53 A Single Center’s Experience Replacing Culture with a Multiplex RT-PCR Assay for the Detection of Legionella species in Lower Respiratory Specimens

Background Legionella species are environmental bacteria, which can cause community acquired pneumonia. This study describes one laboratory’s experience replacing Legionella culture with a laboratory developed multiplex RT-PCR assay to detect Legionella spp. (srrA), L. pneumophila (mip), and L. pneumophila serogroup 1 (wzm) in lower respiratory specimens. Methods Two, one-year retrospective analyses were performed to assess Legionella detection rate and variety of species detected using culture (pre-implementation) and PCR (post-implementation). During the post-implementation period, orthogonal testing (reflex culture or public health PCR analysis) was used to assess the specificity of laboratory PCR results. A chi-square test was used to assess the statistical significance of the difference of detection rates between the pre-implementation and post-implementation groups. Results During the pre-implementation period, 765 Legionella cultures were performed of which Legionella spp. was detected from six patients’ specimens (6/765; 0.78%). All cultured isolates were identified as L. pneumophila (6/6; 100%). During the post-implementation period, 3,490 RT-PCR tests were performed, and 23 samples had Legionella spp. detected (23/3,490; 0.70%). Twenty of the 23 samples were from unique patients and included Legionella species but not L. pneumophila (4/20; 20%), L. pneumophila not serogroup 1 (8/20; 40%), L. pneumophila serogroup 1 (6/20; 30%), and Legionella species, unable to specify (2/20; 10%). Remnant samples were further assessed on 14 of these post-implementation specimens using culture within the local laboratory and PCR testing at a public health laboratory. More than half (8/14; 57%) of the reflex cultures recovered Legionella spp., and the identified species were concordant with PCR findings (8/8; 100%) including L. pneumophila (5/5; 100%) and L. species, not L. pneumophila (3/3; 100%), which included L. maceachernii, L. micdadei, and L. feeleii. All PCR testing performed by public health was concordant (14/14; 100%). There was no significant difference between the positivity rate of culture in the pre-implementation phase and the positivity rate of PCR in the post-implementation phase (p = .44). Conclusion Replacing Legionella culture with Legionella species multiplex real-time PCR had no significant effect on test positivity. Legionella species other than L. pneumophila were only detected in the post-implementation period. More than half of cases with detected Legionella were attributed to taxa other than L. pneumophila serogroup 1. Positive PCR results reliably were confirmed with culture and PCR performed at a public health laboratory.