7 dangerous water-borne pathogens to watch out for this summer

In 1975, it was the blockbuster Jaws—and the fears that it evoked—that kept droves of people out of the water. Now, it’s not sharks, but rather something nearly invisible that may be having a similar effect. A recent rash of reports about flesh-eating bacteria and dangerous algae blooms have dominated headlines, causing concern for swimmers and fishermen across the nation.

But as physicians know, it’s not just ponds, lakes, rivers, and oceans that bathers need to worry about. Even chlorinated swimming pools, hot tubs, and drinking water can be dangerous. Here are seven pathogens that might keep you company—and possibly come home with you—during your next swim or sip.

Vibrio vulnificus

A bug with a bad reputation that appears to be getting worse, Vibrio vulnificus are a type of pathogenic bacteria often referred to as “flesh-eating bacteria.” Infection with V. vulnificus can lead to necrotizing fasciitis, an often-deadly condition in which the bacteria rapidly and progressively eat away at the body’s soft tissue.

Necrotizing fasciitis began making national headlines last year after a man from New Jersey lost all of his limbs after contracting a V. vulnificus infection while crabbing. The bacteria usually take advantage of people with immune systems compromised by conditions such as hepatitis and diabetes, or renal and adrenal issues.

According to the CDC, V. vulnificus typically thrive in US coastal waters during hurricane season (May–October), and most bacterial infections are the result of consuming undercooked or raw shellfish—especially oysters. Open wounds exposed to brackish or salt water can also increase the risk of infection. To avoid V. vulnificus infection, the CDC recommends staying out of brackish or salt water, covering wounds with waterproof bandages if there is a chance of exposure, and proper wound care upon exposure to brackish or salt water. People should also avoid raw seafood or seafood juices.

Cyanobacteria

If you’ve ever seen a pond or lake slick with verdant algae, then you’ve likely seen the product of cyanobacteria overgrowth. According to the EPA, cyanobacteria—also referred to as blue-green algae—often cause harmful algal blooms, which can produce toxins that are dangerous to humans, animals, and aquatic ecosystems.

According to the EPA, exposure to the toxins produced by cyanobacteria may lead to a myriad of symptoms in humans, including abdominal pain, headache, sore throat, nausea, vomiting, dry cough, diarrhea, bloody diarrhea, mouth blistering, fever, tingling, burning, numbness, drowsiness, incoherent speech, salivation, and pneumonia. 

People often contract cyanobacteria infections by ingesting contaminated water, either while swimming or through drinking water. Sometimes, dermal exposure occurs through contact, or if cyanobacteria cells accumulate in bathing suits or diving gear. Shellfish that have accumulated cyanobacteria are also a source of infection.

Escherichia coli

Feces and water don’t mix—or, at least, they shouldn’t. When they do—especially in water that’s used for swimming or drinking—Escherichia coli infections often occur. According to the Mayo Clinic, human and animal feces can pollute surface water, such as streams, rivers, and lakes. Public water supplies, and sometimes water from wells, are treated to kill E. coli, but this isn’t always the case with water used for swimming. Even swimming pools, if insufficiently chlorinated, can harbor E. coli.

To reduce the risk of water-borne E. coli infection, the CDC recommends doing all that you can to avoid swallowing water while in lakes, ponds, streams, swimming pools, and kiddie pools.

Naegleria fowleri

Unlike the previous organisms on this list, Naegleria fowleri is an amoeba with a fondness for the human nose. While N. fowleri infection is rare, it most frequently occurs when people are swimming or diving in fresh water and the amoeba swims up the nose—the only path of infection, according to the CDC. Of note, people cannot get sick by drinking water containing the parasite.

Although infection with N. fowleri—known as naegleriasis or primary amebic meningoencephalitis—is uncommon, it’s usually fatal. The CDC notes that only 4 of 145 individuals have survived the infection from 1962 to 2018. Most recently, a North Carolina man contracted the amoeba after swimming in a man-made lake at a water park, and died shortly thereafter. Symptoms typically mimic those of bacterial meningitis.

Cryptosporidium

Why should E. coli have all the fun? Cryptosporidium is another feces-borne troublemaker.

Cryptosporidium, according to the CDC, holds the superlative of the leading cause of water-borne disease among humans in the United States. This infectious parasite, which causes the gastrointestinal illness cryptosporidiosis, is called crypto for short. Its outer shell makes it resilient to chlorine, meaning it can spread in pools as well as fresh water.

Cryptosporidiosis symptoms include watery diarrhea, stomach cramps or pain, dehydration, nausea, vomiting, fever, and weight loss. To prevent crypto transmission, the CDC says anyone with diarrhea should not swim, and those with a diagnosis of cryptosporidiosis should wait 2 weeks after the diarrhea has stopped to go swimming. In addition, children should not swim in diapers, and diapers should be changed far from the water’s edge. Importantly, the CDC strongly advises to avoid swallowing the water at pools, lakes, and other recreational swimming places.

Pseudomonas aeruginosa

Pseudomonas aeruginosa infections, according to the CDC, are common in healthcare facilities, particularly in patients with compromised immune systems, patients on ventilators, and those with certain types of surgical wounds. However, milder infections can occur in healthier patients upon water exposure. These typically take the form of ear infections in children, skin rashes, and eye infections in people who use extended-wear contact lenses.

Under-chlorinated water is often the cause of these more mild infections, so much so that the resulting skin condition is often called “hot tub rash.” Symptoms typically take the form of itchy spots that turn into a bumpy red rash. Often, the rash is worse on parts of the body covered by a swimsuit. Hot tub rash can also take the form of pus-filled blisters that form around hair follicles. It typically resolves without treatment.

To lower the risk of hot tub rash, the CDC says you should promptly remove your swimsuit and shower after swimming, keep your swimsuit clean, and make sure that the pool, hot tub, or body of freshwater is being properly maintained.

Legionella

Exposure to Legionella bacteria can lead to legionellosis, which can present as two distinct types of illnesses: Legionnaires’ disease and Pontiac fever. Legionella are most commonly transmitted through inhalation of contaminated aerosols. While it’s more commonly spread through water systems—such as cooling towers, decorative fountains, or showerheads—humans can also become infected after aspirating while drinking or while swimming in contaminated water. Legionella commonly reside in lakes, rivers, and streams.

Symptoms of Legionnaires’ disease include pneumonia-like symptoms, such as cough, shortness of breath, fever, muscle aches, and headaches. On the other hand, Pontiac fever, which is less severe, typically takes the form of fever and muscle aches. Treatment of Legionnaires’ disease includes antibiotics while Pontiac fever tends to resolve on its own, according to the CDC.