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Swimming pool-related Pseudomonas aeruginosa infections mainly result in folliculitis and otitis externa. P. aeruginosa forms biofilms on surfaces in the swimming pool environment. The presence of P. aeruginosa on inflatables and foam teaching aids in 24 public swimming pools in the Netherlands was studied. Samples (n = 230) were taken from 175 objects and analysed for P. aeruginosa by culture. Isolated P. aeruginosa were tested for antibiotic resistance by disk diffusion. P. aeruginosa was detected in 63 samples (27%), from 47 objects (27%) in 19 (79%) swimming pools. More vinyl-canvas objects (44%) than foam objects (20%) were contaminated, as were wet objects (43%) compared to dry objects (13%). Concentrations were variable, and on average higher on vinyl-canvas than on foam objects. Forty of 193 (21%) P. aeruginosa isolates from 11 different objects were (intermediate) resistant to one or more of 12 clinically relevant antibiotics, mostly to imipenem and aztreonam. The immediate risk of a P. aeruginosa infection from exposure to swimming pool objects seems limited, but the presence of P. aeruginosa on pool objects is unwanted and requires attention of pool managers and responsible authorities. Strict drying and cleaning policies are needed for infrequently used vinyl-canvas objects.

The use of roof-collected rainwater as a freely available and sustainable alternative to drinking water produced by drinking water companies increases worldwide. Initially, rainwater is free of microbial contamination, but it may become contaminated by animals and humans or, alternatively, human pathogens may grow in stored rainwater resulting in a significant human health risk from infectious diseases. This three-year study demonstrated that rainwater stored in different reservoirs in The Netherlands was frequently faecally contaminated and incidentally contained potential human pathogens such as Campylobacter, Cryptosporidium, Giardia, Aeromonas hydrophila and Legionella. Analysis of samples during a period with variable weather conditions showed a correlation between rainfall intensity and faecal indicator counts and increased detection of pathogens after heavy rainfall incidents. Outside temperature had a limited effect on both the temperature and the microbiological quality of the water in the reservoirs, which did not comply with Dutch drinking water legislation and should thus not be consumed without treatment. In general, a health risk may arise from exposure to pathogens when contaminated droplets are inhaled, ingested or come into contact with the skin. Health risks may be reduced by regular cleaning of the collection, storage and transport means, but to assess their efficacy field intervention studies are required.

Outbreaks of cercarial dermatitis which occurred in recreational lakes in the Netherlands were studied and a method for direct rapid detection of the parasite Trichobilharzia in water samples was developed. A standardized questionnaire with questions on health complaints and exposure was distributed to individuals who developed symptoms of cercarial dermatitis after visiting fresh water lakes. Snails from the suspected lakes were examined for the presence of Trichobilharzia by microscopy and PCR. Water samples were concentrated by filtration and examined by PCR. Water quality was tested according to European Bathing Water Directive 76/160/EEG. Trichobilharzia was detected in snails and water samples from lakes which met European bathing water standards. Despite a response of 25.5%, epidemiological data suggested that longer and more frequent exposure to the water resulted in increased reporting of symptoms of cercarial dermatitis and confirmed the importance of exposure as a risk factor. A novel method for direct detection of Trichobilharzia, which includes concentration of water samples by filtration and detection of the parasite by PCR proved to be a valuable and simple tool for confirmation of presumptive outbreaks, particularly when snails could not be found in the suspected water and public health protecting measures were necessary.

The occurrence of Cryptosporidium and Giardia in indoor swimming pools in the Netherlands was studied at five locations. The backwash water from seven pool filters was analysed for the presence of Cryptosporidium oocysts and Giardia cysts for a period of 1 year. Of the 153 samples of filter backwash water analysed, 18 (11.8%) were found positive for either Cryptosporidium (4.6%), Giardia (5.9%) or both (1.3%). Oocysts and cysts were also detected in the water of one toddler pool and one learner pool. Although most of the (oo)cysts in the filter backwash water were dead, viable and potentially infectious oocysts were detected in the learner pool. On the basis of numbers of potentially infectious (oo)cysts detected in the learner pool, and assuming one visit to an infected pool per year, risk assessment indicated an estimated risk of infection with Cryptosporidium that exceeded the generally accepted risk of one infection per 10,000 persons per year. Guidelines for pool operators on how to manage faecal accidents and public information on the importance of hygiene in swimming pool complexes are recommended tools in controlling the risk of infection.