What is a significant hazard regarding food preparation when ordering a mollusk like mussels in a restaurant that also serves crustaceans?

Cross-contamination from shared fryers, cutting boards, or utensils.

Even if an individual is medically cleared to eat mollusks while having a crustacean allergy, cross-contamination presents a major risk in commercial kitchens. Shared preparation surfaces, such as cutting boards, utensils, and especially shared deep fryers, can easily transfer trace amounts of crustacean proteins (like tropomyosin) onto the mollusk dish. Even these minute traces can be enough to trigger a severe reaction in a highly sensitive person. Therefore, absolute vigilance, including specific inquiries about dedicated preparation areas, is necessary when ordering mollusks in establishments that handle crustaceans.