Eight Diseases To Watch Out For At the Beach

Forget sharks: These potentially deadly pathogens and parasites can lurk in sand and sea

Seawater viruses
Seawater contains hundreds of viruses, revealed with dye in the flask on the right. Most are harmless, but some microbes living under the sea and amid the sand aren't. Photo: © Karen Kasmauski/Corbis

Despite its idyllic facade, the beach can be a dangerous place—and swimmer’s ear, sunburn and jellyfish stings may be the least of your worries. Beaches can get pretty dirty, and this pollution can come with some nasty pathogens.

These days a bevy of bacteria, viruses and parasites pop up in the water and in the sand around coasts and freshwater locales alike. Between 2009 and 2010, the U.S. Centers for Disease Control and Prevention (CDC) counted 81 disease outbreaks in the United States and Puerto Rico tied to recreational waters. Many were traced to treated water sources such as pools and waterparks, but some occurred in natural settings like rivers and beaches.

Many of the pathogens found at beaches are treatable, especially if caught early. Rinsing off and generally washing your hands after leaving the beach can reduce the chance of infection. So by all means, swim in the lake or ocean and frolic in the sand. Just be wary of these potentially deadly creatures lurking along the shore:

“Flesh Eating” Bacteria

(James Gathany/CDC)

Vibrio vulnificus is a pretty gnarly microbe. Eating raw oysters that harbor V. vulnificus results in nausea, diarrhea and abdominal pain. For swimmers with open wounds, V. vulnificus infections can break down skin and cause ulceration, leading to its movie-monster moniker. Early treatment with antibiotics improves patients’ chances, but severe cases sometimes require amputation.

This summer, a Florida news outlet claimed that a whopping 32 cases of V. vulnificus had popped up in the state, leading many media outlets to report that Florida was staving off an attack of flesh-eating bacteria. The report’s numbers were a bit off. According to the Florida Department of Health, the state has seen 15 cases with 3 confirmed deaths as of August 8.

On average, the US sees 95 cases of V. vulnificus per year, with 85 hospitalizations and 35 deaths, the CDC reports. Roughly half of these occur across the Gulf of Mexico region. Beachgoers should be careful of entering the water with open wounds, and seafood eaters should consider cooking their shellfish. 

Stomach Bugs

(Anna Tanczos/Wellcome Images )

Beach sands can harbor a slew of stomach bugs, which can cause bouts of nausea and cramping or even severe gastroenteritis. A 2009 study in the American Journal of Epidemiology found that digging in beach sand (and being buried in beach sand) raised the risk of diarrhea. Beachgoers could come down with some familiar pathogens, such as Salmonella, E. coli and norovirus—the most common stomach flu in the U.S., seen here. Parasites such as Giardia and Campylobacter are also on the watch list.

The prevalence of stomach bugs at the beach comes down to one thing: poop. Traces of fecal contaminants and microbes have been found in sand samples and in some water samples at both freshwater and marine beaches. How does poop end up at the beach? Some studies point to human sewage contamination from nearby treatment plants. But fecal pollution also shows up at beaches far from treatment facilities. Storm surges and heavy rainfall could carry human waste further from a source, or wild animals may contribute their droppings.

Keep in mind, seawater that renders 36 out of 1000 swimmers sick with gastroenteritis is acceptably clean by EPA standards.


(© Kari Lounatmaa, Stuart Painter/Science Photo Library/Corbis)

A more common worry in hospitals, antibiotic-resistant bacteria have infiltrated the ocean too. With high human traffic and generally warm waters, beaches provide an ideal breeding home for Methicillin-resistant Staphylococcus aureus, or MRSA.

Regular Staph infections begin as small bumps that look like bug bites or pimples, but they can progress into large abscesses—even growing deeper into the body and threatening bones and vital organs. Severe cases turn into pneumonia and other forms of respiratory distress. Antibiotic ointment can usually treat minor skin infections, but more serious cases require intravenous antibiotics and surgery.

In subtropical ocean waters, swimmers have a roughly 37 percent chance of encountering some form of Staph bacteria, though some estimates put that number closer to 50 percent. For MRSA specifically, a 2009 study found it at five out of ten public beaches along Puget Sound. And a 2012 survey of three California beaches found MRSA in 1.6 percent of seawater samples and 2.7 percent of sand samples. MRSA has also been found in freshwater lakes and beaches, though one study suggests it has better survival chances in marine water because Staph consumes salt as a nutrient. Some researchers posit that beaches represent an ecosystem where the bacteria can swap genes, particularly those associated with antibiotic resistance. 

Pontiac Fever & Legionnaire’s Disease


Legionella bacteria, the microbes behind these illnesses, happily grow in warm freshwater. Their sweet spot falls between 95 and 115 degrees Fahrenheit, which means they absolutely love hot tubs. The bacteria latch on to water vapor particles, and people contract the disease by inhaling contaminated mist or steam. At the beach, the most likely place you’d come across Legionella is in a public shower. In 2007, researchers found that water from 7 of 36 beach showers across southern Italy tested positive for L. pneumophila, the most common strain behind the illness.

