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International external quality assessment programme for the molecular detection of Legionella pneumophila in respiratory samples: results from 2006 and 2007

Abstract number: P1982

De Mendonça R., MacKay W.G., Wallace P.S., Rottiers S., Crevecoeur S., Struelens M.J., van Loon A.M.

Objectives: To assess the diagnostic proficiency of laboratories performing nucleic acid amplification technologies for the detection of Legionella pneumophila in clinical specimens.

Methods: The 2006 EQA panel consisted of 12 bronchoalveolar lavage (BAL) or physiological saline solution samples, including eight samples spiked with L. pneumophila sg 1 or sg 6, two samples spiked with Legionella micdadei and two negative samples. The 2007 EQA panel consisted of 10 BAL or transport medium (Dulbecco's modified Eagle's medium and 10% foetal calf serum) samples including seven samples spiked with L. pneumophila sg1 or sg6, one with L. micdadei and two negatives. A scoring system was applied to compare performance: two points for a correct result and zero points for an incorrect result. A maximum score of 24 points was attainable in 2006 and 20 points in 2007.

Results: In 2006 a total of 58 datasets were returned from 51 respondents in 16 countries. The overall mean performance score was 17/24. Three percent (2/58), 14% (8/58) and 84% (49/58) of datasets exceeded 90%, 80% and 60% of the maximum score (24 points). There were 14 (12%) false positives reported for the two samples containing L. micdadei. The rate of false positives on the two true negative samples was 3% (3/116). In 2007, 65 datasets were submitted by 60 respondents in 21 countries. The overall mean performance score was 16/20. Twenty percent (13/65), 52% (34/65) and 89% (58/65) of datasets exceeded 90%, 80% and 60% of the maximum score (20 points). There were 19 (29%) false positives reported for the sample containing L. micdadei. The rate of false positives on the two true negative samples was 4% (5/130). A performance comparison between BAL and transport medium suggested that sample matrix may have influenced the results.

Conclusion: The overall performance improved from 2006 to 2007. However the percentage of false positives on true negative and specificity samples (L. micdadei) indicated that improvements are still needed in the detection of L. pneumophila by molecular methods.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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