I live in Bangkok, and in my opinion food courts in Tesco are better than Big C. Do you want know 3 obscure food court locations in the Chidlom area? An inexpensive one is on the 4th floor of the Amarin Building, located near the west exit of ChiIdlom Station. The other two are in Central Embassy at east exit of the station. The first one is Central Food Hall on the 7floor. This is an upscale version where you order at the food station, and they deliver it to you table. The real gem is in Cemtral Embassy LG level. It is called Eathai and it is a symphony of different styles and types of Thai foods.
On a different note, you can get a viral gastroenteritis illness from other sources besides food. One of the most common transmissions is contact with contaminated surfaces. That is why I never touch a door handle when exiting the public bathroom, as many people open the door to leave without washing their hands. The next time you are in a public restroom in Bangkok, watch how many people really wash their hands before leaving and opening the door. You be surprised. I have never come down with viral gastroenteritis or food poisoning in the 6 years I have lived here by taking basic precautions. I have eaten from street vendors not only in Bangkok, but also in small towns and villages. So don’t blame all the street vendors for the nasty stomach viruses because you may have contracted elsewhere.