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Role of Reference Laboratories in Detecting Laboratory Contamination

Role of Reference Laboratories in Detecting Laboratory Contamination. Niall De Lappe National Salmonella Reference Laboratory, Galway, Ireland. Introduction. Why does it occur? Positive Control Other Positive Isolates Problem Pseudo-Outbreaks Potential Cost to Food Industry.

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Role of Reference Laboratories in Detecting Laboratory Contamination

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  1. Role of Reference Laboratories in Detecting Laboratory Contamination Niall De Lappe National Salmonella Reference Laboratory, Galway, Ireland

  2. Introduction • Why does it occur? • Positive Control • Other Positive Isolates • Problem • Pseudo-Outbreaks • Potential Cost to Food Industry

  3. Scale of Problem • M.tuberculosis • 1.8-3.5% misdiagnosis • Estimating causes and Rate of laboratory contamination • Sinnika Pelkolen

  4. Incidence of False Positive Salmonella Isolations • 2001 1 (n = 6) • 2002 2 (n =11) • 2003 3 (n = 9) • 2004 5 (n = 9) • 2005 6 (n = 9) • 2006 1 (n = 2) • 2007 1 (n = 1)

  5. Lab A • S.Typhimurium DT132 • Oct 2003 Beef (n=1) • Nov 2003 Beef (n=4) & Drain swab (n=1) • Dec 2003 Pork (n=1) • Jan 2004 Beef (n=1) • Feb 2004 Pork (n=1) and Powder (n=1) • Apr 2004 Beef (n=1) • Sent Positive Control • S.Typhimurium DT132

  6. Lab B • Clinical case • 78 y.o. patient hospitalised > 30 days • Developed diarrhoea • Isolated salmonella from selenite broth • Salmonella from other patient same day • Primary plate • Both typed as Enteritidis PT1, Na resistant • Considered cross-contaminant

  7. Lab C • Isolate from Milk Powder • S.Typhimurium, Phage Type Untypable, ASSuT • Asked to send all group B isolates from 2007 • S.Typhimurium (n = 17) • S.Derby (n = 26) • S.Reading (n = 4) • S.Bredeney (n = 2) • S.Manhattan (n = 1) • S.Agama (n = 1)

  8. Phage Typing and Antibiograms • Index Isolate Untypable/ ASSuT • DT104 / ACSSuT (n = 4) • DT193 / ACSuTm (n = 3) /ACSSuTTm (n = 1) • DT12 / A (n = 1) • DT2 / T (n = 1) • DT120 / none (n = 1) • U302 / ACSSuTTm (n = 1) • RDNC / T (n = 2) • Untypable / SSu (n = 1) / ASSuT(n = 1)* from swine

  9. S.Typhimurium, ASSuT, Untypable • Literature Review • Associated with Swine • NSRL Databases • Human isolates (n = 2) • Swine (n = 6) • Unknown (n = 2) • Milk Powder (n = 2)

  10. PFGE BlnI XbaI

  11. Variable Number Tandem Repeats

  12. Results 05-02-07-14-02 05-02-07-00-02 04-03-07-02-02 04-04-16-21-02 04-03-10-02-02 04-03-10-02-02 04-03-10-02-02 04-04-11-00-02 04-04-11-00-02 04-03-11-02-02 04-03-11-02-02 04-03-11-02-02

  13. Lessons Positive Control S.Nottingham Value of Subtyping strains routinely Value of different subtyping methods Sensitive Products • Store Product for Retesting • Test in different area/time than other samples

  14. Acknowledgements • NSRL staff • EnterNet • All for listening

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