Which disease requires higher levels of disinfection than the others?

• A. Cholera
• B. Hepatitis
• C. Giardia
• D. Norovirus

Answer: (B)

Disinfection effectiveness depends on how resistant a pathogen is to the disinfectant. Protozoan cysts like Giardia have a tough outer shell that protects them from chlorine, so you need a higher disinfectant dose or longer contact time to inactivate them than you do for many other pathogens. Bacteria such as the ones causing cholera are generally more easily inactivated by chlorine, so they require less disinfection. Viruses vary, but many enteric viruses are less resistant than Giardia cysts, though non-enveloped viruses can be tougher than some bacteria. Putting it together, Giardia requires the highest level of disinfection among these options, with viruses needing less and bacteria needing even less. In practice, this means treatment strategies must account for Giardia’s persistence, often using additional barriers beyond basic chlorine disinfection.