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Aquatic Toxins Nursing CE Course

1.5 ANCC Contact Hours

About this course:

This learning activity aims to increase the learner's knowledge of fresh and saltwater toxins, harmful algal blooms (HABs), and the risk of human illness. This includes understanding the cause, signs and symptoms, diagnosis, and treatment following exposure. This activity also explains how to prevent infection and implement safe water techniques.

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This learning activity aims to increase the learner's knowledge of fresh and saltwater toxins, harmful algal blooms (HABs), and the risk of human illness. This includes understanding the cause, signs and symptoms, diagnosis, and treatment following exposure. This activity also explains how to prevent infection and implement safe water techniques.  

After completion of this activity, the learner should be able to:  

  • identify aquatic toxins found in freshwater and saltwater 

  • discuss Vibrio vulnificus exposure, medical management, and outcomes 

  • discuss Naegleria fowleri exposure, medical management, and outcomes 

  • explore the effects of harmful algae blooms  

  • define safe recreation in freshwater and saltwater and how to prevent infection from aquatic toxins  


Recently, there has been increased awareness of individuals impacted by exposure to toxins in the ocean and freshwater. From the elderly man who died from "flesh-eating bacteria" to the child who died from a "brain-eating amoeba," there is no shortage of fear of entering the water for recreation. Considering most of the US is surrounded by water, and many states have multiple freshwater lakes, much of the available data on this topic relates to anywhere residents and tourists seek recreation in bodies of fresh or saltwater (Lavery et al., 2021).  

The economic impact of aquatic toxins and harmful algal blooms (HABs) is staggering. In the last 10 years, the cost of algal blooms in 85 cities across 22 states has reached over 1 billion dollars. The states experiencing the highest costs include Ohio at $815,184,000, Oregon at $75,000,000, and Texas at $66,859,627. Much of the money spent in Ohio has been due to recurrent HABs on Lake Erie, which, notably in 2014, led to Toledo's tap water being declared unsafe, leaving nearly 500,000 people without water for drinking or cooking. This amount is 70% of the total cost of all other locations. The 2018 HAB at a lake outside the capital city increased the overall cost to Oregon. HABs also impact health. One study by Lavery and colleagues (2021) showed that 321 US emergency room (ER) visits between 2017 and 2019 were attributed to exposure to toxic algae. The results of this study were limited as only 70% of ER visits were included in the study, and many of the ER visits included were based on ICD-10 coding alone. Most ER visits were in region 4 of the US, including Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee (City of Toledo, 2022; Lavery et al., 2021; Schechinger, 2020).  

Saltwater Bacteria 

Many health concerns occur in salt and brackish water, a mixture of fresh and saltwater, "where the river meets the sea." One of the bacteria that thrive in saltwater is Vibrio. Vibrio are gram-negative bacteria naturally found in warm, salty marine environments. Vibrio are prevalent in higher concentrations in coastal waters between May and October as water temperatures rise. This timing coincides with hurricane season, severe storms that affect the coastline and allow seawater to come inland during flooding (Centers for Disease Control and Prevention [CDC], 2019a, 2020).  

There are over 20 Vibrio species that cause the human illness known as vibriosis. Vibriosis causes an estimated 80,000 illnesses (52,000 from consuming contaminated food), 500 hospitalizations, and 100 deaths annually in the US. The three most common disease-producing species found in the US include Vibrio parahaemolyticusVibrio vulnificus, and Vibrio alginolyticusVibrio can cause disease in two primary ways within coastal waters. First, it can be contracted by eating raw or undercooked seafood. Undercooked or raw oysters seem to produce the highest risk

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for disease development. The second route of infection is through skin exposure in the presence of an open wound when exposed to contaminated saltwater or brackish water (CDC, 2020).  

Vibrio vulnificus 

The countries with the most cases of V. vulnificus are the US, South Korea, Taiwan, Japan, and Mexico. There is a correlation between global warming, the resulting increase in water temperatures, increased water salinity, and an increase in the prevalence and virulence of the organism. This increase in water temperature has also allowed V. vulnificus to thrive in climates further north than they have been found in the past (Haftel & Sharman; Morris, 2021).  


