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