The clinical picture and radiologic findings in a sporadic case of Legionnaires' disease are not specific. In the setting of an outbreak, particularly in summer, the diagnosis of Legionnaires' disease should be considered in patients with segmental, lobar, or interstitial pneumonia in which the etiologic agent is not evident on Gram's stains of sputum or tracheal secretions. A mild case may resemble Mycoplasma pneumonia or other types of atypical pneumonia. Treatment On in vitro susceptibility testing, L. pneumophila is susceptible to a variety of antimicrobial agents, including erythromycin and the new macrolides, tetracycline, rifampin, and the fluoroquinolones. Occasionally, patients may experience a relapse if erythromycin is discontinued shortly after there has been a clinical response.
Recovery occurs during a second, more prolonged course of erythromycin.
A combination of erythromycin and rifampin should be considered in patients who fail to respond to erythromycin alone and in immunologically impaired patients with overwhelming disease. Clarithromycin, azithromycin, ciprofloxacin, and ofloxacin are active in vitro, but clinical experience with these drugs is limited. Clindamycin appeared to be effective in an immunocompromised patient with a lung abscess caused by L. pneumophila . Since 1943, unusual, fastidious rickettsia-like organisms have been identified as causes of isolated cases of pneumonia. Long considered medical curiosities, these organisms were named after their discoverers or the patients from whom they were isolated.