Ah, a summer day at the beach. You just set up a chair and dig your toes into the warm sand. But heads up: The sand is teeming with all sorts of creepy crawlies, and some of them might be relatively dangerous. Perhaps you'd like to put on your shoes?

In addition to the jellyfish and broken bottles that can make sand hazardous, it can be home to some mean pathogens. From 2011 to 2012, the U.S. Centers for Disease Control and Prevention (CDC) reported 90 disease outbreaks in the U.S. and Puerto Rico linked to recreational water. Many were tied to treated water sources such as pools and waterparks, but other were associated with oceans and rivers.

Here's a look at what you might find:

Hookworms

These parasitic worms made the news when a Canadian couple contracted a hookworm infection while walking barefoot on the beach in the Dominican Republic. Hookworm eggs are passed in the feces of an infected person and are transmitted by walking on infected soil or sand, according to the CDC. Itching and rash are the typical signs of infection. Infections are treatable with medication.

E. coli and other stomach bugs

Wastewater from sewage and other sources can contaminate seawater. Researchers have found fecal bacteria levels in beach sand that are 10 to 100 times higher than in adjacent seawater. They find that bacteria tend to decay more slowly in the sand than in the water, often leaving behind high levels of bacteria such as E. coli. This fecal-contaminated trip to the beach can lead to stomachaches, rashes and diarrhea. A 2012 study, which analyzed sand from 53 California beaches, found E. coli and enterococcus, along with salmonella and campylobacter, which sometimes trigger food poisoning.

Fungi

There are certain fungi called dermatophytes that cause nail and skin infections. They can be spread easily by people, animals, or contact with soil or sand, and these dermatophytes have been found on beaches, according to the American Society for Microbiology (ASM). Common beach fungi include Trichophyton mentagrophytes and Trichophyton rubrum, which can cause fungal infections such as athlete's foot, ringworm and nail infections. They're most common in patients with poor immune systems, but anyone can get a fungal infection. They are typically treated with topical antifungal medications.

Roundworms

dogs playing on beach Dogs can bring more than fun to the beach. (Photo: pencil artist/Shutterstock)

Are dogs allowed on the beach? Then they may be bringing some unsavory friends. One possibility is the Toxocara canis parasite, a type of roundwarm, warns the ASM. It primarily infects dogs, but people can become infected by accidentally ingesting the eggs. If your hands get sandy and you don't have a chance to wash up before lunch, for example, that's how the parasites might get into your system. According to the CDC, in most cases, Toxocara infections aren't serious in humans and most adults may not even notice any symptoms.

MRSA

The superbug MRSA — officially methicillin-resistant Staphylococcus aureus — is a common concern in hospitals. But a warm, wet and highly populated beach environment makes another perfect breeding ground for the infection to spread. A 2012 study of three Southern California beaches found staph bacteria in 53 percent of sand samples and MRSA bacteria in 2.7 percent of sand samples. Scientists are still researching whether MRSA poses a risk to people at the beach, even in those high levels.

Flesh-eating bacteria

Although they sound like something out of a horror movie, flesh-eating bacteria are pretty serious microbes that can enter your system through eating seafood or getting seawater in open cuts. Vibrio vulnificus bacteria live in coastal water, and the concentration is higher in May through October when water temperatures are warmer, according to the CDC. Just wading in water with a wound is enough to get infected, and infections can quickly lead to serious lesions and may require amputation. Cover wounds, if possible, with a waterproof bandage, and wash them immediately when leaving the water.

Norovirus

According to the CDC, norovirus outbreaks are typically found at hospitals, schools, restaurants and cruise ships. However, it is possible to contract the highly contagious virus while at the beach since the virus is most common in areas where people are in close quarters.

In July 2018, nearly 100 people in Maine caught norovirus after swimming at Woods Pond Beach. State officials believe someone who had norovirus contaminated the water. Most of the people who became ill swam underwater, swallowed the water or took care of someone who became ill from being in the water. "It’s highly contagious, so it would appear that there’s a human element there, that somebody had it and was at the beach," Bridgton town manager Bob Peabody told the Portland Press Herald. "I think the message is, if you’re sick or your children are sick, don’t go to the beach."

Symptoms include diarrhea, vomiting, nausea and stomach pain. The best prevention at the beach is to avoid swallowing water and wash your hands with soap after swimming.

Editor's note: This article has been updated since it was originally published in June 2018.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

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