Can stomach viruses or food poisoning be contagious? multiple family members getting nausea, fever, vomiting, diarrhea?

Yes, if you eat the same food, or other contact with each other, or touch contaminated surfaces, or not washing hands thoroughly after bowel movement.

Typical for stomach viruses to cause symptoms for the majority of people involved, stool studies will be critical to identify the actual microorganism causing the outbreak.

People eating the same food may be affected by the same bug or toxin in the food without the persons being contagious. Stomach viruses like other viruses, can be transmitted through food. Norovirus is especially contagious. Hand hygiene, proper cooking and refrigeration of food are critical. Affected members should drink enough water to stay hydrated.