Microbial content of drinking water in Finnish and Russian Karelia – implications for atopy prevalence

Background and aim:  The influence of microbial quality of drinking water from different sources on the occurrence of atopy has been poorly examined. This study was undertaken to clarify the association between the overall microbial content in drinking water and the occurrence of atopy among schoolchildren from two neighbouring areas with profound differences in living conditions and lifestyles. Methods:  Drinking water samples were obtained from kitchens of nine schools in North Karelia, Finland and of nine schools from Pitkäranta, the Republic of Karelia, Russia. The pupils of these schools were participants of the Karelian Allergy Study. Occurrence of atopy, determined by skin prick test positivity (one or more) to 14 common airborne and food allergens, was measured in all 563 children, aged 7–16 years, from these 18 schools. Water samples were analysed using standard methods for drinking water analyses including viable counts for Escherichia coli , intestinal enterococci, coliform bacteria and heterotrophic bacteria. In addition, total cell counts including both viable and nonviable bacteria, algae and protozoans were assessed using epifluorescence microscope with 4′‐6‐diamidino‐2‐phenylindole (DAPI) staining. Results:  In Finland, 29% of the children were sensitized to birch when compared with 2% of the Russian children ( P  < 0.0001). Overall, sensitization rates for any of the pollens were 39% and 8% ( P  < 0.0001), and for any of the allergens 48% and 16%, respectively ( P  < 0.0001). Because of substantial differences in raw water sources and treatment practices, the total numbers of microbial cells in drinking water were many‐fold higher in Russia than in Finland. A dose–response relationship was found for occurrence of atopy and the DAPI value indicative of microbial cell content in the water ( P  < 0.0001). Further, multivariate logistic regression analysis revealed that high (>10 6  cells/ml) and intermediate (10 5 –10 6  cells/ml) DAPI values were associated with reduced risk of atopy (odds ratio 0.34, 95% confidence interval 0.20–0.57 and 0.39, 0.23–0.69, respectively), independently from other factors. Conclusion:  High overall content of micro‐organisms in drinking water may be associated with reduced risk of atopy, independently from other determinants.