Proportion of illness acquired by foodborne transmission for nine enteric pathogens in Australia: An expert elicitation

Background: Estimates of the burden of illness acquired from food inform public health policy and prioritize interventions. A key component of such estimates is the proportion of illnesses that are acquired by foodborne transmission. In view of the shortage of requisite data, these proportions are commonly obtained through a process known as expert elicitation. We report findings from an elicitation process used to assess the importance of the foodborne transmission route for nine pathogens in Australia, circa 2010. Materials and Methods: Eleven experts were asked to estimate the proportion of illness acquired by five transmission routes: food, environmental, water, person, and zoonotic, together with a 90% certainty interval for foodborne transmission. Foodborne estimates and intervals from each expert were combined using both modified triangular and Program Evaluation and Review Technique (PERT) distributions, in @Risk version 6, to generate final distributions from which median estimates and 95% Credible Intervals (CrI) were calculated. Results: Shiga toxin-producing Escherichia coli (STEC) was the only pathogen believed to have an important zoonotic transmission route, while norovirus, hepatitis A virus, non-STEC pathogenic E. coli, and Shigella spp. were all thought to be primarily spread from person to person. Foodborne transmission was the main route for Clostridium perfringens (98%, CrI: 84-100), Listeria monocytogenes (98%, CrI: 86-100), nontyphoidal Salmonella spp. (72%, CrI: 50-87), and Campylobacter spp. (77%, CrI: 60-90). Foodborne estimates using the modified triangular distribution had wider CrI than these calculated using the PERT distribution. Conclusions: Foodborne proportions for most pathogens in this study were the same or lower than those estimated circa 2000 in Australia, with the greatest decline for non-STEC pathogenic E. coli. Inclusion of certainty intervals from experts helps to quantify the precision of foodborne proportions. A decline in estimates of the foodborne proportion for common pathogens will influence final estimates of the burden of illness acquired from food.