Prognosis

Most patients survive with timely treatment and return to their normal baseline level of health. Clinical response to treatment is usually prompt, within 2-5 days.[67]

Persistent symptoms and impaired quality-of-life measures that persist for >28 days are likely to be due to age and comorbidity rather than the pneumonia itself.[80] A study of survivors of Legionnaires' disease found that symptoms and impaired quality-of-life measures may persist for several years.[81]

Legionnaires’ disease has a mortality rate of 8% to 12% in most people (if given appropriate antibiotic treatment), but this may be higher in older adults or people who have preexisting medical conditions, smoke, have nosocomial cases, or have a delay in diagnosis and treatment of their disease.[4][82]​​​ The average case-fatality rate is 9% in Europe and 7% in the US.[6][7]​​​​

A complication such as lung abscess may require surgery and worsens prognosis significantly.

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