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Legionellosis (Legionella pneumophila) (Legionnaires’ Disease)
1996 Case Definition
Clinical description
Legionellosis is associated with two clinically and
epidemiologically distinct illnesses: Legionnaires disease, which
is characterized by fever, myalgia, cough, pneumonia, and Pontiac
fever, a milder illness without pneumonia.
Laboratory criteria for diagnosis
- Isolation of Legionella from respiratory
secretions, lung tissue, pleural fluid, or other normally sterile
fluids, or
- Demonstration of a fourfold or greater rise
in the reciprocal immunofluorescence antibody (IFA) titer to
greater than or equal to 128 against Legionella pneumophila serogroup
1 between paired acute- and convalescent-phase serum specimens,
or
- Detection of L. pneumophila serogroup
1 in respiratory secretions, lung tissue, or pleural fluid
by direct fluorescent antibody testing, or
- Demonstration of L. pneumophila serogroup
1 antigens in urine by radioimmunoassay or enzyme-linked immunosorbent
assay
Case classification
Confirmed: a clinically
compatible case that is laboratory confirmed
Comment
The previously used category of "probable
case," which was based on a single IFA titer, lacks specificity
for surveillance and is no longer used.
See also:
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