Patients with selective IgA deficiency could have various clinical presentations ranging from asymptomatic to severe respiratory or gastrointestinal tract infection, as well as autoimmune disease and allergic reactions. Selective IgA deficiency is relatively common in Caucasians, but it is rare in the Asian population, meaning it could be easily missed in the clinic. In this study, we report a 26-year-old man with a history of asthma and nephrotic syndrome. He presented with symptoms of pulmonary infection, and his condition quickly deteriorated to respiratory failure that required endotracheal intubation and mechanical ventilation. Sputum smear; sputum, blood, and bronchoalveolar lavage fluid culture; and metagenomic sequencing examination identified multiple mixed pathogens, including , and . Finally, he was diagnosed with selective IgA deficiency after a laboratory test detected an extremely low serum IgA level (<0.06 g/L). The patient died of septic shock and multiorgan failure despite aggressive management with a combination of antibiotics and supportive care. We report this case to remind clinicians about this rare disease in the Asian population. Patients with multisystem illnesses that are related to immune dysregulation, such as asthma or nephrotic syndrome, should be tested for immune system disorder. Rare and mixed pathogens should be considered during antibiotic selection in patients with selective IgA deficiency.