Pulmonary nocardiosis in patients with underlying pulmonary alveolar proteinosis: a case series and review of the literature

Pulmonary alveolar proteinosis (PAP) and pulmonary nocardiosis are relatively rare, their co-occurrence constitutes a clinically important comorbidity. Nocardia infection exhibits variable clinical manifestations, and carries a substantial risk of mortality in the absence of timely, pathogen-directed antimicrobial therapy. This study aims to summarize the clinical features of Nocardia infection in PAP patients. We present four confirmed cases of PAP complicated by Nocardia infection. These cases illustrate the distinct microbial species, disease courses and clinical outcomes. The duration of Nocardia infection among the four patients ranged from 3 months to over 2 years. All patients received anti-infection treatment guided by antimicrobial susceptibility testing (AST) results. Clinical outcomes included microbiological cure of infection, sustained clinical stability without progression, and all-cause mortality. In patients with PAP, the emergence of fever and new pulmonary opacities warrants strong clinical suspicion for Nocardia infection. Early initiation of pathogen-directed antimicrobial therapy is critical for infection control and enables subsequent PAP stabilization, clinical recovery, and the safe performance of whole-lung lavage.