A 28-year-old woman with no previous diagnosis of diabetes developed diabetic ketoacidosis (DKA) one week after a 5-day trip to Cusco, Peru, at an altitude of 3,400 m. She presented with altered mental status, Kussmaul breathing, severe metabolic acidosis (pH 7.09, glucose 548 mg/dL, bicarbonate 6.1 mmol/L, anion gap 26 mEq/L), progressive respiratory symptoms, and hypoxemia. Chest CT showed multifocal consolidations with cylindrical bronchiectasis and air trapping; bronchoscopy revealed purulent secretions, and multiplex PCR identified parainfluenza virus, rhinovirus/enterovirus, Haemophilus influenzae, Staphylococcus aureus, Moraxella catarrhalis, and Candida albicans. She required mechanical ventilation for 4 days; standard treatment of DKA and antimicrobial therapy resulted in resolution of ketoacidosis within 48 hours. Entry HbA1c was 9.0%, C-peptide 2.1 ng/ml, negative autoantibodies, and subsequent insulin independence are consistent with an A-β+ ketosis-prone diabetes phenotype. Pulmonary function fully recovered within 6 months. The case highlights DKA induced by high-altitude exposure and polymicrobial pneumonia in the setting of previously unrecognized chronic dysglycemia.