Effect of Salmonella Cluster Detection and Investigation Methods on Outbreak Reporting in the United States 2013-2017

Cluster detection and outbreak investigation practices and resources vary across states. There is a lack of evidence to evaluate the effectiveness of Salmonella cluster detection and investigation practices on outbreak detection and reporting by states. We conducted an online survey of all 50 U.S. state health departments (HD) in 2015 to assess how pulsed-field gel electrophoresis (PFGE) cluster detection and outbreak investigation practices and resources at the state affected reporting single-state Salmonella outbreaks to CDC's Foodborne Disease Outbreak Surveillance System (FDOSS) from 2013-2017. Increased rates of Salmonella outbreak reporting were observed for states that used a standard hypothesis generating questionnaire (HGQ) for conducting hypothesis generating interviews (HGI) (155% increase), conducted routine HGI for all cases (85% increase), and used a standard PFGE cluster definition (40% increase) compared to states that did not use these practices. Multivariable regression models demonstrated that participation in the Foodborne Diseases Center for Outbreak Response Effectiveness (FoodCORE) or OutbreakNet Enhanced (OBNE) and per capita funding through Epidemiology and Laboratory Capacity (ELC) grants explained more of the variability in outbreak reporting than individual surveillance practices. Results suggest that the combination of practices promoted by FoodCORE and OBNE enhance the potential effectiveness of the individual practices used in isolation. While PFGE is no longer the standard method for subtyping, these findings demonstrate how surveillance activities relate to outbreak reporting and provide a framework for evaluating the impact of current surveillance practices. With the shift from PFGE to whole genome sequencing (WGS), ongoing evaluation of surveillance practices at state and local levels will be critical to maintaining the evidence base for effective surveillance and reducing the public health burden of Salmonella infections.