FIELD-STUDY TO OBTAIN LEGIONELLA-FREE WATER FROM SHOWERS AND SINKS OFA TRANSPLANTATION UNIT BY A SYSTEM OF WATER-FILTERS

The efficiency of filters for elimination of Legionella was examined i n a ten month field study. Showers and sinks of twelve patient rooms w ere equipped with nylon 66-polyamid filters. Before filtration the tot al number oi colonies was very high with an arithmetical mean of 1131 cfu/ml. This could be reduced by filtration at the sinks ((x) over bar = 205 cfu/ml). After equipping showers with filters we found a signif icant increase in the total number of colonies ((x) over bar = 1961 cf u/ml). In non-filtered water we found Legionella in nearly 90% of the 648 samples, the concentration extended to 300 cfu/ml ((x) over bar = 51 cfu/ml). After filtration the concentration of Legionella was up to 280 cfu/ml in 7.3% of the 665 samples. We calculated a logistic regre ssion model to examine the effects of the age of the filters and the d uration of their use since the last sterilization. These parameters we re calculated from the time of the break through or retrograde contami nation with Legionella. There were clear differences between shower an d sink filters. Assuming a 5% probability of break through or retrogra de contamination with Legionella, the sink filters should be sterilize d every 3 weeks without regards to the age of the filters. In contrast the shower filters may be used for 3 weeks if they are sterilized wee kly. If weekly sterilization is not feasible they should be used for 2 weeks only. In our study it was not possible to achieve Legionella-fr ee water by changing either the frequency of sterilization or the age of the filters.