis

— Neurosurgery: VP shunt infection

— Pediatric surgery: suspected appendicitis, abscess requiring drainage

— Child protective services: suspected abusive injury masquerading as FWS

CCS pearl: Sepsis bundle in pediatrics: recognize within 15 min, IV access + cultures + lactate within 30 min, antibiotics + 20 mL/kg isotonic bolus within 60 min, vasopressors (epinephrine first-line for cold shock; norepinephrine for warm shock) if fluid-refractory. Escalate to PICU.

PICU admission criteria:

Floor admission criteria:

Observation unit / short-stay (selected centers):

Outpatient management with close follow-up:

Consults:

Key Differentials — Same-Category (Infectious) Causes

— UTI: Most common occult bacterial infection in infants. E. coli >80%, then Klebsiella, Enterococcus, Proteus. Always check UA and culture by catheter.

— Occult bacteremia: Now <1% in vaccinated 3–36 mo; S. pneumoniae historically dominant, now non-vaccine serotypes, Salmonella, Staph aureus.

— Bacterial meningitis: GBS, E. coli, Listeria (neonates); pneumococcus, meningococcus, Hib (older infants/children).

— Pneumonia: Often occult in infants with only fever and tachypnea — CXR if T≥39°C and WBC >20k.

— Osteomyelitis/septic arthritis: S. aureus (including MRSA), Kingella in <4 yr — pseudoparalysis, refusal to bear weight.

— Bacterial enteritis: Salmonella, Shigella, Campylobacter, Yersinia — stool studies if diarrhea.

— Sinusitis, mastoiditis, retropharyngeal/peritonsillar abscess — careful HEENT exam.

— Enterovirus — summer/fall, can cause aseptic meningitis, hand-foot-mouth disease, myocarditis.

— HHV-6 (roseola): 3 days high fever, then defervescence with rash — classic 6–24 mo.

— Adenovirus: prolonged high fevers, can mimic Kawasaki.

— Influenza, RSV, parainfluenza, SARS-CoV-2, rhinovirus — confirm with multiplex PCR.

— EBV, CMV: mononucleosis in older children.

— HSV: neonatal disease (SEM, CNS, disseminated); always cover empirically when indicated.

— Bartonella (cat-scratch), Rickettsia (RMSF — fever + rash on wrists/ankles spreading centrally; doxycycline even in young children), Lyme, ehrlichiosis.

Key distinction: Roseola is diagnosed retrospectively when rash appears after 3 days of fever defervesce — premature labeling as roseola during the fever phase is a common pitfall and delays workup.

Bacterial sources to exhaust before declaring "no source":

Viral causes (most common cause of FWS overall):

Atypical and tick-borne:

Key Differentials — Other-Category (Non-Infectious) Causes

— Kawasaki disease: Fever ≥5 days plus 4 of 5: bilateral nonexudative conjunctivitis, oral changes (strawberry tongue, cracked lips), polymorphous rash, extremity changes (induration, desquamation), cervical lymphadenopathy >1.5 cm. Incomplete Kawasaki common in infants <12 mo — low threshold for echocardiogram. Treat with IVIG 2 g/kg + high-dose aspirin within 10 days to reduce coronary aneurysm risk from ~25% to <5%.

— Systemic JIA (Still disease): quotidian fever, salmon-pink evanescent rash, arthritis, hepatosplenomegaly, high ferritin.

— Macrophage activation syndrome: complication of sJIA, lupus — pancytopenia, falling ESR, high ferritin >10,000, hypofibrinogenemia.

— PFAPA: periodic fever, aphthous stomatitis, pharyngitis, adenitis — 3–6 day episodes every 3–8 weeks; responds dramatically to single steroid dose.

— Leukemia/lymphoma: fever from disease or neutropenia; look for pallor, bruising, lymphadenopathy, hepatosplenomegaly, bone pain, abnormal CBC (cytopenias or blasts).

— Neuroblastoma: abdominal mass, periorbital ecchymoses, opsoclonus-myoclonus.

— Recent vaccines (MMR fever 7–12 days post-dose; DTaP/PCV 24–48 h post-dose).

