An in-field hygiene-epidemiological demonstration of the true relations between a case of legionellosis and single spot exposure to L. pneumophila from shower on board a Norwegian seismic vessel in the Gulf of Mexico

Abstract number: 1134_01_234

Ahlén C., Aas M.

Introduction:  

Legionellosis is a life-threathening illness which to a high degree is shown to be caused by Legionella pneumophila. Most well known are the outbreaks from air condition systems, which regularly are seen from hotels and hospitals around the world. Although outbreaks connected to showers and bobble-pooles are discussed, specific demonstration of true genetical relations between infection and specific exposure have only infrequently been presented. In this paper we present a case of legionellosis, occurring on board a ship in the Gulf of Mexico, diagnosed at a hospital in Norway, epidemiologically surveyed on board and identified as being connected to one certain shower on board the ship.

Material and Methods:  

The hygiene-epidemiological surveys were done by water samplings and swabs from showers in all cabins on board (n = 39). In addition, swabs were taken from each of the shower hoses and taps giving a total number of samples of 136. The samplings were analysed by screening using L. pneumophila-specific RealTime PCR (Roche), cultivation of the positive RT-PCRs, serotyping (BioRad)of the live isolates and further genotyping (PFGE).

Results and discussion:  

The RT-PCR screening revealed positive results of L. pneumophila genetic material from 18 of the 39 cabins (46%). Cultivation rendered live L. pneumophila from 22 spots and of these, 21 were L. pneumophila, serotype 1. The epidemiological relations were determined by PFGE analyses showing four different genotypes, of which one was dominant in the environment. Among the other three genotypes, two were found in more than one spot, while one of the genotypes only was found in one spot. The latter was identical to the infection genotype, and was not found in the shower of the cabin belonging to the patient but from the shower in a guest cabin not in ordinary use, but used in connection with sunbathing on deck. In conclusion, use of screening investigations by of specific L. pneumophila-PCR seem to be a good and rapid tool to indicate specific exposure. By further analyses including cultivation, serotyping and genotyping, the true source are possible to identify also in environments which are strongly contaminated with Legionella.