Legionella in primary school hot water systems from two municipalities in the Danish capital region

Abstract
EU has specified a maximum Legionella content of 1,000 CFU/L in public hot water systems. School water systems are of particular interest because vulnerable groups use these facilities. Levels of Legionella were investigated in hot water systems from primary schools in two Danish municipalities. Forty-nine schools were evaluated, and 97% and 100% of the schools in Municipality 1 and 2 respectively had Legionella in their hot water systems, even though Legionella-reducing procedures are performed. The content of Legionella colonies was significantly higher in schools in Municipality 1, probably because of lower water temperatures. At stable temperature, 76% of the schools in Municipality 1 and 50% in the other had more than 1,000 CFU/L. When first-flush samples were included, 83% and 87% of the schools respectively had Legionella levels above 1,000 CFU/L. Furthermore, 32% of the schools in Municipality 1 had levels exceeding 10,000 CFU/L up to a maximum of 100,000 CFU/L. Stabile peripheral water temperatures were achieved after 3 min. Tap temperatures above 54 °C and central tank temperatures at 60 °C were associated with Legionella contents below 1,000 CFU/L. Legionella procedures should be evaluated in relation to the above to prevent Legionella levels from exceeding 1,000 CFU/L.