Although anyone can become infected with V. vulnificus, some individuals have an increased risk of developing an infection and serious complications, such as those with preexisting conditions, including: 

  • chronic hepatic disease: hepatitis, cirrhosis, hemochromatosis 

  • renal disease 

  • malignancy 

  • diabetes 

  • human immunodeficiency virus (HIV) 

  • thalassemia (Haftel & Sharman, 2022) 

Men tend to be infected more frequently than women, and individuals over 40 are more at risk. This sex and age difference may be due to this group's increased prevalence of hepatic disease. Due to the increased exposure to saltwater, fishermen, scuba divers, surfers, and snorkelers are at an increased risk of infection (Haftel & Sharman, 2022).  

Signs and Symptoms  

Depending on the route of entry, V. vulnificus can cause three distinct infection presentations: primary septicemia, gastroenteritis, or wound infection. The ingestion of V. vulnificus can lead to gastroenteritis or primary septicemia. In primary septicemia, the portal into the bloodstream is thought to be through the small intestine or colon. Gastrointestinal (GI) symptoms of watery diarrhea, abdominal cramping, nausea, vomiting, fever, and chills may be present with septicemia. Symptoms can progress rapidly, and by the time medical intervention is sought, 33% of patients present to the hospital already in shock or become profoundly hypotensive within 12 hours of admission. This presentation of infection accounts for 60% of all V. vulnificus infections, with a mortality rate of 50% (Haftel & Sharman, 2022; Morris, 2021).  

Gastroenteritis presentation overlaps the symptoms of septicemia with sudden onset of diarrhea, nausea, vomiting, fever, and chills. Although most people recover from this type of infection, this presentation must be treated aggressively because these same GI effects can occur before septicemia. This presentation of infection accounts for 10%-15% of all V. vulnificus infections. It usually resolves within 3-4 days without lasting effects (Haftel & Sharman, 2022).  

In the case of wound infections, the bacteria enter the body through a preexisting laceration, puncture, or abrasion and quickly colonize. This can occur through the exposure of the open area to contaminated water, shellfish, or fish. This exposure initiates an intense skin reaction, including cellulitis with large blisters that can rapidly progress to necrotizing fasciitis with myonecrosis (fast spreading soft-tissue infection). Necrotizing fasciitis is commonly referred to as flesh-eating disease. It causes necrosis of the muscle fascia and subcutaneous tissue and spreads rapidly. It is often life-threatening, requiring early diagnosis and aggressive treatment. Infection with V. vulnificus usually requires admission to an intensive care unit (ICU) and limb amputation; however, despite this, the overall mortality rate is 25%, with some patients dying within 1-2 days of becoming ill. The mortality rate increases to 54% in patients with preexisting hepatic or immunosuppressive disease (Haftel & Sharman, 2022; Wallace & Perera, 2021).  


A diagnosis of V. vulnificus should be considered as a possible cause of an infected wound recently exposed to salt or brackish water or signs of septicemia after the ingestion of shellfish. A wound or stool culture should be obtained based on patient presentation. The confirmation of a diagnosis of V. vulnificus infection is based on the presence of the bacteria in the patient's wound, blood, or stool culture. These cultures should be sent to the public health laboratory. Blood cultures are recommended for a febrile patient presenting with hemorrhagic bullae (blisters) or any other signs of sepsis. It is recommended that all V. vulnificus isolates be forwarded to the local public health laboratory (CDC, 2020; Haftel & Sharman, 2022; Morris, 2021).  


In mild cases of gastroenteritis due to V. vulnificus, oral fluid replacement for diarrhea is recommended, along with anti-diarrheal, antipyretic, analgesic, and antiemetic medications as needed. In more severe cases, intravenous (IV) fluids may be required for fluid replacement. Fluid intake, urine output, electrolyte levels, and renal function should be monitored closely (CDC, 2020; Haftel & Sharman, 2022). 

Treatment must be initiated promptly for more severe cases, as antibiotics have been shown to improve mortality rates. Wound infections must be thoroughly assessed. Rapid debridement and possible fasciotomy should be performed to hopefully control the infection and prevent the need for limb amputation. Patients that present with septic shock should receive prompt and aggressive resuscitative efforts following facility sepsis protocols and antibiotic therapy. Patients with antibiotic treatment delayed past 72 hours have a 100% mortality rate (Haftel & Sharman, 2022; Morris, 2021).  

