Hello and welcome to HCM. Thank you for your query. I understand your concern and shall explain every aspect of your query in detail for your satisfaction. The appearance of diarrhea and other gastric events mentioned by you in your query indicates a contamination of the food that was served to you either at the resort or elsewhere at Costa Rica. It is quite common for tourists to find it more difficult to adjust to local food while travelling, as they are most often not accustomed to or resistant to local infection-causing organisms. The first and most important thing would be to initiate a course of antibiotics (in case the symptoms are caused by an infection-causing organism, along with probiotics (to promote digestion), oral rehydration powders or solutions to keep your husband and you hydrated, antacids (to reduce abdominal irritation) and if required a pain and fever management medication. The reason why your husband has been experiencing swollen/sore gums is because: vitamin B12 and folate are vital nutrients which are absorbed by the lower intestine. In case of gastrointestinal problems (GIT) like indigestion, irritable bowel syndrome, infections causing diarrhea; these nutrients are not absorbed and are thus lost along with the diarrhea. Symptoms of low vitamin B12 and folate are sore and swollen gums. This is the most probable scenario. I hope I have succeeded in explaining this. You could request the doctor to initiate a course of multivitamins, or wait till the stomach flu clears, and his gums/oral cavity shall surely improve. In the meantime, please keep him hydrated, avoid oily/fried/fatty food. Stick to boiled and bland food. Preferably a liquid diet. I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications. I would gladly help you. Best wishes.