Pulmonary candidiasis, also known as bronchopulmonary candidiasis, is an acute, subacute, or chronic fungal infection of the lower respiratory tract caused by Candida albicans or other Candida species. Candida has a strong adhesion to mucosal tissues, with Candida albicans exhibiting the highest adhesive ability and pathogenic potential among Candida species. After being phagocytosed, Candida can still grow germ tubes inside macrophages, penetrate the cell membrane, and damage the macrophages. Furthermore, Candida can produce highly pathogenic water-soluble toxins, which may lead to shock. Pulmonary candidiasis is relatively rare in clinical practice. However, in recent years, infections caused by non-Candida albicans species (e.g., Candida tropicalis, Candida glabrata, and Candida krusei) have been on the rise, potentially due to the widespread use of antifungal drugs.
Clinically, candidiasis can be divided into two types, which also represent two stages of disease progression: bronchitis and pneumonia.
Bronchitis
This type presents with paroxysmal, irritating cough, accompanied by the expectoration of large amounts of white, foam-like sputum that resembles Styrofoam, sometimes mixed with blood streaks. As the disease progresses, the sputum becomes thick. Symptoms include wheezing, shortness of breath (worse at night), fatigue, and diaphoresis, often without fever. Chest X-rays typically show increased markings in the middle and lower lung fields.
Pneumonia
This type is characterized by chills, high fever, coughing up white, foamy mucus with a yeasty odor, and sometimes jelly-like sputum. Hemoptysis may also occur, and the clinical presentation closely resembles acute bacterial pneumonia. Chest X-rays reveal increased markings in the lower lobes of both lungs, with irregular linear opacities and scattered nodular opacities of varying sizes and shapes, resembling bronchopneumonia. Alternatively, diffuse, confluent, homogeneous infiltrates extending from the hilum to the periphery may be observed, sometimes forming cavities. The disease often involves both lungs or multiple lobes, with the lung apices rarely affected. Pleural effusion may occasionally develop as a complication.
Diagnosis
The diagnosis of pulmonary candidiasis requires the following:
- Microscopic examination of qualified sputum or bronchial secretions showing positive yeast pseudohyphae or hyphae in two separate samples.
- Fungal culture yielding Candida growth, with the same species identified in two separate cultures (excluding cases of hematogenous dissemination).
- Serum (1,3)-β-D-glucan antigen testing (G test) showing two consecutive positive results.
Definitive diagnosis, however, requires histopathological evidence.
Treatment
Mild cases often improve gradually after the removal of predisposing factors. Severe cases should be treated promptly with antifungal medications. Effective drugs include fluconazole, itraconazole, voriconazole, and posaconazole. The recommended dosage of fluconazole is 200 mg daily, with an initial loading dose of 400 mg. In severe cases, the dosage may be increased to 400 mg/day or higher (6-12 mg/kg/day). Amphotericin B can also be used for severe cases at a dosage of 0.5-1.0 mg/kg/day, but it is associated with significant toxicity. Echinocandins, such as caspofungin and micafungin, are also effective against Candida. The choice of antifungal agent should be guided by the patient’s clinical condition and fungal susceptibility testing results.