Abnormal radiological findings and a decreased carbon monoxide transfer factor can persist long after the acute phase of Legionella pneumophila pneumonia. 
Pulmonary abnormalities may persist long after the acute phase of legionnaires disease (LD).  In a cohort of 122 survivors of an outbreak of LD, 57% were still experiencing an increased number of symptoms associated with dyspnea at a mean of 16 months after recovery from acute-phase LD.  For 86 of these patients, additional evaluation involving high-resolution computed tomography (HRCT) of the lung revealed pulmonary abnormalities in 21 (24%); abnormal HRCT findings generally presented as discrete and multiple radiodensities.  Residual pulmonary abnormalities were associated with a mean reduction of 20% in the gas transport capacity of the lung.  This latter sign could not be used to explain the increased symptoms of dyspnea reported by patients.  Receipt of mechanical ventilation during the acute phase of LD, delayed initiation of adequate antibiotic therapy, and chronic obstructive pulmonary disease were identified as risk factors for the persistence of lung abnormalities.