The most common diagnostic symptom of an intestinal infection is frequent watery stools (diarrhea), which is missing in you and your grandfather's case. Abdominal cramps, throwing up and fever may be present but not always. Fever and chills indicate that you might be experiencing some type of infection but lack of diarrhea indicates that the infection is not intestinal. Other symptoms (cramps and constipation) could be due to an infection outside the intestinal tract. Maybe there is no infection at all but you both experienced a non-infective poisoning. You can request standard blood analyses to confirm an infection. Then , a microbiological examination of the stool is used to confirm, deny, or identify possible intestinal infection.