What is the appropriate diagnostic work‑up and empiric treatment for a 1‑year‑old infant presenting with fever, a tender cervical lymph node (neck lymphadenitis) and markedly elevated C‑reactive protein (~200 mg/L) without other focal findings?

Diagnostic Work-Up and Empiric Treatment for a 1-Year-Old with Fever, Cervical Lymphadenitis, and CRP ~200 mg/L

This infant requires immediate evaluation for incomplete Kawasaki disease (KD), bacterial lymphadenitis, and serious bacterial infection, with urgent echocardiography and laboratory testing to guide treatment decisions.

Immediate Diagnostic Priority: Rule Out Kawasaki Disease

Incomplete Kawasaki disease is the most critical diagnosis to exclude in this clinical scenario. A 1-year-old with prolonged fever and cervical lymphadenopathy as the dominant feature represents a classic diagnostic pitfall—these children are frequently misdiagnosed as having bacterial lymphadenitis, with subsequent rash and mucosal changes mistakenly attributed to antibiotic reactions 1. Infants are at particularly high risk for incomplete KD and coronary artery abnormalities 1.

Kawasaki Disease Evaluation Algorithm

• Obtain urgent echocardiography to assess for coronary artery abnormalities (Z-score ≥2.5 for LAD or RCA), decreased LV function, mitral regurgitation, or pericardial effusion 1.
• Check complete laboratory panel: CBC with differential, CRP, ESR, albumin, ALT, and urinalysis 1.
• Apply the incomplete KD algorithm: With fever ≥5 days and CRP ≥3.0 mg/dL (this patient has ~200 mg/L = 20 mg/dL), assess for ≥3 supplementary laboratory criteria: anemia for age, platelets ≥450,000 after day 7, albumin <3.0 g/dL, elevated ALT, WBC ≥15,000/mm³, or urine ≥10 WBC/hpf 1.
• Treat with IVIG 2 g/kg if incomplete KD criteria are met OR if echocardiogram is positive, even without meeting full clinical criteria 1.

The markedly elevated CRP of 200 mg/L strongly supports systemic inflammation and meets the threshold for proceeding with the incomplete KD evaluation pathway 1.

Concurrent Evaluation for Serious Bacterial Infection

While evaluating for KD, simultaneously assess for bacterial causes given the high CRP:

Mandatory Cultures Before Antibiotics

• Obtain catheterized urine specimen for urinalysis and culture—urinary tract infection is the most common serious bacterial infection in this age group (5-7% prevalence) and must be excluded 2, 3.
• Draw blood culture before any antibiotic administration 2, 3.
• Perform CBC with differential to assess for leukocytosis, neutrophilia, or concerning cytopenias 2.

Lymph Node-Specific Assessment

• Ultrasound the cervical lymph node to differentiate reactive adenopathy from suppurative bacterial lymphadenitis requiring drainage 2, 4, 5.
• Assess for fluctuance, overlying skin changes, and node characteristics (size >2 cm, matted, hard nodes raise concern for atypical infection or malignancy) 2, 4.

Chest Radiograph Consideration

• Obtain chest X-ray if any respiratory signs are present (tachypnea, cough, retractions) or if WBC >20,000/mm³, as occult pneumonia occurs in ~7% of febrile infants and rises with markedly elevated inflammatory markers 2.

Empiric Antibiotic Therapy Decision

Do NOT start antibiotics until after cultures are obtained unless the child appears toxic or hemodynamically unstable 2, 3.

If Antibiotics Are Indicated (Toxic Appearance or Unstable):

• Cover Staphylococcus aureus and Group A Streptococcus, the causative organisms in 40-80% of acute unilateral bacterial cervical lymphadenitis 4, 5.
• Empiric regimen: Vancomycin (for MRSA coverage) plus ceftriaxone or ampicillin-sulbactam 4, 5.
• Adjust based on culture results and clinical response 4, 5.

If Child Appears Well:

• Defer antibiotics pending culture results if biomarkers and clinical assessment suggest low risk for invasive bacterial infection 3.
• Arrange close follow-up within 24-48 hours with strict return precautions for worsening fever, toxic appearance, or inability to maintain hydration 2, 3.

Critical Diagnostic Pitfalls to Avoid

• Never dismiss this as simple bacterial adenitis without excluding Kawasaki disease—the combination of fever, unilateral cervical lymphadenopathy, and subsequent development of rash/mucosal changes is a well-documented presentation of KD that is frequently missed 1.
• Do not assume normal platelet count rules out KD—thrombocytosis typically occurs after day 7 of illness; early in the disease, platelets may be normal or even low 1.
• Never rely on bag-collected urine—only catheterized or suprapubic specimens are acceptable for culture 2, 3.
• Do not start antibiotics before obtaining blood and urine cultures—this compromises diagnostic yield 2, 3.

Additional Considerations

MIS-C Screening

• Obtain SARS-CoV-2 PCR and serology if there is any epidemiologic link to COVID-19 exposure in the preceding 2-6 weeks 1.
• MIS-C presents with broader age range, prominent GI symptoms, shock, and lower platelet counts than classic KD, but can develop coronary artery abnormalities 1.

Atypical Mycobacterial Infection

• Consider nontuberculous mycobacterial (NTM) lymphadenitis if the node becomes chronic, fails to respond to standard antibiotics, or develops sinus tract formation 1.
• NTM cervical adenitis is most common in children <3 years old and typically requires excisional surgery rather than antibiotics alone 1.

Disposition and Follow-Up

• Admit for inpatient management if the child appears ill, has unstable vital signs, meets criteria for incomplete KD requiring IVIG, or if reliable outpatient follow-up cannot be ensured 2.
• If discharged, ensure follow-up within 24-48 hours with clear instructions to return immediately for worsening symptoms 2, 3.
• Repeat echocardiography at 2 weeks and 6-8 weeks if KD is diagnosed or strongly suspected 1.