Cutaneous hypersensitivity reactions to freshwater cyanobacteria – human volunteer studies

A consecutive series of adult patients presenting for diagnostic skin patch testing at a hospital outpatient clinic were invited to participate. A convenience sample of volunteers matched for age and sex was also enrolled. Patches containing aqueous suspensions of various cyanobacteria at three concentrations were applied for 48 hours; dermatological assessment was made 48 hours and 96 hours after application.20 outpatients and 19 reference subjects were recruited into the study. A single outpatient produced unequivocal reactions to several cyanobacteria suspensions; this subject was also the only one of the outpatient group with a diagnosis of atopic dermatitis. No subjects in the reference group developed clinically detectable skin reactions to cyanobacteria.This preliminary clinical study demonstrates that hypersensitivity reactions to cyanobacteria appear to be infrequent in both the general and dermatological outpatient populations. As cyanobacteria are widely distributed in aquatic environments, a better appreciation of risk factors, particularly with respect to allergic predisposition, may help to refine health advice given to people engaging in recreational activities where nuisance cyanobacteria are a problem.Cyanobacteria, commonly but erroneously known as blue-green algae, are common inhabitants of freshwater lakes and reservoirs throughout the world. Under favourable conditions certain cyanobacteria can dominate the phytoplankton within a waterbody and undergo mass developments, known as blooms. Public health concerns arise because many nuisance cyanobacteria can produce potent toxins. Anecdotal and case reports have documented skin rashes, often described as intensely pruritic, associated with contact exposure to cyanobacteria. While there are relatively few references in the scientific and medical literature since these reports began in 1949, under-diagnosis of cyanobacteria-associated illness was suggested by Schwimmer & Schwimmer [1] in 1968, a suspi