Legionellosis (Legionella pneumophila) (Legionnaires’ Disease)

1995 Case Definition

The 1995 case definition appearing on this page was previously published in the 1990 MMWR Recommendations and Reports titled Case Definitions for Public Health Surveillance [MMWR 1990;39(RR13)] (available at http://www.cdc.gov/mmwr/preview/mmwrhtml/00025629.htm). Thus, the 1990 and 1995 versions of the case definition are identical.

Clinical description

An illness with acute onset, commonly characterized by fever, cough, and pneumonia that is confirmed by chest radiograph. Encephalopathy and diarrhea may also be included.

Laboratory criteria for diagnosis

• Isolation of Legionella from lung tissue, respiratory secretions, pleural fluid, blood, or other normally sterile sites, or
• Demonstration of a fourfold or greater rise in the reciprocal immunofluorescence (IF) antibody titer to greater than or equal to 128 against Legionella pneumophila serogroup 1, or
• Demonstration of L. pneumophila serogroup 1 in lung tissue, respiratory secretions, or pleural fluid by direct fluorescence antibody testing, or
• Demonstration of L. pneumophila serogroup 1 antigens in urine by radioimmunoassay

Case classification

Probable: a clinically compatible illness with demonstration of a reciprocal antibody titer greater than or equal to 256 from a single convalescent-phase serum specimen

Confirmed: a case that is laboratory confirmed

See also:

• 2005 Case Definition
• 1996 Case Definition

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