2012 Voluntary Non-O157:H7 STEC Proficiency Testing Study

Introduction: For U.S. clinical laboratories, proficiency testing (PT) has evolved into an essential component of quality assurance programs.  These laboratories are regulated by CLIA 1988, which mandates participation in PT. Food laboratories may soon be subject to similar requirements with passage of the Food Safety Modernization Act, which may require laboratory accreditation for foods regulated by the FDA.  On September 14, 2011, the USDA announced that the following “Big 6” non-O157:H7 Shiga Toxin-producing Escherichia coli’s (STECs) are considered adulterants: O26, O45, O103, O111, O121, and O145.  Mandatory testing of beef trim for these STECs began June 4, 2012. 

Purpose: This pilot PT study includes data from three test events in 2012, where participants volunteered to submit results for detection and identification of an unknown STEC. Our objective was to assess whether laboratories have the ability to identify the presence of one of the above STECs.

Methods: False (-) rates for STECs were recorded from 101 cumulative proficiency testing results submitted in three test events in the year 2012. No false (+) data was collected as participants were informed that an STEC was present in the sample. 

Results: Performance accuracy for STECs appears problematic with results indicating a false negative/misidentification rate of 6%. In addition, a significant number of results (21%) indicated that an STEC was present, but participants were unable to identify the strain.

Significance: As laboratories begin to routinely test for STECs, and as laboratory test methodologies improve, it is anticipated that the ability of laboratories to correctly identify STECs will increase. However, this false (-) rate is similar to the 14 year API average of false (-) E. coli O157:H7, 6.6%.