Susceptibility reports have shown that third-generation cephalosporins, tetracyclines, carbapenems, fluoroquinolones, sulfa-trimethoprim, piperacillin-tazobactam, and aminoglycosides are all effective against V. vulnificus. For the best outcomes, combination therapy is recommended. A third-generation cephalosporin (cefotaxime [Claforan] 2 g IV every 8 hours or ceftriaxone [Rocephin] 1 g IV daily) combined with either a fluoroquinolone (ciprofloxacin [Cipro]) 500 mg orally twice daily or tetracycline (doxycycline [Vibramycin, Doryx] 100 mg orally twice daily or minocycline [Solodyn, Minocin] 100 mg orally twice daily) have been used successfully. When treating children, trimethoprim-sulfamethoxazole (Bactrim) plus an aminoglycoside such as gentamycin (Garamycin) is preferred due to the contraindication for doxycycline (Vibramycin, Doryx) and fluoroquinolones such as ciprofloxacin (Cipro) within this age group. Although these recommendations are best practice, recently, antibiotic resistance has been found in 50% of V. vulnificus infections. For topical infections, silver sulfadiazine can be applied to cover the wound (Haftel & Sharman, 2022; Morris, 2021).  


The CDC (2019a) provides strategies nurses can share with patients to protect them from Vibrio vulnificus infections. Patient education should include the following: 

  • avoid brackish or saltwater with an open wound; if entering brackish or saltwater with an open wound, the area should be covered with a waterproof bandage to prevent direct contact with the water 

  • wounds should also be covered if handling raw seafood or the juices from raw seafood; for example, those working in the restaurant and fishing industries  

  • if a wound comes into contact with brackish or saltwater, raw seafood, or the juices from raw seafood, it should be washed immediately with soap and water  

  • if a skin infection or sensitivity develops, seek treatment quickly and alert the healthcare provider (HCP) that exposure to saltwater or raw seafood has occurred  

  • avoid eating raw or undercooked oysters or other shellfish 

  • wash hands after handling raw seafood (CDC, 2019a; Schwartz, 2021).  

The nurse should remind all patients with a chronic disease or immune-compromised state to avoid eating raw seafood, especially raw oysters. This is essential education for cancer patients receiving chemotherapy, as they are highly susceptible to infection due to neutropenia, or the lack of neutrophils, secondary to treatment (Morris, 2021). 

Freshwater Amoeba 

Naegleria fowleri 

Naegleria fowleri is a free-living, thermophilic (heat-loving) microscopic amoeba (single-celled living organism) commonly found in warm bodies of freshwater, including lakes, rivers, or hot springs. It infects an individual when contaminated water enters the nose. Once N. fowleri enters the nasal passageway, it travels to the brain. Once in the brain, it causes primary amebic meningoencephalitis (PAM), which is how it came to be known as the "brain-eating amoeba." Since N. fowleri prefers warm bodies of water, it is commonly found in Florida and other southern states with warm climates. N. fowleri is the only Naegleria species known to infect humans. Infection often occurs when people engage in water activities in freshwater, such as swimming or diving. Infection can, although less likely, occur from other contaminated sources of freshwater such as swimming pools that are inadequately chlorinated or tap water. It is important to note that the amoeba can only cause infection when it enters the body through the nasal passage; infection cannot occur by ingesting contaminated water orally. This amoeba has a specific life cycle (See Figure 1) that affects transmission and subsequent disease (CDC, 2021b; Minnesota Department of Health, 2018; NC Department of Health and Human Services [NCDHHS], 2019).  

While PAM has been detected in Florida since the early 1960s, new cases have been diagnosed in other southeastern states such as Texas and even northern states such as Indiana, Kansas, Missouri, Minnesota, Maryland, and Virginia. Infection with N. fowleri is most common during July, August, and September when water temperatures rise. N. fowleri grows best in water above 115°F (46°C). Consecutive hot days cause higher water temperatures, decreased water levels, and an increased number of people that engage in freshwater activities. There have only been 151 cases of PAM in the US since 1962. Of these infections, 85% were in children and adolescents, and over 75% in males (with a median age of 14 years; CDC, 2021b; Florida Health, 2021b; Gharpure et al., 2021; Minnesota Department of Health, 2018).  

