Invisible danger could be lurking in the water: How to stay safe this summer

A recent alarming spate of infections at a Virginia lake offered a stark reminder for summer enthusiasts to use caution and good hygiene at outdoor water spots.

Virginia state health officials said 20 people who visited Lake Anna, a recreational site south of Washington, D.C., in late May were diagnosed with an E. coli infection and came down with stomach illness. Of those, five people developed a serious complication called hemolytic uremic syndrome, a rare condition that damages kidneys, said Katherine McCombs, deputy director of surveillance and investigation at the Virginia Department of Health Office of Epidemiology.

The Virginia case highlights the need for visitors to lakes and recreational water spots to be cautious about bacterial diseases and other potential dangers lurking in the water.

"Water can have bacteria in it - and certainly not just for E. coli, but for lots of other things," said McCombs.

As we careen into summer, USA TODAY is highlighting some key water-borne threats that may not be visible to the naked eye.

How often do people get sick from lakes?

Swimming in lakes, rivers and oceans can expose people to various pathogens.

Since 2009, more than 2,700 people have become ill in more than 100 outbreaks at such outdoor water spots that had not been treated with chlorine or did not have filtration systems, according to the Centers for Disease Control and Prevention. Dozens of people were hospitalized after falling ill from stomach bugs or other illnesses at these sites.

People are especially vulnerable to lake and water-based pathogens in the summer, likely because hotter weather prompts people to seek cool water. June, July and August are the most common season for people to become sickened at lakes and other outdoor water spots, according to CDC data.

A CDC study said outbreaks from germs in recreational water often stem from pathogens such as norovirus and E. coli. These pathogens can come from human feces, vomit, stormwater runoff, sewage or septic system malfunctions. Animal waste in recreational hotspots can carry pathogens if people swim or play in contaminated waters.

Beware of brain-eating amoebas, too

Another rare but often fatal risk involves the amoeba Naegleria fowleri, a brain-eating amoeba. Last August, a Travis County, Texas resident died after becoming infected during a swim at Lake Lyndon B. Johnson, outside of Austin.

Brain infections, called amoebic meningitis, can occur in freshwater lakes with this amoeba when water is forced up the nose during an activity such as diving or water skiing. Such infections generally do not occur in salt water or properly maintained and chlorinated pools.

Following the Travis County resident's death, Austin-Travis County Health Authority Dr. Desmar Walkes warned residents to beware that microbes exist, especially during warm weather months that “make it ideal for harmful microorganisms to grow and flourish."

Watery diarrhea and crypto

Generally, filters and chlorinated water in swimming pools and hot tubs generally make them safer than watering holes. But germs can still lurk, depending on how well they are maintained. One study noted that the U.S. lacks national standards for recreational water spots such as pools, hot tubs and splash pads.

In one case, more than 2,300 people were infected at a New York splash pad rife with the germ Cryptosporidium, a parasite that causes watery diarrhea. In response to the outbreak, New York passed public health regulations that mandated splash pads have ultraviolet light systems to kill these microscopic germs, according to the CDC.

In the case of this germ, chlorine is not enough to kill it off: The microscopic "crypto" germ, spread through the fecal matter of an infected person, can survive a week in water that's been disinfected with chlorine or bromine. Kids, pregnant women and people with weakened immune systems are especially vulnerable to this common public swimming pool bug, according to the National Institutes of Health.

Virginia lake outbreak probe continues

McCombs, of the Virginia Department of Health, said the state was awaiting the results of water test samples drawn from Lake Anna. The tests typically take about 48 hours to complete.

Health officials also interviewed the 20 people infected with E. coli to ensure there wasn't a common cause for the illness, such as eating the same type of contaminated food or exposure to an infected person.

"We're still at the point of gathering a lot of information to see if we can rule out any of those factors," McCombs said.

She said E. coli outbreaks are often linked to consuming contaminated and undercooked foods, such as the outbreaks linked to romaine lettuce, but contaminated water can also be a source of infection.

"We're used to it (E. coli) being more of a foodborne thing, but it certainly can be transmitted through water as well," McCombs said.

Take these steps to stay safe when swimming, boating natural waters

McCombs also advised people to avoid swimming with cuts or wounds that could be exposed to bacteria in the water. People with a stomach or another type of illness that causes vomiting or diarrhea should also avoid the water because they can expose others to germs in their system. McCombs also suggested hand washing before eating or preparing food or after using a restroom, if you want to get rid of bacteria.

Some other tips:

  • Avoid swimming near storm drains;

  • Avoid swimming if you are ill;

  • Do not enter water if there is a green film on the water;

  • Shower after swimming;

  • Avoid swimming for three days after a heavy rain;

  • Dispose properly of human and dog waste.

People swimming or boating in lakes and other natural waters should also avoid swallowing water, McCombs said.

This article originally appeared on USA TODAY: Health risks lurk in water: How to stay safe from disease