Certified in Public Health (CPH) Practice Exam

Which of the following water-borne disease organisms is very difficult to kill by chemical disinfection of drinking water supply systems?

1. Vibrio cholerae (causes cholera)

2. Cryptosporidium (causes Cryptosporidiosis)

3. Giardia lamblia (causes Giardiasis)

4. E. coli (causes acute gastroenteritis)

The correct answer is: Cryptosporidium (causes Cryptosporidiosis)

Cryptosporidium is indeed very challenging to eliminate through standard chemical disinfection methods commonly used in water treatment, such as chlorination. This organism has a thick protective cyst wall that allows it to withstand harsh environmental conditions and resist the effects of chlorine and other disinfectants. As a result, when Cryptosporidium is present in drinking water, it can survive and lead to outbreaks of cryptosporidiosis, a disease that causes gastrointestinal distress. To effectively kill Cryptosporidium in water supplies, other treatment methods such as filtration through membranes or UV disinfection must be utilized. These alternatives are necessary due to the resilience of Cryptosporidium, which distinguishes it from other water-borne pathogens listed in the question. While Vibrio cholerae, Giardia lamblia, and E. coli can also be concerning in terms of water contamination, they are generally more susceptible to chemical disinfection methods compared to Cryptosporidium.