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Fact Sheet: Blue-Green Algae/Cyanobacteria Harmful Algal Bloom (HABs) Physician Reference

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Blue-Green Algae/Cyanobacteria Harmful Algal Bloom (HABs) Physician Reference

From the Ohio Department of Health Bureau of Environmental Health – Health Assessment Section – “To protect and improve the health of all Ohioans”


The Public Health Issue:

This summer Ohio’s local health departments, local physician offices, Poison Control Centers and the state health department have received reports of illness from people who have claimed to have had contact with HAB-contaminated water. Several of Ohio’s inland lakes have experienced cyanobacteria blue-green algae blooms, commonly referred to as Harmful Algal Blooms (HABs). Depending on the genera, water conditions, and other factors, neurotoxins, hepatotoxins, cytotoxins, dermatotoxins and gastrointestinal toxins can be produced by cyanobacteria. These toxins are released to the water as the bacteria die. Water samples from various Ohio lakes have detected the presence of microcystin, anatoxin-a, cylindrospermopsin and saxitoxin. Both humans and animals can experience illness from exposure to these toxins during recreational activities and other water uses.


Exposure and Clinical Presentation:

Route of Exposure Symptoms/Signs Time to symptom onset* Differential Diagnosis
Swallowing water contaminated with cyanobacteria or toxins Hepatotoxins
(microcystins, cylindrospermopsin)
Elevated ALT, GGT
Acute hepatitis
Kidney damage
Minutes to hours Other hepatotoxin poisoning,
other microbial infections/toxins
Swallowing water  contaminated with cyanobacteria or toxins Neurotoxins
(anatoxin-a, anatoxin-a[s], saxitoxin)
Motor weakness
Respiratory & muscular
Minutes to hours Pesticide poisoning, other toxin
Skin contact with water contaminated with cyanobacteria or toxins
or contact with animals contaminated with
Dermal toxins
(Lyngbyatoxins, lipopolysaccharide
Rash, hives
Skin blistering
Allergic reactions
Minutes to hours Other dermal allergens.
non-allergic urticaria,
photosensitivity reactions
Inhaling aerosolized droplets contaminated with cyanobacteria or toxins Upper respiratory irritation
Possibe allergic reaction
Unknown, but likely an acute reaction Other airborne allergens, upper
respiratory infection, flu
*Symptom onset times are primarily extrapolations from laboratory animal data and events.


Diagnosis and Lab Testing:

Currently there is no laboratory diagnostic testing which can confirm the presence of cyanotoxins in human clinical specimens. In the absence of laboratory confirmation, presumptive diagnosis can be made based upon exposure history, clinical signs and symptoms, and ruling out other diagnoses. In cases where exposure to hepatotoxins is suspected, a standard liver panel is recommended (AST (SGOT), ALT, ALP, GGT, albumin and bilirubin). Tests for ruling out other diagnoses should also be performed.


Case Definition

CDC case definition summary for selected toxins (for complete description see CDC Proposed Case Definitions for Algal Toxin-related Diseases)

  • Suspect Case Exposure to water with a confirmed algal bloom AND onset of associated signs and symptoms within a reasonable time after exposure AND without identification of another cause of illness.
  • Probable Case Meets criteria for Suspect Case AND there is laboratory documentation of a HAB toxin(s) in the water.
  • Confirmed Case Meets criteria for a Probable Case combined with professional judgment based on medical review.
Type of Toxin Causative organism Vector
Anatoxin-a Neurotoxin Anabaena spp.
Aphanizomenon spp.
Planktothrix spp.
fresh water
Anatoxin-a(s) Neurotoxin Anabaena flos-aquae Contaminated
fresh water
Cylindrospermopsin Hepatotoxin Cylindrospermopsis
raciborskii, Aphanizomenon
Contaminated fresh water and
possibly fish
Lyngbyatoxin Dermal toxin Lyngbya spp. Contaminated
fresh or marine waters
Microcystins Hepatotoxin M. aeruginosa
Anabaena spp.
Planktothrix spp.
fresh water
Saxitoxins Neurotoxin Anabaena circinalis
Lyngbya wollei
Contaminated fresh water


Treatment and Patient Management:

Symptomatic, supportive care. There are currently no known antidotes for exposures to the group of toxins associated with cyanobacteria. Follow-up laboratory testing as indicated.


Patient Education

Community education outreach efforts are currently being pursued by the state agencies involved addressing Ohio HABs. Please refer to the following links for more information regarding Harmful Algal Blooms:


HAB Case Reporting Requirements

Pursuant to Ohio Administrative Code (OAC) Chapter 3701-3-02 and the ODH Infectious Disease Control Manual healthcare providers are required to submit reports of human illness related to exposure to HABs to the local health district where the ill individual resides. Reports are to be made under Class C – “waterborne disease outbreaks; report single cases of toxin poisoning associated with exposure to water with a confirmed algal bloom by the end of the next business day to the local public health department where the patient resides.”

WHO must report? Healthcare providers (physicians, hospitals, infection control professionals, local public health providers) with knowledge of a case or suspect case of HAB exposure and illness are required to report.
WHAT must be reported? Healthcare providers must submit the HAB-related human illness form to the local health district where the ill individual resides.
WHEN must a report be made? Class C – must be sent by the end of the next business day to the local public health department where the patient resides.
WHERE must the report be made? Healthcare providers should send the case information the local health jurisdiction in which the case or suspected case was believed to take place.
A listing of local health departments may be found at:

ODH, with assistance from the Centers for Disease Control and Prevention, has developed case definitions and the following human illness reporting form for HAB-related illnesses:


HAB-related human illness report:


Animal Illness:
Reports of suspected domestic animal illness associated with exposure to HAB should be reported to the Local Health District. Local health districts receiving reports from veterinarians should contact the ODH Zoonotic Disease Program (ZDP) at 614-752-1029, select option two (2). Completed animal illness report forms can be faxed to the ODH ZDP at 614-644-1057.


HAB-related animal illness report:


Additional Resources:

Centers for Disease Control and Prevention
Harmful Algal Blooms
CDC, Environmental Hazards & Health Effects, Harmful Algal Blooms (HABs)
Other publications, data and statistics


Cyanobacteria and cyanotoxins in drinking-water
Toxicological Reviews of Cyanobacterial Toxins: Microcystins LR, RR, YR and LA (External Review Draft) 


World Health Organization
Toxic cyanobacteria in water: A guide to their public health consequences, monitoring and management


Global Water Research Coalition – Water Quality Research of Australia
International Guidance Manual for the Management of Toxic Cyanobacteria


Canadian Drinking Water Guidance
Federal-Provincial-Territorial Committee on Drinking Water


Where can I get more Information?

Ohio Department of Health
Bureau of Environmental Health
246 N. High Street
Columbus, Ohio 43215
Phone: (614) 466-1390
Fax: (614) 466-4556


Download a printable version of this fact sheet here.


250 William Howard Taft Road
2nd Floor, Cincinnati, OH 45219
Phone 513.946.7800 Fax 513.946.7890