Diagnosis of Respiratory Tract Infection and the Use of the Laboratory

Lower respiratory tract infections continue to be among the most commonillnesses requiring medical attention with considerable morbidity and morality. Clinical features, includingunderlying conditions, presenting signs and symptoms, basic laboratory investigations and chestroentgenograms, are not sufficiently precise to infer an etiological agent. These investigations do permit anassessment of severity of illness and can assist in stratification of patients into high risk groups. Properlyperformed and interpreted Gram stain of sputum is still useful in the initial assessment of these patients,but sputum cultures are less helpful. Blood cultures should be drawn in patients ill enough to requirehospitalization, but the yield is low, Pneumococcal antigen testing and serological studies do not add tothe routine management of patients with pneumonia. In patients with nosocomial pneumonia, the diagnosiswill be established by a synthesis of clinical, roentgenographic and simple laboratory results such assputum analysis and blood culture. Invasive investigations should be reserved for critically ill patients