Abstract
Giardia lamblia is a parasitic protozoa which is transmitted in the form of a cyst through untreated water and also treated drinking water. Since its presence in water has led to frequent outbreaks of giardiasis and death in many countries, the removal and disinfection of this protozoan cyst from the water supply are of great concern for public health. This study examined the disinfection characteristics of G. lamblia cysts isolated from a Korean patient with giardiasis. When using sodium hypochlorite including 5 or 10 ppm chlorine, the killing rate was initially rapid, however, the disinfection slowed down and a 3log reduction could not be achieved even after 2h. The disinfection effectiveness was also reduced at a lower temperature, thereby implying that the risk o a giardiasis outbreak will be higher in the winter season. A CT (concentration$.$time) curve was constructed based on the results with sodium hypochlorite for use in designing and predicting disinfection performance. The organic chlorination disinfectant SDIS (sodium dichloroisocyanurate) produced a lower pH and a much higher residual effect than sodium hypochlorite. The disinfection of cysts by SDIC continued steadily throughout 2h of contact, although the initial killing rate was lower than that with sodium hypochlorite.