Defining the Role of Fungi in Respiratory Infections: Clinical Features, Underlying Conditions, and Imaging Findings

Abstract

Abstract
Background: Pulmonary fungal infections are increasingly recognized as significant contributors to respiratory disease, particularly among immunocompromised patients. Despite their clinical importance, differentiating colonization from true invasive infection remains a major diagnostic challenge.

Methods: In this multicenter cross-sectional study (June 2024–May 2025), 568 adults with suspected lower respiratory tract infections from three tertiary hospitals in Tehran were evaluated. Respiratory specimens underwent microscopy, culture, and galactomannan (GM) testing. Yeast isolates were identified using multiplex PCR (YEAST PLEX). Clinical characteristics, comorbidities, and radiological findings were analyzed.

Results: Fungi were detected in 342 patients (60.2%). Fungal-positive patients were older than negatives (52.4 ± 15.7 vs. 49.1 ± 17.3 years, p = 0.038). Candida species (56.4%) predominated, followed by Trichosporon (24.9%), Aspergillus (12.9%), Pneumocystis (3.2%), and other molds. Hemoptysis was significantly more common in fungal-positive patients (21.1% vs. 12.4%, p = 0.019), whereas cough, fever, and pleuritic chest pain showed no differences. Cavitary or nodular infiltrates were associated with fungal positivity (31.6% vs. 14.6%, p < 0.001), while ground-glass opacities and consolidations were not. GM testing was positive in 73.8% of Aspergillus-positive patients and 9.3% of controls (p < 0.001), with higher mean optical density indices in infected cases.

Conclusion: Pulmonary fungal infections are common and underrecognized in respiratory disease. BAL sampling, GM testing, and radiologic correlation provide valuable tools for distinguishing true infection from colonization, particularly in older and immunocompromised patients.