Visitors are at risk of ingesting water that has been contaminated with feces at splash pads.
Nineteen of 50 swimmers experienced diarrhea beginning 3 days after their return from a training trip to Puerto Rico.
Pools and hot tubs play host to a wide range of disease-causing microorganisms, warns the CDC.
Experts said reason for the rise isn't clear, but could reflect better surveillance and testing.
The Pan American Health Organization (PAHO) late last week reported 3,100 new suspected or confirmed chikungunya cases, bringing the total in the Americas this year to 250,726.
The previous two reports noted increases of 617 and 32,492 cases, respectively. Brazil, which logged more than 30,000 new cases in the previous report, did not report updated numbers to PAHO for the most recent report, dated Aug 19.
Non-outbreak raw-milk cases may outnumber outbreak cases 25 to 1—and knowing the farmer might not help.
