Results from the WHO GSS EQAS 2003
-The External Quality Assurance System of the WHO Global Salmonella Surveillance and Laboratory Support Project
Seyfarth AM, Lo Fo Wong DMA, Aarestrup FM and Wegener HC.
An international external quality assurance program on serotyping and antimicrobial susceptibility testing of eight Salmonella enterica strains is performed yearly to enhance the capacity of national and regional reference laboratories in WHO Global Salm-Surv. In 2003, a total of 152 laboratories from 78 countries participated. For testing of Salmonella strains, 81 % of the serotypings and 95 % of the susceptibility tests performed were correct. Quality control (QC) of susceptibility testing was performed with E. coli ATCC 25922 by 93 % of the laboratories. For 45 % of the laboratories, one or more of the QC results were outside the QC ranges given by the CLSI, indicating inadequate
standardization of the methods used and a further need for internal QC and for taking part in quality assurance programs.
In 2003, identification of two thermophilic Campylobacter strains to species level and typing of one blinded bacterial strain, E. coli serotype O157, was included. For Campylobacter, a total of 97 laboratories participated and 85 % of the identifications were correct. For the blinded strain, a total of 115 laboratories participated and 99 % made correct species identification. Only four laboratories performed further typing on the strain, in all cases correct serotype.
In order to identify the barriers for serotyping, the level of difficulty in Salmonella serotyping was considerably higher in 2003 than in previous years. Number one barrier for serotyping was identi-fied as lack of antisera. Misinterpretation of the Kaufmann-White serotyping scheme and of Salmonella taxonomy also played a role. The proportion of incorrect results in serotyping indicates a further need for the training provided by WHO GSS, and a further need for facilitating the availability of high-quality Salmonella antisera at low costs.