Trends in Foodborne Illness in the United States; 1996-2013

Introduction: Current statistical methods for evaluating national foodborne illness surveillance data over time make pair-wise comparisons between the most recent surveillance year and one or more baseline periods. This avoids the problem of specifying the model form for trend (e.g., linear, exponential, polynomial) but cannot distinguish trends in foodborne illness from year-to-year variability.

Purpose: The analysis examines trends in U.S. foodborne illness without specifying a model form for trend.

Methods: The analysis considers FoodNet (Foodborne Diseases Active Surveillance Network) cases and population data for 1996-2013 for Campylobacter, Listeria, Salmonella, Shigella, STEC O157, Vibrio, and Yersinia. To control for the addition of states to the FoodNet surveillance system over time, available data from the original five states (CA, CT, GA, MN, OR) for 1996-2012 are analyzed separately. The trend analysis uses B-splines, a flexible, semi-parametric regression method.

Results: Campylobacter, Listeria, STEC O157, and Yersinia exhibit early decreases in reported incidence followed by no trend. Shigella steadily decreased in reported incidence over time. Salmonella and Vibrio exhibit increasing trends in reported incidence. The results are insensitive to whether the data from all states or the original five states are considered.

Significance: The findings indicate a lack of evidence for continuous reduction in foodborne illnesses in the U.S. during 1996-2013.