— Antibiotics, anticonvulsants → DRESS syndrome.

Board pearl: Fever ≥5 days in any child = think Kawasaki, especially incomplete forms in infants. Order CBC, ESR, CRP, albumin, ALT, UA, and echocardiogram if criteria suggestive — coronary aneurysms are time-sensitive to prevent.

Inflammatory and rheumatologic:

Oncologic:

Drug fever and immunization reaction:

Endocrine/metabolic: hyperthyroidism, adrenal crisis with intercurrent illness.

Factitious/Munchausen by proxy: fever only in caregiver's presence, multiple inconsistent presentations, normal labs — mandatory reporting concern.

Heat-related: environmental hyperthermia in bundled infants — recheck temp after unbundling.

CNS causes: central fever post-TBI/hemorrhage (rare in FWS context).

Discharge Planning, Secondary Prevention, and Long-Term Care

— Afebrile or improving trend, tolerating PO, hemodynamically stable

— Cultures negative at 24–36 h (some institutions extend to 48 h)

— Reliable caregivers, working phone, transportation, follow-up arranged

— No unaddressed positive lab finding or imaging abnormality

— Complete prescribed antibiotic course if UTI or bacteremia confirmed (typically 7–14 days PO).

— Antipyretics PRN with dosing chart (acetaminophen weight-based; ibuprofen if ≥6 mo).

— Probiotics not routinely indicated.

— Vaccination catch-up: ensure age-appropriate immunizations (Hib, PCV, MenACWY, rotavirus, influenza annually ≥6 mo, COVID-19) — review at every visit.

— UTI follow-up: renal/bladder US in 2–24 mo after first febrile UTI; VCUG if abnormal US or recurrent UTI; consider continuous antibiotic prophylaxis only for high-grade VUR or recurrent breakthrough UTI.

— Post-meningitis: audiology testing before discharge and at 4–6 weeks; developmental surveillance.

— Sickle cell: ensure penicillin prophylaxis through age 5, pneumococcal vaccines (PCV + PPSV23), meningococcal vaccines including MenB.

— Asplenia (functional or anatomic): lifelong vaccinations against encapsulated organisms; emergency antibiotic plan.

— Fever curve expectations, antipyretic limits, signs of dehydration, return precautions (lethargy, persistent vomiting, rash, decreased UOP, increasing fever, breathing difficulty).

— Avoid alternating acetaminophen and ibuprofen routinely — risk of dosing errors.

— Importance of completing full antibiotic course.

Step 3 management: Every infant with a first febrile UTI age 2–24 months gets a renal/bladder ultrasound; VCUG only if abnormal US or recurrent. Do not over-order VCUG — guidelines have narrowed indications.

Discharge criteria after negative workup:

Discharge medications:

Secondary prevention:

Caregiver education:

Follow-Up, Monitoring, and Counseling

— Neonates post-discharge from FWS admission: primary care visit within 24–48 h, then per routine well-child schedule (2, 4, 6 mo, etc.).

— 29–90 days discharged from ED: phone or in-person recheck in 24 h; in-person within 48–72 h if any concern.

— 3–36 mo with negative workup: return precautions, follow-up in 24–48 h if symptoms persist.

— Post-UTI: PCP visit in 1–2 weeks; imaging within 4–6 weeks of acute illness.

— Post-meningitis: neurology and audiology within 4–6 weeks; developmental assessment at 6 and 12 months.

— Growth (weight, length, head circumference) on standard curves

— Developmental milestones — formal screen at 9, 18, 24/30 months (ASQ, M-CHAT)

— Hearing rescreen post-meningitis or post-CMV

— Renal function and BP after pyelonephritis with scarring

— Fever myths: fever itself does not cause brain damage <42°C; febrile seizures (simple, 6 mo–5 yr) are usually benign and do not require chronic antiepileptics.

— Hydration emphasis, avoid bundling, daycare return after 24 h afebrile without antipyretics.

— When to call 911 vs urgent care vs primary care.

