284
Legionellae sampling and detection
Culture from clinical or environmental samples is a preferred method
for
Legionella
detection. Molecular methods of detection such as PCR may
also be useful to screen samples, but do not discriminate between live and
dead organisms and are usually not specific enough to subtype legionellae
to the level needed for investigation of cases of disease. Clinical cases of
Legionnaires’ disease may be diagnosed by a urinary antigen test, but it is
only specific for Lp1 and does not yield any other subtyping information
(45-47). Testing for
Legionella
in environmental samplesmay be undertaken
to establish the source of an outbreak of Legionnaires’ disease, to determine
the efficacy of a disinfection program, or to evaluate the potential of a
device to transmit the disease. Routine environmental sampling can also
be beneficial in institutions housing persons at extremely high risk for
acquiring Legionnaires’ disease, such as solid organ transplant wards,
with the understanding that the objective is no detectable legionellae in
the water system (48). However, recommendations concerning the routine
culturing of environmental samples in the absence of documented cases
of legionellosis represent an area of considerable controversy for a variety
of reasons. Detection of legionellae in an environmental source is not
necessarily evidence of the potential for disease. There are conflicting data
informing diverse sampling methodologies and interpretation of results
(49). In addition, the type of sample collected, transport procedures, and
variable laboratory sample handling processes can have a large effect on
both the number of positive sites identified and the number of legionellae
recovered (50-54). In fact variability approaching 3 logs is not uncommon
in even “standardized” samples spiked with live bacteria or reconstituted
from lyophilized stock for proficiency testing purposes (55, 56).
