Diagnostic problems in lower respiratory tract infections.

The main problems of diagnosis in lower respiratory tract infection are the differentiation of infection from colonization or contamination, and the isolation of a reliable and true pathogen. The clinical findings and differentiation of patients into those with pneumonia or infective exacerbations of chronic bronchitis should provide a definitive early diagnosis. Expectorated sputum may be unreliable in pneumonia, because of contamination by oropharyngeal flora. Although blood cultures may be negative, they provide a precise diagnosis and should be obtained in all pneumonias admitted to hospital. Other more invasive procedures are transtracheal needle aspiration, fibrebronchoscopic techniques including protected specimen brush and bronchoalveolar lavage with quantitative culturing and cytological analysis, transthoracic needle aspiration, thoracoscopy--guided biopsy and open lung biopsy. Any invasive procedure in a severely ill patient should be carefully directed weighing the risks as well as the benefits, whilst taking the underlying disease and expected survival into consideration.