Use of surface water in drinking water production associated with municipal Legionnaires’ disease incidence

Abstract

Study objectives: Given an observed geographical variation in Legionnaires’ disease incidence in The Netherlands, the aim of the study was to test the hypothesis that the type of drinking water production was an independent determinant of the incidence of Legionnaires’ disease.

Design: For the 1987–2005 period, the incidence of Legionnaires’ disease in The Netherlands and the price of water as a proxy for production type was studied at the municipal level. The data on the price of water were available at the municipal level.

Methods: For each of the 466 municipalities in The Netherlands a mean standardised incidence rate per 100 000 inhabitants over the 1987–2005 period was calculated, excluding patients with the most probable source of infection abroad or in hospital. Logistic regression was used to assess the relation of the price of water to the incidence rates. In order to control for diagnostic and inclusion bias, they were estimated using questionnaire data collected from all 62 medical microbiology laboratories in the country.

Main results: The incidence of Legionnaires’ disease varied between municipalities from 0.0 to 5.6 per 100 000 person-years. In univariate analysis high versus low water price was positively associated with a high municipal incidence rate (odds ratio (OR) 1.9; 95% CI 1.5–2.6). The association persisted (OR 5.1; 95% CI 3.2–8.0) after correction for diagnostic and inclusion bias.

Conclusions: The price of water as a proxy for the type of water production was an independent risk factor for high municipal Legionnaires’ disease incidence in The Netherlands. This can guide future prevention policies.