Final answer:
A prep cook diagnosed with shigellosis must immediately be excluded from food handling to prevent the spread of this infection.
Step-by-step explanation:
A prep cook diagnosed with shigellosis should be excluded from food handling. This is important to prevent the spread of the infection to others through food. Shigellosis is a type of food poisoning caused by bacteria. When a food handler is sick, especially with a highly contagious disease like shigellosis, they must not be involved in any tasks where they have direct or even indirect contact with food. Option B, being excluded from food handling, is the correct and responsible action to take. The other options, such as being assigned to dishwashing duty, promoted, or given a pay raise, do not directly address the public health concern of preventing illness transmission through food\