290
Legionellae samplinganddetection
Culture from clinical or environmental samples is a preferredmethod
for
Legionella
detection.Molecularmethods of detection such asPCRmay
alsobe useful to screen samples, but donot discriminate between live and
deadorganisms and are usuallynot specific enough to subtype legionellae
to the level needed for investigation of cases of disease. Clinical cases of
Legionnaires’ diseasemay be diagnosed by a urinary antigen test, but it is
only specific for Lp1 and does not yield any other subtyping information
(45-47).Testingfor
Legionella
inenvironmentalsamplesmaybeundertaken
toestablish the sourceof anoutbreakofLegionnaires’disease, todetermine
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
thewater 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 conflictingdata
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 testingpurposes (55, 56).
