Prospective study of acute health effects in relation to exposure to cyanobacteria

We conducted a study to investigate the relationship between exposure to cyanobacteria and microcystins and the incidence of symptoms in humans living in close proximity to lakes affected by cyanobacteria. The design was a prospective study of residents living around three lakes (Canada), one of which has a water treatment plant supplying potable water to local residents. Participants had to keep a daily journal of symptoms and record contact (full or limited) with the water body. Samples were collected to document cyanobacteria and microcystin concentrations. Symptoms potentially associated with cyanobacteria (gastrointestinal: 2 indices (GI1: diarrhea or abdominal pain or nausea or vomiting; GI2: diarrhea or vomiting or [nausea and fever] or [abdominal cramps and fever]); upper and lower respiratory tract; eye; ear; skin; muscle pain; headaches; mouth ulcers) were examined in relation with exposure to cyanobacteria and microcystin by using Poisson regression. Only gastrointestinal symptoms were associated with recreational contact. Globally, there was a significant increase in adjusted relative risk (RR) with higher cyanobacterial cell counts for GI2 (< 20,000 cells/mL: RR = 1.52, 95% CI = 0.65-3.51; 20,000-100,000 cells/mL: RR = 2.71, 95% CI = 1.02-7.16; > 100,000 cells/mL: RR = 3.28, 95% CI = 1.69-6.37, p-trend = 0.001). In participants who received their drinking water supply from a plant whose source was contaminated by cyanobacteria, an increase in muscle pain (RR = 5.16; 95% CI = 2.93-9.07) and gastrointestinal (GI1: RR = 3.87; 95% CI = 1.62-9.21; GI2: RR = 2.84; 95% CI = 0.82-9.79), skin (RR = 2.65; 95% CI = 1.09-6.44) and ear symptoms (RR = 6.10; 95% CI = 2.48-15.03) was observed. The population should be made aware of the risks of gastrointestinal symptoms associated with contact (full or limited) with cyanobacteria. A risk management plan is needed for water treatment plants that draw their water from a source contaminated with cyanobacteria.