Exposure assessment to Salmonella by consumption of informally marketed milk and Gouda cheese in Musanze town, Rwanda

Abstract

This study assesses the exposure to Salmonella by consumption of boiled milk and Gouda cheese in Musanze town, Rwanda. A consumer survey (n = 90) revealed that among milk buyers in milk shops, 40.0% were also buying boiled milk for their families resulting in consumption by 136 consumers, mainly adults aging between 19-29 years (32.3%). Among those interviewed consumers in households, 66.7% were re-boiling the milk and 33.3% were storing it refrigerated before consumption. Gouda cheese is usually sold in supermarkets belonging to the formal market. A cheese portion with a weight of 62.5 g is mainly consumed (80.0 % , n=370), and the weekly consumption frequency is most in practice (38.1%). A probabilistic exposure model was built up by taking into account prevalence data of Salmonella contamination in boiled milk and Gouda cheese in Rwanda, assumed concentration data of Salmonella, information of the milk chain gathered by observation, and collected consumption data and consumer behavior information. Finally, the risk of infection per day and per year were calculated for different categories of consumers. It appears that even though Salmonella is eliminated by milk boiling, the risk of infection still persists due to post-contamination in the milk shops (8.4% of consumers infected per year ), but is decreased by additional boiling in households to 4.9% (children) and 4.6% (adults) per year . For cheese consumption, the risk of infection was lowered by multiple food safety interventions for cheese producers such as trainings on food hygiene and provision of modern equipments improving thus the situation from before to after 2012 by 30.0%% per year in case of adults. Those calculations demonstrate clearly that the additional efforts to reduce the occurrence of Salmonella in the Rwandan dairy chain will benefit the Rwandan population and decrease the burden of food borne disease. Keywords: Salmonella; exposure assessment; milk; dairy.