— Early intervention referral (state-specific Part C program) for any infant with sepsis, meningitis, or prolonged ICU stay

— Speech and language therapy if hearing loss or developmental delay identified

— Physical/occupational therapy if motor delays

Board pearl: Febrile seizures (simple type: <15 min, generalized, single in 24 h, ages 6 mo–5 yr) do not require LP, neuroimaging, EEG, or antiepileptics — only routine evaluation for the underlying fever source.

Follow-up cadence:

Monitoring parameters:

Counseling:

Rehabilitation considerations:

Anticipatory guidance: reinforce safe sleep, car seats, vaccinations, secondhand smoke avoidance, and household firearm safety at follow-up visits.

Ethical, Legal, and Patient Safety Considerations

— Parents/legal guardians provide consent for LP, catheterization, sedation, and blood draws.

— Document risks, benefits, and alternatives (including risks of not performing the workup).

— Emergency exception: life-threatening illness allows treatment without delay for consent — apply when sepsis suspected and guardian unavailable.

— Adolescents may consent independently for STI testing/treatment, mental health, and substance use services in most states (varies); document confidentiality limits.

— Suspected abusive head trauma, factitious disorder imposed on another, or neglect (e.g., repeated presentations with worsening untreated illness) → mandatory CPS report; physicians have legal immunity for good-faith reports.

— Document objective findings; do not confront caregivers accusatorily before report.

— Counsel non-judgmentally using strong-recommendation framing.

— Document refusal with AAP refusal form; reaffirm at each visit.

— Vaccine refusal alone is not grounds for CPS report but does change risk stratification for FWS.

— ED to floor: explicit communication of pending cultures, antibiotic timing, and parental concerns.

— Floor to outpatient: written discharge summary to PCP within 24 h; pending labs flagged with responsible clinician.

— Pending culture results post-discharge are a major safety event source — assign explicit ownership for follow-up.

Step 3 management: A pending blood culture at discharge requires a documented handoff: written instructions, defined responsible physician, callback plan, and parental return precautions. This is a tested patient-safety scenario.

Informed consent for procedures:

Mandatory reporting and child protection:

Vaccine refusal:

Transitions of care — high-risk handoff points:

Antibiotic stewardship: Avoid empiric broad-spectrum antibiotics in well-appearing low-risk infants meeting low-risk criteria — overuse drives resistance and C. difficile.

Health equity: Reliable follow-up assumes transportation, phone, language access, and financial stability — when these are absent, admit rather than discharge.

High-Yield Associations and Rapid-Fire Facts

— Girls <24 mo, uncircumcised boys <12 mo, circumcised boys <6 mo with fever

— UA + catheter culture; culture ≥50,000 CFU/mL

Board pearl: When a Step 3 stem mentions maternal genital lesions, neonatal seizures, transaminitis, or vesicles, the answer always includes IV acyclovir — do not wait for HSV PCR confirmation to start.

Neonatal sepsis triad of organisms: GBS, E. coli, Listeria — covered by ampicillin + gentamicin (or cefotaxime).

Why not ceftriaxone in neonates: Displaces bilirubin → kernicterus; precipitates with calcium-containing solutions → cardiopulmonary events.

HSV neonatal disease — three patterns: SEM (skin/eye/mouth), CNS, disseminated. All treated with IV acyclovir × 14 days (SEM) or 21 days (CNS/disseminated), followed by 6 months oral acyclovir suppression.

Procalcitonin >0.5 ng/mL = abnormal in AAP febrile infant pathway.

AAP febrile infant guideline ages: 8–60 days (excludes ≤7 days, premature, ill-appearing, or focal infection).

UTI screening thresholds:

First febrile UTI 2–24 mo: renal/bladder US; VCUG only if abnormal.

Sickle cell + fever ≥38.5°C: ceftriaxone within 1 hour, regardless of appearance.

Kawasaki criteria: CRASH and burn — Conjunctivitis, Rash, Adenopathy, Strawberry tongue, Hand/foot changes + fever ≥5 days.

Roseola: HHV-6; high fever × 3 days then rash post-defervescence; ages 6–24 mo.

Fever + petechiae below nipple line: rule out meningococcemia — full workup, ceftriaxone immediately.

RMSF: doxycycline regardless of age (overturned old tetracycline-age rule for life-threatening rickettsial disease).

