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Open Access Research article

Epidemiology of recreational exposure to freshwater cyanobacteria – an international prospective cohort study

Ian Stewart123*, Penelope M Webb4, Philip J Schluter5, Lora E Fleming6, John W Burns7, Miroslav Gantar8, Lorraine C Backer9 and Glen R Shaw1103

Author Affiliations

1 National Research Centre for Environmental Toxicology, University of Queensland, 39 Kessels Road, Coopers Plains, QLD 4108, Australia

2 School of Population Health, University of Queensland, Herston Road, Herston, QLD 4006, Australia

3 Cooperative Research Centre for Water Quality and Treatment, PMB 3, Salisbury, SA 5108, Australia

4 Queensland Institute of Medical Research, 300 Herston Road, Herston, QLD 4006, Australia

5 Faculty of Health and Environmental Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1020, New Zealand

6 NIEHS Marine & Freshwater Biomedical Sciences Center, University of Miami, FL 33149, USA

7 PBS&J, 701 San Marco Blvd., Suite 1201, Jacksonville, FL 32207–8175, USA

8 Department of Biology, Florida International University, Miami, FL 33199, USA

9 National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA

10 School of Public Health, Griffith University, University Drive, Meadowbrook, QLD 4131, Australia

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BMC Public Health 2006, 6:93  doi:10.1186/1471-2458-6-93

Published: 11 April 2006



Case studies and anecdotal reports have documented a range of acute illnesses associated with exposure to cyanobacteria and their toxins in recreational waters. The epidemiological data to date are limited; we sought to improve on the design of some previously conducted studies in order to facilitate revision and refinement of guidelines for exposure to cyanobacteria in recreational waters.


A prospective cohort study was conducted to investigate the incidence of acute symptoms in individuals exposed, through recreational activities, to low (cell surface area <2.4 mm2/mL), medium (2.4–12.0 mm2/mL) and high (>12.0 mm2/mL) levels of cyanobacteria in lakes and rivers in southeast Queensland, the central coast area of New South Wales, and northeast and central Florida. Multivariable logistic regression analyses were employed; models adjusted for region, age, smoking, prior history of asthma, hay fever or skin disease (eczema or dermatitis) and clustering by household.


Of individuals approached, 3,595 met the eligibility criteria, 3,193 (89%) agreed to participate and 1,331 (37%) completed both the questionnaire and follow-up interview. Respiratory symptoms were 2.1 (95%CI: 1.1–4.0) times more likely to be reported by subjects exposed to high levels of cyanobacteria than by those exposed to low levels. Similarly, when grouping all reported symptoms, individuals exposed to high levels of cyanobacteria were 1.7 (95%CI: 1.0–2.8) times more likely to report symptoms than their low-level cyanobacteria-exposed counterparts.


A significant increase in reporting of minor self-limiting symptoms, particularly respiratory symptoms, was associated with exposure to higher levels of cyanobacteria of mixed genera. We suggest that exposure to cyanobacteria based on total cell surface area above 12 mm2/mL could result in increased incidence of symptoms. The potential for severe, life-threatening cyanobacteria-related illness is likely to be greater in recreational waters that have significant levels of cyanobacterial toxins, so future epidemiological investigations should be directed towards recreational exposure to cyanotoxins.