[The radiology of opportunistic pneumonias. I: Epidemiological, laboratory and clinical background]

In the guidelines of the German Society of Pneumology on diagnosis and therapy of opportunistic pneumonias, chest x-ray is listed as the basic diagnostic method in congenital and acquired immunodepression. In case of discrepancy between radiographic and the clinical findings or in cases of bilateral infiltrates, infection refractory to therapy or a difficult course in patients requiring artificial ventilation, a CT, or if necessary, ultrasound or MRI should be carried out. Cross-sectional imaging allows more precise assessment of the radiological pattern, estimation of the degree of severity (number of infiltrated segments) and detection of complications (pleural effusion, empyema, thorax wall infiltration). Clinical and laboratory parameters, bacteriological and serological examinations as well as information on the underlying immunocompromising factors must be taken into account in the differential diagnosis. The radiographic finding is an important diagnostic parameter which is used in the determination of the degree of severity of the pneumonia. The pattern of findings is one of rationales for the use of antibiotic therapy. In the first part of this contribution the epidemiological, laboratory and clinical background of the diagnosis of opportunistic pneumonias is discussed.