Evaluation of a public health Salmonella surveillance system in King County, Washington

Abstract

Objectives: Salmonella infection is the most common cause of foodborne bacterial outbreaks and deaths in the United States. The effectiveness of Salmonella surveillance for detecting outbreaks depends on timeliness of reporting. We evaluated the public health Salmonella surveillance system in King County, Washington, during an outbreak and at baseline.

Methods: We assessed the timeliness of the Salmonella surveillance system in King County using the Public Health-Seattle & King County Laboratory (County PHL) database from 1998 to 1999. We determined median days for key steps involved in the Salmonella identification and reporting process and the percentage of suspected Salmonella isolates confirmed. Time intervals for key steps during a Salmonella outbreak were compared to baseline surveillance.

Results: Of the 652 suspected Salmonella isolates sent to the County PHL from 22 clinical laboratories, 617 (94.6%) were confirmed as Salmonella. Salmonella confirmation rates improved from 1998 to 1999, and 41% of the submitting laboratories, contributing 32.4% of the isolates, had 100% confirmation rates for both years. The median total identification time during the outbreak did not differ significantly from baseline (13 days vs 17 days). The time interval for serotyping contributed most to the total identification time.

Conclusions: King County's Salmonella surveillance system requires more than 2 weeks to confirm and report serotype results for Salmonella isolates. Variation in total identification time depends on serotyping time. A more detailed study of other surveillance systems may identify approaches to decrease total identification time.