Infection with the protozoan Giardia lamblia causes giardiasis, a diarrhoeal disease usually picked up from food or water carrying its hardy cysts. The cysts survive chlorination better than bacteria, so outbreaks trace to contaminated wells, streams and occasionally fresh produce washed in unsafe water. Symptoms range from silent carriage to cramping, bloating and prolonged diarrhoea with malabsorption. Prevention is straightforward: safe water, thorough washing of produce, good hygiene among food handlers, and filtering or boiling water where supplies are suspect.