What is the role of direct fluorescent antibody staining of sputum in the diagnosis of Legionnaires disease?

Updated: Mar 11, 2021
  • Author: Chinelo N Animalu, MD, MPH; Chief Editor: Michael Stuart Bronze, MD  more...
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Direct fluorescent antibody staining (DFA) is a rapid test that yields results in 2-4 hours, but it has a lower sensitivity and has fallen out of favor. The specificity of DFA is 96-99% using monoclonal antibody instead of polyclonal antibody.

A positive result depends on finding large numbers of organisms in the specimen; therefore, the sensitivity is increased when samples from the lower respiratory tract are used. DFA results rapidly become negative (in 4-6 d).

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