Study and control of bacteriological key points in Salmonella surveillance

Objective To study and control the technical key points in Salmonella isolation, and evaluate the surveillance results. Methods Stock strains, anal swabs and food enrichment samples were used to compare the sensitivity of the separate combinations of 5 Salmonella-selective plates with 3 selective enrichment broths for detection of Salmonella. The combination of selenite brilliant green (SBG) enrichment with xylose lysine deoxycholate (XLD) agar and CHROMagarTM Salmonella (CAS) chromogenic medium was used as Method 1 for global salmonella surveillance (GSS) in the laboratories of four centers for disease control and prevention (CDCs) in Shanghai. The SBG-XLD combination as Method 2 was employed to parallel the CDC laboratory tests. Results The sensitivity of CAS and XLD was 100.0% and 85.7%, respectively. As for the rectal swabs enriched by SBG, the isolation sensitivity was 94.4% and 89.7% using CAS and XLD, respectively. The positive rate of GSS ranged between 2.6% to 3.8% from 2006 to 2009 with a peak of 5% to 7%. The clinical sensitivity reached 78.7% of the sensitivity of laboratory results with a maximum of 88.9%. Conclusion Effective enrichment is a key point in Salmonella isolation, and strengthening training for laboratory staff and using uniform isolation materials are the one in controlling Salmonella surveillance. Method 1 was applicable for detection of all Salmonella, while Method 2 was suitable for detection of non-typhoid Salmonella. Modular, alternative combinations may balance between efficiency and cost for isolation of strains.