A previously healthy 12-year-old girl presents to the ED with a 2-week history of cough that is productive of blood-tinged sputum and dyspnea. She was admitted to the hospital 2 weeks ago, soon after her symptoms developed, and was treated with 10 days of antibiotics. After completing the course, she reported mild improvement and was discharged. However, over the past 3 days, she has felt significantly worse, with increased cough, appearance of blood in her sputum, malaise, subjective fever, chills, posttussive emesis, and intermittent brown-colored urine. Physical examination reveals an ill-appearing girl whose axillary temperature is 37.6°C, heart rate is 120 beats/min, respiratory rate is 30 breaths/min, and oxygen saturation is 89% on 3 L oxygen per nasal cannula. She has tachypnea with coarse breath sounds bilaterally and inspiratory crackles in all lung fields. Musculoskeletal examination shows no findings of note. She does not have any oral ulcers, rash, or edema. Laboratory results include WBC count of 17.4×103/mcL (17.4×109/L) with 93% neutrophils, Hgb of 7.8 g/dL (78 g/L), platelet count of 616×103/mcL (616×109/L), BUN of 27 mg/dL (9.6 mmol/L), and creatinine of 1.8 mg/dL (159.1 mcmol/L). Urinalysis shows trace leukocyte esterase, 2+ protein, and 3+ blood, with 5 to 10 WBCs/high power field (hpf), 10 to 20 RBCs/hpf, and granular casts. The serum concentrations of complement components 3 and 4 are normal. Chest radiograph reveals extensive, diffuse, bilateral interstitial and alveolar infiltrates (Fig. 1). Blood, urine, and sputum cultures are obtained and empiric antibiotics initiated. Additional investigations reveal the diagnosis. Figure 1. Chest radiograph showing extensive, diffuse, bilateral interstitial and alveolar infiltrates. A 17-year-old boy presents with severe headache and progressive rash. He complains of chills, sore throat, anorexia, eye pain, and blurry vision. Before the onset of these symptoms, he was healthy and …