Radiological manifestations of Legionella/Legionella-like organisms.

The chest radiograph of Legionellosis has been described in many reports. Although some attempted to describe patterns which are specific for Legionella, in fact, the roentgenographic findings in Legionella infection vary widely and depend largely on when in the course of illness the radiograph is obtained. Certain temporal characteristics, however, can serve to enhance the likelihood of the diagnosis of Legionella pneumonitis. Initial focal infiltrates are most commonly poorly marginated with 10% presenting with concomitant pleural effusion. The infiltrates often spread to contiguous lobes eventually becoming bilateral, with incidence of pleural effusions reaching 35%. This progression often occurs despite appropriate antimicrobial therapy and often in the face of clinical improvement. A similar pattern of progression also occurs in immunocompromised individuals; in addition, a high rate of cavitation and hilar adenopathy is seen in this subset of patients. A prolonged resolution phase of up to 6 months is common with rare development of residual densities. Correlating radiographic features with disease severity and mortality have largely been unsuccessful.