Whipple's disease is a chronic multiorgan infection caused by Tropheryma whipplei, a weakly staining gram-positive bacillus. Seroprevalence studies indicate that ~50% of people in Western Europe and ~75% of those in rural Senegal have been exposed to T. whipplei. The route of transmission is unclear but probably involves fecal-oral spread and possibly droplet and/or airborne transmission.