Chapter 1 : Clinical Features of Legionnaires’ Disease: A Selective Review

Abstract:

Legionnaires’ disease was thought to be an atypical and easily recognized form of pneumonia for several years after the 1976 Philadelphia epidemic. Astute clinicians began to question the characterization of the illness as clinically unique, and in a seminal prospective study of community-acquired and nosocomial pneumonia, researchers showed that Legionnaire's disease could not be distinguished on presentation from non-Legionnaires’ disease cases of pneumonia. This study was followed by several others showing that neither community-acquired nor nosocomial Legionnaire's disease could be accurately distinguished on presentation from other common pneumonias on clinical, laboratory, and roentgenographic grounds. Each study found one or two differences between Legionnaire's disease and other pneumonias, often differing from one study to another. Another recent approach that has been taken to detect Legionnaires’ disease is the analysis of blood acute phase reactant levels. Researchers measured blood procalcitonin and neopterin levels in pneumonia patients with and without Legionnaires’ disease, which showed that patients with pneumococcal pneumonia had higher levels of procalcitonin and lower levels of neopterin than did Legionnaires’ disease patients and that procalcitonin levels increased with greater disease severity regardless of diagnosis. Several types of probably noninfectious extrapulmonary disease have also been recognized since the 1976 Legionnaires’ disease epidemic.