It causes severe diarrhea in people with lowered immunity , such as those with AIDS in whom it has become an increasing source of morbidity. Transmission occurs through ingestion of fecally contaminated materials typically from animals to humans, humans to humans, and through contaminated water.
Risk factors are travel to areas with poor sanitation, and having a suppressed immune system.
The incidence is 3 out of 10,000 people. In the last few years several large outbreaks have occurred in major cities when municipal water supplies became contaminated. These outbreaks affected thousands of people. Proper sanitation and hygiene are necessary for prevention. Symptoms usually go away in 7 to 21 days.