Some types of public swimming pools need disinfectant checks more often than others. (CBC)

The U.S. Centers for Disease Control has found that about 12 per cent of public pool inspections it reviewed resulted in immediate closures because of public health concerns.

The CDC review, made public Thursday, was based on more than 120,000 public pool inspections done in 2008 in 13 states, the largest study of its kind.

Of the pools that had to be temporarily closed, 17.2 per cent were in child-care facilities, 15.3 per cent were in hotels or motels and 12.4 per cent were in apartment or condominium buildings.

Each year, 15 to 20 outbreaks of stomach bugs are blamed on pools, the CDC said. Studies suggest a quarter of these are caused by bacteria, viruses or parasites that should have been killed by proper pool treatment such as chlorination.

Improper disinfectant and pH levels in the water can result in transmission of germs that cause gastroenteritis, such as norovirus.

"Among pool types, maintaining adequate disinfectant levels at kiddie/wading pools and interactive fountains is challenging because shallow depth, aeration, sunlight and organic material (e.g., feces, urine, sweat, and dirt) from young children deplete disinfectant," the report said.

"Disinfectant and pH levels should be measured and adjusted more frequently at these pool types."

The CDC recommended that swimmers:

• Don't swim if they have diarrhea.
• Don't swallow pool water.
• Before swimming, shower with soap and wash hands so that germs from the body don't end up in the water.
• Wash children thoroughly, especially the rear end, with soap and water before swimming.
• Check children's diapers often and provide frequent bathroom breaks for older kids.
• Change diapers in a bathroom or diaper-change area away from the pool.
• Gauge the quality of pool water with test strips sold at local stores.

The study is published in the CDC publication Morbidity and Mortality Weekly Report.

With files from The Associated Press