Could also be cryptosporidium. One ill child could infect a whole pool if you swallow some pool water... https://www.google.com/search?hl=en&q=cryptosporidium%

Could also be cryptosporidium. One ill child could infect a whole pool if you swallow some pool water... https://www.google.com/search?hl=en&q=cryptosporidium%20pool%20infected https://www.google.com/search?hl=en&q=cryptosporidium%20pool...