Role of Reference Laboratories in Detecting Laboratory Contamination Niall De Lappe National...

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