The trophozoite state (the feeding stage of a protozoan parasite) is relatively sensitive to environmental changes, including temperature, while the cysts are much more tolerant to changes in their environment. The trophozoites are killed quickly by cooler temperatures for even short periods, but the cysts can survive the cold for weeks to months. This provides an opportunity for the amoeba to be found in almost any lake or river and eliminates all methods of controlling the natural levels of this parasite. The only thing that appears to make the cysts nonviable is drying them out. Chlorine and chloramine kill N. fowleri trophozoites and cysts. The amoeba does not survive in saltwater and has not been detected in the ocean (CDC, 2021b). 


Unfortunately, almost all cases of PAM end in death within five days of the appearance of symptoms. The mean time from the onset of symptoms to death is 5.3 days, with a range of 1-12 days. The mean time from exposure to death is 9.9 days, with a range of 6-17 days. Out of the 151 cases seen in the US, 147 were fatal. There have only been five documented survivors in North America: one in 1978 in the US, one in 2003 in Mexico, two in 2013 in the US, and one in 2016 in the US. Laboratory testing indicated that the original survivor in 1978 was exposed to a less virulent strain of N. fowleri than the strains encountered in this century (CDC, 2021b; Pana et al., 2022).  

Signs and Symptoms  

A patient exposed to N. fowleri presents with symptoms of PAM within 1-9 days. Early symptoms include severe headache, fever, nausea, and vomiting. Later symptoms include a stiff neck, confusion, loss of balance, photophobia, seizures, hallucinations, and cranial nerve deficits. Focal deficits and meningeal signs are typically present upon examination, and occasionally nasal discharge, nasal obstruction, and smell and taste abnormalities are present. The signs and symptoms of PAM can mimic acute bacterial meningitis, especially in the early stage. Disease progression is swift, leading to coma and eventually death. Once an autopsy is performed, the findings often include hemorrhagic necrosis of the olfactory bulbs (explaining the smell and taste abnormalities) and cerebral cortex (CDC, 2017; Minnesota Department of Health, 2018; Pana et al., 2022).  


To diagnose PAM, cerebrospinal fluid (CSF) must be obtained with a lumbar puncture. If N. fowleri is visualized in the fresh, unfrozen, unrefrigerated CSF sample under a microscope, a diagnosis of PAM is confirmed. Since the amoeba cannot tolerate cold temperatures freezing or refrigerating the sample will kill it. Diagnosis can also be made by examining tissue from a brain biopsy or autopsy specimen. Indirect immunofluorescent antibody (IFA) testing can measure serum antibody titers in a patient, but most patients do not survive long enough for an immune response to occur. Serology testing is still only considered a research technique and has not been evaluated for use as a routine diagnostic tool. The CDC requests that specimens with fresh CSF, tissue obtained from the brain, or formalin-fixed and paraffin-embedded tissue be sent to them for diagnostic confirmation (CDC, 2021b; Pana et al., 2022). 


The optimal treatment of PAM is unknown due to the high mortality rate. Current treatment recommendations are based on the regimens used in the few cases of survivors and include:  

  • amphotericin B (AmBisome), 1.5 mg/kg/day IV in 2 divided doses for three days, then 1 mg/kg/day IV once daily for 11 days 

  • intrathecal amphotericin B (AmBisome) 1.5 mg once daily for two days, then 1 mg/day every other day for eight days 

  • azithromycin (Zithromax) 10 mg/kg/day IV or PO daily for 28 days 

  • fluconazole (Diflucan) 10 mg/kg/day IV or PO daily for 28 days 

  • rifampin (Rifadin, Rimactane) 10 mg/kg/day IV or PO daily for 28 days  

  • miltefosine (Impavido) 50 mg PO twice daily for patients with a weight less than 45 kg or 50 mg PO three times daily for patients with a weight over 45 kg with a maximum dose of 2.5 mg/kg/day for 28 days  

    • miltefosine (Impavido) is an antiparasitic that is mildly nephrotoxic, so dosing should be adjusted for individuals with renal conditions; however, there is an increased risk of mortality with reduced doses, so the risk of nephrotoxicity should be balanced with the risk of dose reduction when deciding on treatment 

  • dexamethasone (Decadron) 0.6 mg/kg/day IV in four divided doses for 4 days (CDC, 2019b)  

The CDC suggests that any HCP caring for a patient with suspected PAM or other amoeba infection contact the CDC Emergency Operations Center at 770-488-7100 to consult with experts in managing these patients, including diagnostic assistance, specimen collection guidance, shipping instructions, and treatment recommendations (CDC, 2019b).  