Febrile seizure work-up: none routinely needed beyond fever source evaluation if simple type.

Bacterial vs viral CSF clues: Bacterial → ↑↑ WBC neutrophil-predominant, ↑ protein, ↓ glucose; viral → moderate WBC lymphocyte-predominant, mildly ↑ protein, normal glucose.

Neonatal CSF normals: WBC ≤15/µL, protein ≤100 mg/dL.

Bag urine for culture = never.

Board Question Stem Patterns

Key distinction: Many Step 3 stems hinge on age in days, not weeks — read carefully. A "28-day-old" and "29-day-old" trigger different AAP pathways.

Pattern 1 — The well-appearing neonate: "A 14-day-old term, previously healthy infant presents with rectal temp 38.4°C. He is feeding well and consolable. Vitals are normal." → Answer: Full sepsis workup including LP, empiric ampicillin + gentamicin/cefotaxime, admit. Distractors: discharge home, ceftriaxone (wrong neonatal antibiotic), observe without LP.

Pattern 2 — The 45-day-old well infant with negative UA: Stems will give you ANC, CRP, and PCT values. → Apply AAP 2021 algorithm. If all markers normal and UA negative → blood culture, observe (LP optional), may discharge with 24-h follow-up.

Pattern 3 — Petechiae + fever: Any age. → Full septic workup + ceftriaxone immediately; admit; consider meningococcemia.

Pattern 4 — Recently vaccinated 18-month-old with T 39.5°C: Fully vaccinated, well-appearing. → Limited workup: UA in appropriate age/sex; CXR if WBC >20k or respiratory symptoms; reassurance.

Pattern 5 — Fever × 5 days + rash + conjunctivitis: → Kawasaki disease; IVIG + high-dose aspirin + echocardiogram.

Pattern 6 — Sickle cell child with fever: → Ceftriaxone within 1 hour, blood culture, CBC, CXR; admit if any high-risk feature.

Pattern 7 — Returned traveler from sub-Saharan Africa: → Thick and thin smears for malaria.

Pattern 8 — Neonate with seizure and transaminitis: → IV acyclovir + ampicillin + cefotaxime; HSV PCR.

Pattern 9 — 9-month-old with first febrile UTI on cefdinir: "What imaging?" → Renal and bladder ultrasound.

Pattern 10 — Pending blood culture at discharge: → Document follow-up plan, assign responsible clinician, call family with results. Tests patient safety/transitions of care.

Pattern 11 — Bulging fontanelle + fever: → LP and empiric antibiotics; meningitis.

Pattern 12 — Roseola question: Defervescence followed by rash → reassurance, no further workup.

One-Line Recap

Pediatric fever without source is managed by strict age stratification: full workup and empiric antibiotics ± acyclovir for all neonates ≤28 days, validated decision rules (AAP 2021/PECARN/Step-by-Step) using UA, ANC, and procalcitonin for 29–60 days, selective workup for 61–90 days, and targeted UA/CXR for fully vaccinated 3–36 month olds — with always-on vigilance for UTI, meningitis, Kawasaki disease, and HSV in the right context.

Board pearl: Procalcitonin >0.5 ng/mL, AAP age cutoffs of 8/22/29/60 days, ceftriaxone avoidance in neonates, mandatory acyclovir triggers, and renal US after first febrile UTI are the five highest-yield testable facts — master these and you will answer the majority of Step 3 questions on this topic correctly.

0–28 days: Full septic workup (CBC, blood/urine/CSF cultures, HSV PCR, inflammatory markers) + ampicillin + gentamicin or cefotaxime + acyclovir when indicated; admit regardless of appearance.

29–60 days: Apply AAP 2021 algorithm using PCT >0.5, CRP >20, ANC >4,000, T >38.5 as abnormal markers; LP and admission when any abnormal or positive UA; ceftriaxone empirically.

61–90 days: UA + culture in all; broader workup if ill, high fever, or high-risk; selective admission.

3–36 months, fully vaccinated, well-appearing: UA in girls <24 mo, uncircumcised boys <12 mo, circumcised boys <6 mo; CXR if T ≥39°C and WBC >20k; otherwise reassurance and 24-h follow-up.