A 16-year-old Chinese American boy was brought to the emergency department by his parents after 1 day of headache, neck pain, fever, and fatigue. He denied any cough, vomiting, diarrhea, or weight loss, but he did report having an erythematous, papular skin rash along his hairline for the past 6 weeks. A dermatologist evaluated the rash and diagnosed impetigo. A trial of topical bacitracin and oral cephalexin temporarily improved the rash. He is a native of southern California, was previously healthy, was fully immunized, had no previous hospitalizations, and had no pertinent family history. It is of note that he had no ill contacts, had no recent illnesses, and denied travel outside of southern California. On examination, the patient had a temperature of 38.9°C, a heart rate of 78 beats per minute, a blood pressure reading of 110/46 mm Hg, a respiratory rate of 16 breaths per minute, and an oxygen saturation of 96% on room air. He was not ill-appearing. His lungs were clear to auscultation, and his heart sounds suggested a regular rate and rhythm with no murmurs. His abdomen was soft, nontender, nondistended, and without hepatosplenomegaly. On neurologic examination, he was alert and oriented with no focal findings; specifically, he had no nuchal rigidity or photophobia. His skin examination was notable for crusted excoriated papules along the anterior hairline and a solitary lesion on the right forearm. Laboratory evaluation of peripheral blood revealed a white blood cell (WBC) count of 11.3 k/mL, with a differential of 86.2% neutrophils, 7.2% lymphocytes, 4.8% monocytes, and 1.1% eosinophils; a hemoglobin level of 12 g/dL; a platelet concentration of 285 k/mL; a C-reactive peptide level of 19.9 mg/L; a erythrocyte sedimentation rate of 27 mm/hour, a sodium concentration of 139 mmol/L; a potassium level of 3.8 mmol/L; a chloride level of 105 mmol/L; a bicarbonate level of 27 mmol/L; a blood urea nitrogen concentration of 12 mg/dL; a creatinine level of 0.9 mg/dL; a glucose measurement of 98 mg/dL; an aspartate aminotransferase level of 23 U/L; an alanine aminotransferase concentration of 23 U/L; and a total bilirubin reading of 0.5 mg/dL. Noncontrast computed tomography of the head revealed normal results. A lumbar puncture (LP) was performed in the emergency department in response to the patient's persistent headaches. Cerebrospinal fluid (CSF) analysis revealed a WBC count of 187/mL, with a differential of 24% neutrophils, 40% lymphocytes, 33% monocytes, and 3% eosinophils; a red blood cell count of 13/mL; a protein level of 127 mg/dL; and a glucose reading of 47 mg/dL. A Gram-stain revealed many WBCs