Whatever you do this summer, don’t drink the pool water.
Outbreaks of the gastrointestinal parasite cryptosporidium have been spurting upward since 2009, with the number of outbreaks gushing up an average of 13% each year, according to researchers at the Centers for Disease Control and Prevention. The germ spreads via the fecal-oral route and causes explosive, watery diarrhea that can last for up to three weeks. Most victims pick up the infection from recreational waters, such as swimming pools and water parks.
The main trouble is that crypto is extremely tolerant of chlorine and can happily stay afloat in well-treated pools for more than seven days. Thus, sick swimmers are the main source of infection—often young children who have yet to master toilet skills and also have more of a tendency to gulp pool water. An infected person can shed 100 million parasite eggs in one bout of diarrhea. Knocking back just 10 or fewer eggs in contaminated pool water can lead to an infection.