Spontaneous remission of Pneumocystis jirovecii pneumonia followed by severe pulmonary nocardiosis in a patient with HIV infection: A case report.

We describe a rare case of spontaneous remission of Pneumocystis jirovecii pneumonia (PCP) in a 42-year-old patient with human immunodeficiency virus (HIV) infection, followed by severe pulmonary nocardiosis. To our knowledge, this is the first report of spontaneous remission of PCP in a completely untreated patient with HIV infection. The patient, a bisexual Japanese man, presented with fever and anorexia and had a history of non-compliance with antiretroviral therapy (ART) for 13 years. PCP was initially suspected on the basis of imaging and laboratory findings, but the patient refused further evaluation and treatment. Surprisingly, the evidence of PCP infection disappeared without intervention. Four months later, the patient was diagnosed with severe pulmonary nocardiosis caused by Nocardia beijingensis, which was confirmed by bronchoscopy and culture. Antibiotic therapy and ART resulted in significant clinical improvement. Based on this case, we propose that N. beijingensis infection may contribute to spontaneous remission of PCP, possibly through production of antimicrobial substances and induction of granulocyte-macrophage colony-stimulating factor. On the other hand, fluctuations in immune function, particularly variability in CD4⁺ T lymphocytes, may also contribute. This report highlights the complex interplay between opportunistic infections in immunocompromised patients. These findings may provide valuable insights into the management of PCP.