Failure of Legionella pneumophila sensitivities to predict culture results from disinfectant-treated air-conditioning cooling towers

The disinfection of cooling towers based on manufacturers' treatment protocols, as employed in units installed at various public gathering places in Dallas, Tex. (hotels, municipal auditorium), and at the city health department, was evaluated for effectiveness in controlling Legionella pneumophila and compared with previous laboratory studies. In specimens collected in September and December, 1978, L. pneumophila was isolated from 2 of 4 specimens from untreated cooling towers, 2 of 4 specimens from towers treated with agents deemed ineffective in earlier laboratory tests, 6 of 11 specimens from towers treated with putatively effective agents, and 0 of 4 specimens from towers treated with an agent unknown efficacy. These results suggest the need for further studies to identify biocidal agents effective in eliminating L. pneumophila from air-conditioning cooling towers.</jats:p

Laboratory studies of disinfectants against Legionella pneumophila

Legionella pneumophila suspended in tap water was exposed to biocides recommended for inhibiting biological growth in cooling towers and evaporative condensers of air-conditioning systems. Chlorine, 2,2-dibromo-3-nitrilopropionamide, and a compound containing didecyldimethylammonium chloride and isopropanol were effective in destroying concentratiois of 10(5) to 10(6) viable cells per ml. Formulations consisting of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, disodium ethylene bis(thiocarbamate) and sodium dimethyl dithiocarbamate, and a phenolic with pentachlorophenate and sodium salts of other chlorophenols were less effective.</jats:p