The only way to eliminate the risk of exposure to N. fowleri and prevent PAM is to not participate in freshwater activities and never put possibly contaminated tap water into the nasal passageway (e.g., using tap water for nasal irrigation). Since this is not always possible, nurses can educate patients on prevention strategies to protect them from N. fowleri (Minnesota Department of Health, 2018; NCDHHS, 2019). Patient education should include the following information regarding taking part in water-related activities in bodies of warm freshwater: 

  • avoid entering the water if the water temperature is high and the water level is low 

  • avoid submerging your head underwater 

  • pinch your nose shut or use nose clips to keep it closed while in the water 

  • avoid activities that can stir up sediment from the bottom of the water source (Florida Health, 2021b; Minnesota Department of Health, 2018; NCDHHS, 2019)  

Patient education on safely using water for nasal irrigation should include:  

  • boil tap water for at least one minute (three minutes if at an elevation above 6,500 ft.) and let cool before use 

  • filter the water using a filter with a pore size of less than 1 micron and designed to remove aquatic toxins 

  • use only distilled or sterile water 

  • rinse all devices used with safe water (distilled, sterile, filtered, or boiled) and allow them to air dry completely (Florida Health, 2021b; Minnesota Department of Health, 2018) 

Algal Blooms  

Algae are organisms that live in aquatic environments (both freshwater and saltwater) and produce energy through photosynthesis, just like plants. Algae naturally help to sustain marine life as part of the food chain. However, when the conditions are right, microscopic algae can grow unconstrained and over-populate. The optimal conditions for this extreme growth are warm water and increased nutrients from fertilizers or sewage introduced into the water through runoff. Increased temperatures cause significantly more algae blooms. Other parameters such as salinity, water flow, rainfall, wind speed, and wind direction can impact how the bloom increases in size, where it forms, and how it moves to expose humans and animals. Evidence suggests that increased carbon dioxide (CO2) and reduced water pH can exacerbate blooms and increase their toxicity. As a result, algal blooms and their associated health and environmental impacts are a growing concern. When overgrowth occurs, the algae form a foam or scum-like mass known as an algal bloom. Wind, waves, currents, or tides can move these blooms around. They release toxins into the ecosystem, making people and animals sick. When this occurs, the algae bloom is known as a harmful algae bloom (HAB; Florida Health, 2021a; National Institute of Environmental Health Sciences [NIEHS], 2021; Stauffer et al., 2019; US Environmental Protection Agency [EPA], 2022). 

In most cases, HABs are short-lived, occur in late summer to early fall along the coast of a body of water, and vary in size and severity. Some HABs emit a foul odor due to the hydrogen sulfide gas from decomposition within the bloom. The smell is compared to rotten eggs, causing most people to avoid it whenever possible. People can get sick from HABs by eating contaminated fish, swimming, or drinking contaminated water. Unfortunately, cooking contaminated fish does not destroy the toxin, and boiling contaminated water only concentrates the toxin (Florida Health, 2021a; NIEHS, 2021). 


In fresh bodies of water, HABs are typically caused by cyanobacteria (also known as blue-green algae). This type of algae is a single-celled organism known as phytoplankton. Some cyanobacteria produce toxins called cyanotoxins. These toxins are either released from the cell during cell death or lysis or continuously released into the water without cell death. The blue-green algae blooms are primarily blue, bright green, brown, or red and have an odor like rotting plants. Pets can become sick from exposure and should be kept away from contaminated fish or water (CDC, n.d., 2022; EPA, 2021).  

Exposure to the toxins produced by cyanobacteria occurs through three routes: skin contact, inhalation, or ingestion. The toxins mix with water droplets and spray and become aerosolized, allowing humans and animals to inhale them. Ingestion can occur through eating or drinking water or food that is contaminated. It is more difficult for the toxins to pass through the skin; however, skin exposure can cause topical irritation or rashes after swimming or bathing in contaminated water. The irritation's extent depends on exposure length (CDC, 2022; EPA, 2021). Table 1 shows the side effects of specific cyanotoxins.  

Many people will present with coughing and eye irritation near the HAB, and symptoms may subside upon leaving the area. In addition to the specific type of cyanotoxin exposure, increased exposure time and comorbidities of the patient lead to more severe symptoms (CDC, 2022).  


