Public health officials examined data from 46 states and Puerto Rico for the report and found that hotel pools and hot tubs contributed to about one-third (32 percent) of the outbreaks. Public parks came in second (23 percent), then club/rec facilities (14 percent) and water parks (11 percent).
While no significant trend was observed after 2007, the CDC said outbreaks caused by the parasite Cryptosporidium, also known as crypto, increased 25 percent per year between 2000 and 2006.
Of the 363 outbreaks with a microorganism as the culprit, 58 percent were classified as Crypto.
Crypto can spread when people swallow something that's come into contact with an ill person's feces, such as pool water contaminated with diarrhea, according to the CDC.
"Swallowing just a mouthful of water contaminated with Crypto can make otherwise healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration," the CDC states on its website.
The parasite is highly resistant to pool chemicals aimed at cleaning the waters, including chlorine and bromine.
The CDC recommends anyone, adults or children, who has experienced diarrhea should wait two weeks before getting in pools, hot tubs or other public water containers and parks.
Additionally, avoid swallowing water when swimming, rinse off in the shower before entering the water and take children on bathroom breaks often.
Unlike Crypto, parasites Legionella and Pseudomonas can both be effectively controlled by halogens (chlorine, bromine) if the water is properly dosed. Unfortunately, 20 percent of public pools and hot tubs aren't properly dosed with disinfectant.
Legionella can lead to a pneumonia-like condition known as Legionnaire's disease or a flu-like condition called Pontiac fever. Legionella is transmitted when aerosolized water droplets often produced by hot tubs and spa jets are inhaled.
The number of outbreaks caused by Legionella increased 14 percent per year, according to the CDC report, but only accounted for 3 percent of the 363 identified microorganism outbreaks.
Pseudomonas, transmitted when skin comes in contact with contaminated water, may lead to rashes near the ear canal and otitis externa (or swimmer's ear). Pseudomonas accounted for about 4 percent of the 363 outbreaks.
7 Simple Summer Safety Tips