A US company is offering free holidays in Mexico and Guatemala for volunteers on a diarrhoea drug programme…. The trial is in a part of the world where travellers’ diarrhoea is rife. A total of 1,800 volunteers are needed. Intercell‘s clinical director, Nigel Thomas, told the UK’s Independent newspaper: “We are looking for people who have already planned to go to Mexico or Guatemala and think this would add another interesting aspect.