• Avian cercariae: avian cercariae are schistosome larvae for which humans are an accidental host. Pruritus and macules are the initial signs and symptoms; sometimes a diffuse erythema and urticaria can develop and last for several hours [96-99]. Fever, nausea and vomiting can also accompany severely affected cases [97,100]. The clinical presentation of cercarial dermatitis can be difficult to delineate from the picture of cyanobacterial dermatitis.
• Gram-negative bacteria: Aeromonas hydrophila and Chromobacterium violaceum are abundant in freshwater habitats. Both usually cause infection through a pre-existing skin wound, though the clinical presentations in each case do not match of any of the reports listed in Additional File 1. A. hydrophila causes cellulitis and a purulent discharge; aspiration of water can cause pneumonia and septicaemia. C. violaceum infections present with various cutaneous signs that are secondary to systemic disease, including sepsis [101]. Vibrio vulnificus has reportedly caused soft tissue infection after contact in brackish inland waters, though most cases are associated with estuarine contact [102]. Pseudomonas aeruginosa is widely-distributed in natural and artificial aquatic environments. Cutaneous infection presents as an erythematous or urticarial rash some 18–24 hours after water contact and progresses to a follicular dermatitis. Fever and pruritus are uncommon. Most reports of pseudomonal dermatitis are related to spa pool or hot-tub exposures [102,103]. P. aeruginosa in recreational waters is a common cause of otitis externa, presenting as a purulent discharge [102]. Diagnostic criteria include culturing the organism from skin or ear swabs; the incubation period would also help to distinguish P. aeruginosa infection from cyanobacteria-related dermatoses.
• Non-allergic urticaria: physical stimuli such as heat, cold and exercise can induce itching and hives in susceptible individuals [99,104].
Gastro-intestinal illness
• Shigellosis: Shigella outbreaks are the most commonly reported cause of disease associated with untreated inland recreational water in the USA, with 16 events affecting almost 1,300 people between 1985 and 1994 [102]. The incubation period is typically 2–3 days, with an upper limit of about 7 days. Illness severity is strain-dependent, with most S. sonnei infections being mild and self-limiting, and S. dysenteriae type 1 associated with severe diarrhoea which may progress to a life-threatening illness [102].
• Escherichia coli: E. coli are markers of faecal pollution in recreational waters. Disease outbreaks traced to enterohaemorrhagic E. coli 0157 have been reported from recreational water exposures [102,105].
• Norwalk-like viruses: Various transmission routes, including recreational water outbreaks have been documented [105].
Other microbial pathogens
• Naegleria fowleri: N. fowleri is a free-living thermotolerant amoeba found in warm or thermally polluted waters. It is the causative organism of primary amoebic meningoencephalitis, a fulminating, typically fatal illness. The entry route is via the nasal mucosa; fit, immunocompetent children and young adults with a recent history of freshwater recreational activity are those most commonly affected. The causative organism and diagnosis are usually confirmed at autopsy. Several reviews are available, e.g. [106-113].
• Viruses: Pharyngo-conjunctival fever outbreaks associated with non-enteric adenoviruses in recreational waters have been reported [105].
• Legionella: Legionella infections have been associated with recreational water contact [105].
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