Sampling and identification of Legionella spp. at Borregaard Ind. Ltd.

During May 2005, 56 inhabitants of Sarpsborg/Fredrikstad developed legionellosis caused by Legionella pneumophila serogroup 1, resulting in the death of ten patients. The wet scrubber at Borregaard Ind. Ltd. was identified as the source, In November 2005, three new cases of legionellosis were reported in Sarpsborg/Fredrikstad, but the source for exposure has still not been identified. There are very few studies elaborating the dispersion pattern and the impact of atmospheric conditions on the transmission of Legionella in air. This study has focused on the sampling of aerosols containing L. pneumophila and identifying this bacterial species by molecular methods. Also, one of the goals of this project was to elaborate the dispersion of L. pneumophila from the aeration ponds at Borregaard’s biological treatment plants to ambient air. This project was initiated by Borregaard Ind. Ltd. and involved three collaborating partners; The Norwegian Defence Research Establishment (Forsvarets forskningsinstitutt FFI), the Norwegian Institute of Public Health and Telelab AS. The project owner is Borregaard Ind. Ltd and FFI has been the project coordinator. The work was carried out during 13.06.2006 – 05.12.2006. This report describes the work performed by FFI. The dispersion of Legionella was studied by sampling airborne aerosols above and around the aeration ponds according to selected regions well suited for the aerosol sampling by predictions made by a Computational Fluid Dynamic (CFD) model of the biological treatment plant. The air collector SASS 2000PLUS was suitable for sampling aerosols containing viable Legionella cells and L. pneumophila was identified by specific real-time PCR using the mip primers. Results showed that L. pneumophila was, in general, not identified upwind of the aeration ponds. L. pneumophila was identified up to 180 m downwind of the aeration pond, strongly indicating that the aeration ponds are a source for generating aerosols of L. pneumophila. L. pneumophila was identified by mip real-time PCR in liquid samples harvested from all three aeration ponds at Borregaard Ind. Ltd., and from the Glomma river. It is not known if these air and liquid samples contain the same L. pneumophila strain, and if this strain is pathogenic to humans. Several different bacterial genus and species were identified in the aeration ponds by molecular and microbiological analysis. Pseudomonas spp., Acinetobacter spp., Vibrio spp. Shewanella spp., Enterococcus spp. and several other bacteria commonly found in the environment were identified in the aeration ponds. Some of these bacterial species are opportunistic human pathogens suggesting that care should be taken when working close to these ponds. An overall presentation of the work performed from all collaborating partners has been published in the FFI report 2007/00560.