Early identification of patient exposure to a HAB can aid the HCP in the diagnosis and guidance for potential treatment. Other illnesses with similar symptoms (i.e., organophosphate poisoning, mushroom poisoning, drug overdose, chemical burn, and acetaminophen toxicity) should be ruled out to ensure an accurate diagnosis. There are no specific diagnostic tests for cyanobacteria (CDC, n.d.). Laboratory tests that may be performed to aid in the diagnosis, along with patient history, include: 

  • electrolytes and liver function tests: BMP, ALT, AST 

  • renal function tests: BUN and creatinine 

  • serum glucose 

  • urine to check for proteinuria and glycosuria (severe toxicity) 

  • chest x-ray in patients presenting with respiratory symptoms (CDC, n.d.) 

Specialized laboratories can perform confirmatory lab tests for cyanobacteria and cyanotoxins in feces, urine, gastrointestinal contents, tissues, blood, and water specimens (CDC, n.d.).  


There is no antidote for cyanobacterial toxins. Treatment is primarily supportive and focuses on symptom management. The type of treatment used is dependent on the route of exposure. Treatment for respiratory symptoms following inhalation often includes using antihistamines and steroids. If there are no contraindications and the patient seeks professional help within 1-2 hours of ingestion, the patient can be treated with activated charcoal. If gastrointestinal symptoms appear, antiemetic or anti-diarrheal medications can be used to control nausea, vomiting, and diarrhea. Intravenous fluid administration may be needed to replace lost fluids and electrolytes. Following eye exposure, contact lenses must be removed and the eyes irrigated for at least 15 minutes with normal saline. Follow-up with an ophthalmologist is suggested if symptoms persist after irrigation. After skin exposure, contaminated clothing and jewelry should be removed, and the skin washed with soap and water for 10-15 minutes. Topical antihistamines can be used for cutaneous reactions (CDC, n.d.). 

Patient Education  

Patient education related to cyanobacteria exposure should include the following: 

  • avoid HAB contaminated waters; check local swimming and fishing advisories before visiting lakes and rivers 

  • stay out of the water if it has a foul odor; appears discolored; has foam, scum, or paint stroke-like lines on the surface; has multiple dead fish or animals along the shoreline  

  • do not boil water that contains cyanobacteria toxins 

  • do not fill pools with water from a lake, river, or pond 

  • avoid eating large reef fish (e.g., grouper) – especially the head, gut, liver, or eggs 

  • when fishing or collecting shellfish for consumption, check local shellfish and fish advisories before ingesting the seafood  

  • following exposure to contaminated waters, wash exposed areas with soap and water, follow up with an HCP, call the poison control center hotline, and report the illness to the local and state health departments  

  • pets who have been exposed to toxins from drinking contaminated water or eating contaminated marine animals require prompt veterinarian treatment as they can become very sick quickly (CDC, 2021c; Florida Health, 2021a) 

Red Tide 

Like freshwater HABs, those found in saltwater are caused by phytoplankton, most commonly diatoms and dinoflagellates. Saltwater HABs are known as red tides. The most common type in the US is Karenia brevis blooms which appear dark red or brown and occur most frequently in the Gulf of Mexico. The toxin produced by Karenia brevis is brevetoxin, a tasteless, odorless neurotoxic compound that can cause toxicity through inhalation, ingestion, or dermal exposure. The most common transmission route of Karenia brevis is through contaminated shellfish; however, patients can also be exposed to the red tide algae blooms through exposure to the contaminated water (CDC, 2021a; Florida Health, 2021a). 


Exposure to the HAB can induce red tide tickle, an illness characterized by a scratchy throat and cough secondary to breathing in airborne brevetoxins. These toxins are released into the air when the wind or waves break open the algae cells. Healthy individuals can develop respiratory symptoms rapidly after exposure to HAB. In addition to red tide tickle, other respiratory symptoms have been reported, including shortness of breath, sneezing, eye irritation, and nasal irritation. Exposure to brevetoxins can induce an acute exacerbation for those with chronic respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), or emphysema. Illness from ingesting the toxin by eating contaminated fish or shellfish is characterized by gastrointestinal and neurological symptoms, including abdominal pain, nausea, vomiting, diarrhea, tingling of the mouth and tongue, vertigo, ataxia, reversal of temperature perception, and slurred speech. In severe cases, neurological symptoms can progress to partial paralysis (CDC, 2021a; Florida Health, 2021a). 


