Intech Open Access
Infections in the respiratory tract are very common but majority involve the upper respiratory system. Pneumonia is usually caused by inhalation of infecting organisms or the same may reach the lung via bloodstream. Pulmonary pathogens can cause tissue damage by a direct invasive cytolytic process or by releasing toxins (endotoxins and/or exotoxins). Acute inflammation may lead to complete resolution, destructive pneumonia with abscess formation, healing by fibrosis or chronic inflammation. Various infective agents causing pneumonia include viruses, bacteria, Mycobacteria, fungi, Chlamydiae, Mycoplasmas or parasites. The diagnosis of various pulmonary infections is initially based on radiological evaluation depending upon chest X-ray, CT scan or MRI (magnetic resonance imaging). Cytological techniques used for detection of pulmonary infections include sputum examination, bronchial washing & brushing, bronchoalveolar lavage, transbronchial/ transthoracic fine needle aspiration (FNA) and EUS (endoscopic ultrasonography) guided FNA. Transbronchial lung biopsies are performed for histopathological detection of various infections and for histological evidence of invasion. Tissue can be obtained by these techniques for culture or other molecular diagnostic techniques such as polymerase chain reaction (PCR). Special stain most commonly used for bacteria is Gram’s stain and for fungi are Gomori's methenamine silver (GMS), Gridley's fungus (GF), and periodic acid-Schiff (PAS) stains.