Fulminant Macrolide-Resistant Mycoplasma pneumoniae Pneumonia in a Young Adult: A Case Report

<i>Mycoplasma pneumoniae</i> commonly causes community-acquired pneumonia (CAP) in young adults, but it rarely leads to acute respiratory distress syndrome (ARDS). Macrolides are commonly used as the first-line treatment for <i>M. pneumoniae</i> pneumonia; however, the incidence of macrolide-resistant <i>M. pneumoniae</i> (MRMP) has increased, particularly in East Asia. There are few case reports of severe ARDS in adults caused by MRMP. Here, we present the case of a 27-year-old woman with severe MRMP pneumonia who required mechanical ventilation. Despite repeated negative rapid antigen tests for <i>M. pneumoniae</i>, the patient was suspected of having MRMP pneumonia based on the Japanese Respiratory Society (JRS) scoring system and bilateral pneumonia resistant to amoxicillin/clavulanate and azithromycin, which led to the administration of levofloxacin infusion. Hydrocortisone was administered as treatment for severe CAP. Lung-protective ventilation and prone positioning were implemented to manage severe ARDS. The patient's condition improved rapidly, with extubation on day 4 and discharge without complications on day 10. Previously, patients were treated based on positive test results. In this case, despite negative repeated rapid antigen tests and prior macrolide treatment, the probability of <i>M. pneumoniae</i> was evaluated, and treatment for MRMP was promptly initiated upon ICU admission. The diagnosis and treatment strategy resulted in early improvement. This case highlights the diagnostic approach for MRMP and the clinical course of severe ARDS associated with MRMP.