Exposure assessment to staphylococcus enterotoxins in Nile tilapia (Oreochromis niloticus) supplied through semi-regulated and unregulated value chains

The objective of this study was to estimate the risk associated with staphylococcal enterotoxin (SE) exposure from the consumption of Nile tilapia supplied through the semi-regulated and unregulated value chains in Kenya. The fish supply chain was modeled from landing to consumption of unprocessed (fresh) and processed (salted and sun-dried, smoked, filleted) fish.

Data related to the prevalence of Staphylococcus aureus in fish, taking into account survey information on handling, storage, processing and consumption of Nile tilapia were collected from recently completed studies in Kenya. Other model inputs were complemented with data from published and unpublished literature.

A probabilistic exposure model was developed with Monte Carlo simulation in Excel add-in software using @Risk software. The simulated levels of S. aureus in fish after handling and storage of salted and sun-dried and smoked fish ranged between 4 log CFU/g and 9.01 log CFU/g (maximum population density), while in fillet, levels of S. aureus following growth during display at retail shops was between 3.10 log CFU/g (5% percentile) and 9.01 log CFU/g (95% percentile).

Estimated SE dose per-serving in fish supplied after processing was significantly higher (p < 0.05) in the unregulated (ranged between 0.000150 ng (5% percentile) and 30.0 ng (95% percentile)) than semi-regulated chain. The model revealed that the factors with the highest impact on dose of SE per-serving were the time taken to sell the fish at street markets under ambient conditions and refrigerated fish fillets at retail shops followed by cross-contamination from fish handlers most.

The model simulated a zero risk of exposure to SEs from fish supplied via the semi-regulated and unregulated value chain if cross-contamination from handlers was eliminated. Therefore, this highlighted the need for good hygiene practices during the handling and storage of fish along the value chain.

A significant reduction in the risk of exposure to SE in processed fish was noted when shelf-life was reduced to a maximum of 72 h. Although the model can be used in risk assessments of fish supplied under the same scenarios, the current study revealed data gaps that need to be addressed to improve the risk assessment.