Symptomatic evaluation with a history of potential patient exposure to brevetoxin can aid the HCP in determining the diagnosis. Laboratory verification can be achieved by detecting brevotoxins or their metabolites in a urine specimen through immunoassay (CDC, 2018). 


Following physical contact with brevetoxins, it is advised to wash the contaminated area with soap and water immediately. For rashes or skin irritation, a topical steroid such as hydrocortisone (Dermacort) cream may be used to decrease the symptoms. Those with persistent respiratory symptoms can be advised to take over-the-counter antihistamines. For more severe or persistent symptoms, patients should be evaluated and treated with systemic steroids, bronchodilators, oxygen, or other supportive therapy to ensure the patency of the airway (Florida Health, 2021a). 

Protection from Aquatic Toxins 

The HCP can offer education to avoid exposure to toxins within waterways in the local environment. The primary way to prevent exposure to aquatic toxins is to avoid fresh and saltwater where algal blooms are present. Pets should also be protected and kept away from contaminated water. If exposure occurs, they should not be allowed to lick their fur until the toxin is washed out with soap and water. When visiting state or local waterways, patients should be encouraged to review official health department reports and adhere to any warnings or local conditions that would direct activities in the water. If there is a notification of harmful algae in the public drinking water supply, all local or state guidelines should be followed to minimize risks. Finally, patients should avoid eating any seafood that may be contaminated by HABs and their toxins (CDC, 2019a, 2021b).  

The CDC reports that people can be exposed to HAB toxins up to four miles inland from a contaminated water source. Since marine HAB can cover hundreds of square miles, the toxins can impact boaters, homeowners, residents, and tourists. Unfortunately, the only way to avoid exposure is to stay out of the affected area. This can be difficult for those who work or live in the area. For aerosolized toxins, the use of particle filter masks when outdoors can decrease exposure. For those who live near the HAB, remaining indoors using air-conditioning instead of having windows open can reduce the severity of respiratory symptoms. Ingestion can be prevented by avoiding raw seafood, especially oysters and other shellfish. Not only can shellfish and marine animals living directly in the HAB be contaminated by the toxins, but larger fish or animals that feed on these fish may be exposed. Fish tested following exposure to blue-green algae have demonstrated that there is not a high accumulation of cyanotoxins in the edible parts, but there may be a high level in the organs (CDC, 2019a, 2021b; Florida Health, 2021a). 

Tap water can contain HAB toxins, but this is uncommon, even in areas with high levels of toxins. There are currently no federal guidelines regarding acceptable levels of cyanobacteria or cyanotoxins in public drinking water. Exposure can also occur through healthcare facilities, but this risk remains very low. Nutritional supplements that contain algae could pose a risk for exposure to HAB toxins. During algae harvesting to produce supplements, toxin-producing cyanobacteria could accidentally be included, leading to contamination (CDC, 2019a).  

Preventing Algal Blooms from Forming 

As with all health concerns, prevention is preferred over treatment. There are large-scale efforts across the US to reduce the incidence of HABs, primarily by decreasing the amount of nitrogen and phosphorus polluting our waterways (National Oceanic and Atmospheric Administration [NOAA], 2021). Suggestions to support these initiatives include (NOAA, 2021): 

  • Use only recommended quantities of fertilizer on individual lawns to reduce the runoff going into local waterways providing algae the nutrients needed to flourish. 

  • Maintain septic systems to prevent wastewater leakage into nearby waterways, as wastewater is a rich source of nutrients for algae. 




Centers for Disease Control and Prevention. (n.d.). Facts about cyanobacterial harmful algal blooms for poison center professionals. Retrieved June 24, 2022, from https://www.cdc.gov/nceh/hsb/chemicals/pdfs/Facts_Cyanobacterial_Harmful_Algal_Blooms_508.pdf 

Centers for Disease Control and Prevention. (2017). Pathogen & environment [Image]. https://www.cdc.gov/parasites/naegleria/pathogen.html 

Centers for Disease Control and Prevention. (2018). Case definition: Brevetoxin. https://emergency.cdc.gov/agent/brevetoxin/casedef.asp 

Centers for Disease Control and Prevention. (2019a). Prevention tips. https://www.cdc.gov/vibrio/prevention.html 

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Centers for Disease Control and Prevention. (2021c). Protect yourself and your pets. https://www.cdc.gov/habs/prevention-control.html 

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