Atmospheric dispersion and transmission of Legionella from wastewater treatment plants: A 6-year case-control study.

Legionnaires Disease incidence has risen in the Netherlands in recent years. For the majority of the cases, the source of infection is never identified. Two Dutch wastewater treatment plants (WWTPs) have previously been identified as source of outbreaks of Legionnaires Disease (LD) among local residents. The objective of this study is to examine if LD patients in the Netherlands are more exposed to aerosols originating from WWTPs than controls. METHODS: An atmospheric dispersion model was used to generate nationwide exposure maps of aerosols from 776 WWTPs in the Netherlands. Municipal sewage treatment plants and industrial WWTPs were both included. Exposure of LD cases and controls at the residential address was compared, in a matched case-control design using a conditional logistic regression. Cases were notified LD cases with onset of disease in the period 2013-2018 in the Netherlands (n = 1604). RESULTS: Aerosols dispersed over a large part of the Netherlands, but modelled concentrations are estimated to be elevated in close proximity to WWTPs. A statistically significant association was found between LD and the calculated annual average aerosol concentrations originating from WWTPs (odds-ratio: 1.32 (1.06-1.63)). This association remained significant when the two outbreak-related WWTPs were removed from the analysis (odds-ratio: 1.28 (1.03-1.58)). CONCLUSION: LD cases were more exposed to aerosols from WWTPs than controls. This indicates that exposure to aerosols dispersed from WWTPs caused Legionnaires Disease in residents living near WWTPs in the period 2013-2018. In order to investigate which characteristics of WWTPs are associated with an increased LD risk, the WWTP database should be updated and more data is needed on the presence and survival of aerosolized Legionella bacteria to improve the Legionella dispersion modelling. Furthermore, it is recommended to further investigate how aerosol dispersion of WWTPs can effectively be reduced in order to reduce the potential health risk.

[Mapping HIV prevalence in the Netherlands with geographic information systems]. / Hiv-bestrijding begint met GIS-werk.

OBJECTIVE: To map regions of the Netherlands with high HIV prevalence for surveillance and prevention purposes. METHOD: Information on numbers of HIV patients receiving clinical care on 31 December 2014 per postcode region was requested from the HIV monitoring foundation (SHM). These details were related to data from Statistics Netherlands on the number of residents per municipal area or district with the aid of a geographic information system (GIS). RESULTS: Distribution mapping showed that ten municipal areas in the Netherlands have an HIV prevalence of 2 or more per 1000 residents aged 15-60 years. We discovered the highest prevalence in Amsterdam (8.1) and suburbs, Rotterdam (3.4), The Hague (2.7) and Arnhem (2.5). Large differences were seen between districts, particularly in Amsterdam where HIV was concentrated within two districts: Central Amsterdam (9-28) and Amsterdam Southeast (5-20). In Rotterdam and The Hague, HIV prevalence rates are lower and differences between districts are smaller. CONCLUSION: Geographical analyses show differences in HIV prevalence for municipal areas and districts in big cities in the Netherlands. These data can be used for new interventions, to better focus HIV detection.