WHO Global Salm-Surv external quality assurance system for serotyping of Salmonella isolates from 2000 to 2007.

An international external quality assurance system (EQAS) for the serotyping of Salmonella species was initiated in 2000 by WHO Global Salm-Surv to enhance the capacity of national reference laboratories to obtain reliable data for surveillance purposes worldwide. Seven EQAS iterations were conducted between 2000 and 2007. In each iteration, participating laboratories submitted serotyping results for eight Salmonella isolates. A total of 249 laboratories in 96 countries participated in at least one EQAS iteration. A total of 756 reports were received from the participating laboratories during the seven EQAS iterations. Cumulatively, 76% of participating laboratories submitted data for all eight strains, and 82% of strains were correctly serotyped. In each iteration, 84% to 96% of the laboratories correctly serotyped the Salmonella enterica serovar Enteritidis isolate that was included as an internal quality control strain. Regional differences in performance were observed, with laboratories in Central Asia and the Middle East performing less well overall than those in other regions. Errors that resulted in incorrect serovar identification were typically caused by difficulties in the detection of the phase two flagellar antigen or in differentiation within antigen complexes; some of these errors are likely related to the quality of the antisera available. The results from the WHO Global Salm-Surv EQAS, the largest of its kind in the world, show that most laboratories worldwide are capable of correctly serotyping Salmonella species. However, this study also indicates a continuing need for improvement. Future training efforts should be aimed at enhancing the ability to detect the phase two flagellar antigen and at disseminating information on where to purchase high-quality antisera.

Human health impact of Salmonella contamination in imported soybean products: a semiquantitative risk assessment.

The objectives of our study were to estimate the number of reported cases of human salmonellosis in Denmark that can be attributed to the occurrence of Salmonella in soy-based animal feed and to assess whether certain serotypes can be considered of less importance to human health. The assessment was based on a comparison of Salmonella serotypes isolated from feedstuffs, swine, cattle, and humans, primarily collected through the Danish Salmonella surveillance programs, supplemented with international data sources. The results are presented in three different forms: a qualitative assessment of all serotypes isolated from animal feed and/or food-producing animals based on their detection in humans; a semiquantitative ranking of serotypes by the apparent differences in their public health impact; and an estimate of the number of reported cases of human salmonellosis that can be attributed to the occurrence of Salmonella in soy-based animal feed. Salmonella isolates included in this study belonged to 91 distinct serotypes. Of the 82 serotypes found in both production animals and humans, 45 were also found in feed. In the period from 1999 to 2003, 14.4% of reported human infections were caused by serotypes also isolated from animal feed. Based on a modified version of a previously published risk model, we estimated that up to 1.7% of the total number of reported human cases and 2.1% of domestically acquired infections in the period 1999-2003 could be attributed to feedborne serotypes acquired through the consumption of Danish pork and beef. We concluded that more than 90% of serotypes have the potential, if they occur in feedstuffs, for infecting humans via production animals or foods of animal origin.