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Role of Reference Laboratories in Detecting Laboratory Contamination
Niall De LappeNational Salmonella Reference Laboratory,Galway, Ireland
Introduction
Why does it occur? Positive Control Other Positive Isolates
Problem Pseudo-Outbreaks Potential Cost to Food Industry
Scale of Problem
M.tuberculosis 1.8-3.5% misdiagnosis
Estimating causes and Rate of laboratory contamination Sinnika Pelkolen
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)
6
9
2
7
111
4
2
111
2
2
2
11
2 10
2
4
6
8
10
12
Y2001 Y2002 Y2003 Y2004 Y2005 Y2006 Y2007
Incidents of Laboratory Contamination
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
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
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)
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
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)
PFGEBlnI XbaI
Variable Number Tandem Repeats
No. Date Lab Source PFGE VNTR03-0407 2003 d Human Indistinguishable
07-0200 2007 f Pork 2 band difference
07-0201 2007 f Unknown Indistinguishable
07-0204 2007 f Unknown Indistinguishable
05-0802 2005 e Human Indistinguishable
07-0028 2007 f Pork Indistinguishable
07-0060 2007 f Pork Indistinguishable
05-0900 2005 C Milk Powder
Indistinguishable
05-0902 2005 C Swine Indistinguishable
07-0146 2007 C Milk Powder
Indistinguishable
07-0237 2007 C Swine Indistinguishable
07-0147 2007 f Swine Indistinguishable
04-03-10-02-02
04-03-10-02-02
04-03-11-02-02
04-03-11-02-02
04-03-11-02-02
04-04-11-00-02
04-04-11-00-02
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
Results
Lessons
Positive Control S.Nottingham Value of Subtyping strains routinelyValue of different subtyping methodsSensitive Products
Store Product for Retesting Test in different area/time than other
samples
Acknowledgements
NSRL staff EnterNet All for listening