| Sumario: | Background: Listeriosis is a group of disorders caused by the bacterium Listeria
monocytogenes. The organism, which is considered to be recalcitrant to environmental
stress such as freezing, refrigeration, drying and heating to a remarkable extent, is
widely distributed in the environment and is consequently associated with various food
products of both plant and animal origin including unpasteurized or under-pasteurized
fresh cow’s milk. The disease has the highest case-fatality ratio of all food-borne
diseases and it is considered as an emerging food-borne disease globally. In Ghana,
the consumption of unpasteurized daily products is widely practiced in some milk
producing communities. This study, aiming at improving the safety of animal-sourced
foods, assessed the risk of consuming raw or unprocessed milk from the informal
milk markets in Ghana that may be contaminated with Listeria monocytogenes and
determined the best options for mitigating the problem. Methods: Modular Process
Risk Models (MPRM) are a recent framework for quantitative microbial risk assessment.
This identifies key steps and to each assigns one or more basic processes which
can be described mathematically. A MPRM was developed to quantitatively assess
the risk of consuming dairy products from the informal market contaminated with L.
monocytogenes based on three risk inputs: the quantitative diary market chain model,
information on handling of milk, and contamination rates of milk/milk products with L.
monocytogenes in each pathway. Data from participatory rural appraisal and interviews
of stakeholders of informal milk markets were used to model the quantitative diary
market chains and milk handling practices. L. monocytogenes contamination rates
were obtained by laboratory testing of milk samples from the chains. Results: L.
monocytogenes was detected in samples from 42-47% of farms (production sites)
and 79-84% of retail samples. The organism was detected in 21% of boiled milk
samples and 52-84% in fermented milk samples. The MPRM identified up to ten steps
between the farm and consumption and charcterised each according to the processes
involved. The fermented milk samples were consumed in greater volumes than the
boiled and untreated milk samples. Risk determination using Monte Carlo simulations
and probability modeling suggested the risk of L. monocytogenes was highest with the
fermented milk at the retail market, supporting the findings of the qualitative exposure
assessment. Optimization of the boiling and fermentation processes could effectively
reduce the risk of listeriosis. Summary: This proof of concept study used sophisticating
modeling techniques along with information derived from participatory appraisals,
showing how adapting tools to local contexts can generate useful evidence on food
safety at a fraction of the cost of conventional risk assessment. The assessment was
able to identify high risk products and consumer groups and hence lead to better risk
management.
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