Symptoms include jaundice, fatigue, stomach pain, nausea, fever, and diarrhea. Treatment is bed rest and fluids. It may be fatal to those with compromised immune systems.

Norovirus is transmitted through oral contact with feces. Transmission through aerosolized water may also be a source. It can survive 10 ppm chlorine. The CDC reported that in 1997, three percent of cases were due to waterborne exposure. Symptoms include stomach cramps, nausea, vomiting, and fever. It generally clears up within 24 to 60 hours.

Shigellosis is a bacterial infection spread through contact with feces. It causes bloody diarrhea, fever, and stomach cramps. Treatment involves antibiotics.

In general, maintaining chlorine or bromine at industry-accepted levels will protect bathers from most of these pathogens. However, as stated in accompanying articles, cyanuric acid, the stabilizer found in dichlor and trichlor, will slow the disinfection process.

According to the Model Aquatic Health Code, there are a large number of references on the effect of CYA on microbial kill times (CT Inactivation Values). In general, they show that the presence of CYA increases CT inactivation values, and the amount of this increase depends on the pH and the ratio of CYA to available chlorine. However, there are few reports that relate specifically to the issue of what levels of available chlorine and CYA are required to maintain a swimming pool in a biologically satisfactory state.

Studies examining the effect of CYA on the disinfection capacity of chlorine show that using CYA or stabilized chlorine slows down the inactivation times on bacteria, algae, protozoa (Naegleria gruberi and Cryptosporidium parvum), and viruses (see accompanying table.)

Because cyanuric acid is known to slow chlorine’s kill speed against these pathogens, it is a good idea to keep levels within industry accepted guidelines – 30 to 50 ppm.

Kill rate of various pathogens with or without CYA