Outbreaks of cryptosporidiosis, or “crypto,” a diarrhea-causing parasitic infection that is most often spread through contaminated water in swimming pools and waterparks, have increased an average of 13 percent per year over the past decade, according to a report from the Centers for Disease Control and Prevention (CDC).

The number of outbreaks did drop in 2017 (the latest year for which the CDC has complete data) compared to the previous two years, but the long-term trend is still upwards, the report makes clear.

This finding, while troubling, isn’t actually all that new. The CDC has issued an annual warning about the rising number of cases of swimming-pool-related infectious outbreaks — including those involving crypto — for several years now.

It’s also not clear, as the health officials acknowledge, whether the rise in crypto outbreaks is due to an increase in the actual number of cases or to better identification and reporting of them.

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But neither of those factors should keep us from paying attention to this latest warning. With its “profuse, watery diarrhea,” crypto is a particularly unpleasant illness, and for people with weakened immune systems, the infection can even be life threatening.

It’s also a good idea for us to pay attention the warning right now, for we are entering two peak months for crypto outbreaks: July and August.

How Minnesota compares

The CDC report identifies 444 crypto outbreaks in 40 states and Puerto Rico from 2009 through 2017. The outbreaks sickened 7,465 people, hospitalized 287 and led to one death.

Health officials define an outbreak as two or more cases tied to a common source.

Those numbers do not, however, reflect the actual number of cases of crypto. Most people who contract the illness mistakenly believe they have some kind of viral “stomach flu” and seldom report it to their doctors. Few link it to swimming in a pool.

On a state map that accompanies the report, Minnesota is identified (along with Ohio) as having the highest relative number of crypto outbreaks during the period studied. But, as the report also points out, that doesn’t mean the actual occurrence of crypto is greater in Minnesota. It may just mean that Minnesota is doing a better job of identifying and reporting outbreaks than elsewhere in the country.

The Minnesota Department of Health (MDH) has identified 79 outbreaks and 3,846 individual cases of crypto from 2009 through 2018. The annual number of reported cases during those years has ranged from 307 in 2011 to 532 in 2018.

Tolerant to chlorine

Crypto is a hard-shelled parasite that is spread through the feces of contaminated humans or animals. It is tolerant to chlorine and can survive in pools for seven days or more. Even a small amount of feces can contain thousands of the parasites — well above the number needed to infect a human.

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Of the outbreaks identified in the study, 35 percent were linked to people swallowing contaminated water in swimming pools or water parks, 15 percent to people coming into contact with infected animals (mainly cattle), and 13 percent to people contracting the illness in child-care settings. Another 3 percent of the outbreaks were linked to people drinking unpasteurized milk or apple cider.

The one death identified in the study occurred when the parasite was transmitted to a patient in a hospital setting.

Prevention is key

“Young children can get seriously sick and easily spread Crypto,” said Michele Hlavsa, chief of CDC’s Healthy Swimming Program, in a statement released with the report.“They don’t know how to use the toilet and wash their hands, or are just learning how. But we as parents can take steps to help keep our kids healthy in the water, around animals, and in childcare.”

Here are the CDC’s tips for protecting yourself, your family — and others — from this nasty infection:

Do not swim or let kids swim if they have diarrhea. If diagnosed with cryptosporidiosis, do not swim until two weeks after diarrhea completely stops.

Do not swallow the water you swim in.

Keep kids sick with diarrhea at home and away from child care.

Wash your hands with soap and water after coming in contact with animals or anything in their environment, especially animal poop. Alcohol-based hand sanitizers do not work effectively on Crypto.

Remove shoes worn in the animal environments (for example, in barns) before going inside your home.

If you drink milk or apple cider, only buy if it has been pasteurized.

FMI: The CDC’s report was published in the agency’s Morbidity and Mortality Weekly Report (MMWR), where it can be read in full.