The investigation of 76 urines from patients with culture confirmed
urinary tract infections indicates a high specificity of the lateral flow
tests. The ImmuView® assay had 100% specificity for L. pneumophila
and 99% for S. pneumoniae, which is slightly less than the BinaxNOW®
kits which showed 100% specificity for both bacteria. This difference is
not statistically significant. The result indicates that non-specific binding is not an issue, even on un-boiled samples, but further investigation
is needed.
The main method for the diagnosis of Legionnaires' disease in
Europe is urinary antigen tests (Joseph et al., 2010). This may contribute
to an underestimation of the actual number of cases, since the urinary
antigen tests primarily identify serogroup 1 cases. In Denmark, only
approximately 60% of the culture-confirmed cases are caused by
serogroup 1 infection, and more than 20% are due to serogroup 3,
followed by few cases of other serogroups (Kjelsø and Uldum, 2014).
We tested 50 samples fromcaseswith other serogroups than serogroup
1, but were only able to identify 13 of them using the ImmuView® kit,
and just one using the BinaxNOW® and 6 using the Binax® EIA kit.
Even though the ImmuView® assay did find a few of these samples
and performed better than the BinaxNOW® and Binax® EIA, this
emphasizes the importance of using other methods than the urinary
antigen tests, leaving PCR combined with culture as the gold standard
in order to be able to identify cases caused by other serogroups.
We are aware that the panel of Legionnaires' disease cases does not
reflect what is seen in a normal diagnostic setting, since the proportion
ofMAb 3/1 negative cases are vastly overrepresented even for Denmark.
The low sensitivity for Binax EIA for this group is unexpected and probably
not a general problem, but this must be investigated further.