The mild version is just a chest infection dubbed Pontiac Fever, which goes away in two to four days. A more severe form of Legionella infection, Legionnaire’s disease, looks a lot like a serious case of pneumonia, with coughing, fever and muscle aches for up to two weeks. The CDC estimates that about 8,000 to 18,000 infected people wind up in hospitals across the U.S. Normally, a round of injected antibiotics does the trick, but roughly 15 percent of cases prove fatal.

While Legionella is a freshwater microbe, a 2005 survey by researchers at Woods Hole Oceanographic Institution found 32 types of the bacteria in seawater from Mount Hope Bay in New England. None were infectious (most strains aren’t), but the results hint that the bacteria may find warmer seawater more hospitable, a potential added worry for beachgoers. 


(Erskine Palmer/CDC/Microbe World)

Improperly handled medical waste could expose some swimmers and surfers to hepatitis. Viral hepatitis—most commonly in the form of A, B or C strains—inflames the liver. Most strains are typically transmitted through blood and fecal matter. In its most severe forms, including hepatitis C, patients get cirrhosis of the liver and even cancer. In its mildest form, hepatitis A, patients are laid up for up to six months.

Globally, only a handful of cases of hepatitis A have been linked to recreational water, according to the World Health Organization. And while hepatitis E has turned up in some water samples, so far recreational waters have not been linked to any cases.

In the UK, though, one study showed a correlation between surfing and a higher risk of getting hepatitis. So when it turns up in local waterways, communities are quick to act. A 2006 study by researchers at San Diego State University found hepatitis A in 79 percent of water samples. Now, non-profits and public health groups run vaccination programs for surfers at San Diego’s Imperial Beach, which suffers from pollution linked to sewage runoff. 

“Brain-Eating” Amoeba


Infections of Naegleria fowleri, the so-called brain-eating amoeba, are extremely rare. Only freshwater beachgoers need to worry about this one, because N. fowleri frequents the warm waters and soils of freshwater lakes and ponds.

Entering a swimmer's body through the nose, N. fowleri is lured up the olfactory nerve by neurotransmitter chemicals until it reaches the brain. Normally, N. fowleri lives off bacteria, but once in the brain, it eats what’s in front of it, inducing a condition called primary amebic meningoencephalitis, or PAM. Initial symptoms look like stomach flu—headache, vomiting and fever. But unlike your average stomach bug, PAM is typically fatal. As the infection becomes more severe, an infected person has seizures, hallucinations and can fall into a coma.

Only eight cases of PAM due to N. fowleri exposure proved fatal between 2007 and 2008, and the CDC only counts 28 total cases linked to recreational waters between 2003 and 2012. According to the CDC, drinking water that contains N. fowleri won't make you sick—acids in the stomach probably kill the free-swimming microbe on the spot.

Cercarial Dermatitis

(CDC/Minnesota Department of Health)

Commonly known as swimmer’s itch, this patchy skin rash is caused by exposure to trematode parasite larvae in freshwater. It manifests within 48 hours of exposure and can last for up to seven days. Normally these parasites infect snails and then jump to ducks and other birds, but they occasionally infect humans as well.

First identified at Lake Michigan in 1928, trematode parasites only inhabit freshwater lake beaches. In marine environments, the term “swimmer’s itch” may refer to rashes caused by contact with larva from thimble jellyfish and other cnidarian species. Treating the rash with an antihistamine or corticosteroid cream may provide relief. 

Bloomin’ Algae

(© Kevin Schafer/Corbis)

Most algae living in the surface waters of oceans and lakes are pretty tame. But some algae produce nasty toxins. This becomes a bigger problem when runoff carries nutrients like nitrogen and phosphorus into waterways and triggers population explosions known as blooms. Harmful algal blooms can poison shellfish and contaminate regional drinking water. Swimmers can inhale algal toxins through water vapor, swallow them or absorb them through the skin.

In freshwater, the biggest concern is blue-green algae, or cyanobacteria, which likely caused 11 of the disease outbreaks reported to the CDC between 2009 and 2010. Some strains of cyanobacteria produce toxins that can damage your liver, while others target the nervous system. According to the CDC report, just touching the algae produced rashes, swelling and skin sores. Swimmers who ingested or inhaled contaminated water got a range of symptoms such as diarrhea, nausea, cramps, coughing, wheezing, congestion and ear infections. 

In saltwater ecosystems, dinoflagellate algae like Karenia brevis are the main culprits behind harmful blooms called red tides. K. brevis produces brevitoxins, chemicals that disrupt nerve cell signaling. For swimmers this may translate to trouble breathing, sore throats and irritated eyes.

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