Pulmonary candidiasis, also known as bronchopulmonary candidiasis, is an acute, subacute， or chronic lower respiratory tract mycosis caused by Candida albicans or other Candida species. Candida has the characteristic of adhering to mucosal tissues. Candida albicans has a particularly strong adhesion to tissues, so its pathogenicity is stronger. After being phagocytosed, Candida can still grow germ tubes in macrophages, penetrating the cell membrane and damaging macrophages. Candida can also produce highly pathogenic water-soluble toxins, causing shock. In recent years, infections caused by Candida tropicalis, Candida glabrata, and Candida krusei have increased, which may be related to the wide application of antifungal drugs
Etiology
Candida is widely present in nature and is conditionally pathogenic. In clinical practice, Candida albicans is the most common, and there are more than 16 types of pathogenic Candida, in which Candida tropicalis, Candida glabrata, Candida parapsilosis, and Candida krusei are more common. It is generally known that there are some Candida complexes, such as Candida parapsilosis complex includeing Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosis; Candida glabrata complex; and Candida guilliermondii complex. The biological characteristics of each species in the complex are different, and in vitro susceptibilities to antifungal drugs are also different. Candida can grow well on blood agar and Sabouraud dextrose agar, with the optimal temperature of 25 - 37 ℃. Candida albicans is round or oval and 4 - 6 μm in diameter, and reproduces by budding, producing blastospores. Most blastospores do not separate from the metrocyte after extension, forming pseudohyphae, but hyphae can also be seen. Candida glabrata does not form hyphae. Candida albicans grows like yeast in Sabouraud dextrose agar medium, and can form numerous pseudohyphae and characteristic thick-walled spores in rice extract agar medium. Candida chromogenic culture medium helps to quickly identify Candida albicans, Candida tropicalis, Candida glabrata, and Candida krusei in clinical practice.
Clinical manifestations
Candidiasis can be clinically divided into two types, which are also two stages in the course of the disease.
Bronchial candidiasis is characterized by paroxysmal irritating cough, foamy and occasionally bloody expectoration followed by thick expectoration, asthma, tachypnea, fatigue, and diaphoresis, mostly without fever. X-ray only shows thickened lung markings in the middle and lower fields of both lungs.
Pulmonary candidiasis is manifested by chills, high fever, white foamy expectoration with a fermented smell, and sometimes hemoptysis. The clinical manifestations resemble those of acute bacterial pneumonia. Chest x-ray shows increased lung markings in the lower lungs; linear opacities; variously sized, variously shaped, scattered, nodular opacities resembling bronchopneumonia; massive, fused, homogeneous infiltration extending from the hilum to the periphery and forming cavities. Bilateral or multilobar lesions are common, but the apex of the lung is less involved. Occasionally, pleurisy may occur.
Diagnosis
Diagnosis of pulmonary candidiasis requires two microscopic examinations of qualified sputum or bronchial secretion specimens showing positive pseudohyphae or hyphae and bacterial growth in the two cultures showing the same Candida species (except for hematogenous dissemination). In addition, the serum 1,3-β-D-glucan antigen test reveals two consecutive positive results. However, definite diagnosis still requires histopathological evidence.
Treatment
After the elimination of the inducement, the condition of mild patients can often gradually improve. In severe patients, antifungal drugs should be used promptly. Fluconazole, itraconazole, voriconazole, and posaconazole are all effective. The treatment regimen is fluconazole 200 mg a day, with doubled dose for the first administration. In severe patients, 400 mg/d or 6 - 12 mg/(kg.d) can be given. Amphotericin B 0.5 - 1.0 mg/(kg.d) can also be used in severe patients, but the toxicity is greater. Echinocandin antifungal drugs such as caspofungin and micafungin are also effective against Candida albicans. Clinically, they should be selected based on the antifungal susceptibility testing.