Final answer:
A food handler diagnosed with Norovirus must be excluded from their duties to prevent contamination and spread of the virus, due to its highly infectious nature and low infectious dose that can lead to foodborne disease.
Step-by-step explanation:
A food handler must be excluded from an operation if diagnosed with an illness caused by the pathogen Norovirus. This virus is highly infectious and can lead to foodborne disease through contaminated food, primarily due to poor hygiene practices. Norovirus can easily spread as infected individuals may shed billions of virus particles, which are capable of contaminating food if they don't wash their hands properly after using the restroom or when they are sick.
The infectious dose of Norovirus is very small, with fewer than 20 virus particles required to make someone else sick. Considering the virus's significant impact on public health, it is critical for food handlers to maintain strict hygiene standards to prevent the spread of infection. Consequently, any food handler diagnosed with Norovirus must be excluded from working in food-related operations to protect customers and control the spread of the illness.