Occurrence of Aeromonas spp. in a random sample of drinking water distribution systems in the USA.

Aeromonads are aquatic bacteria found in drinking water supplies worldwide. Some species, such as Aeromonas hydrophila, can cause disease in humans. For this survey, 293 United States public water systems were selected using random sampling, stratified by water source and system type. Water samples were collected during one year from three sites (six samples per site) in each system. Temperature, pH, turbidity, total and free chlorine were measured using standard methods. Aeromonads were detected in 130 of 5,042 valid samples (2.6%) from 42 (14.3%) systems using the ampicillin-dextrin agar with vancomycin culture method with oxidase, trehalose and indole confirmation tests. Concentrations of aeromonads in positive samples were 0.2 to 880 (median 1.6) colony-forming units (CFU) per 100 mL. Adjusted odds ratios of Aeromonas detection were 1.6 (95% confidence limits 1.0, 2.5) during the summer season, 3.3 (1.8, 6.2) for turbidity above 0.5 nephelometric units and 9.1 (3.5, 24) at 0 mg/L compared with 0.25 mg/L total chlorine. Geographic region, system size and type of water source were not significant predictors of Aeromonas detection in multivariate regression analysis. The results of this survey demonstrate the importance of maintaining adequate residual chlorine and low turbidity for preventing drinking water contamination with aeromonads.