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time periods (Be ntham and Broadbent 1993). Most recently a statistical analysis of sampling frequen cy from Legio11ellac o l o n is e d coo lin g towers ha s demonstrated that monthly samples are not representative. In most cases the result will not bear any statistica l relation to the c urrent sta tus of the Legio11ella popu lation once it is available after the usual 7- l 0 days cu.lture period (Bentham 2000). These reports ha ve shown that a mo nthly frequency of sa mpling will not provide a representative picture of Legio11ella colonisation and so ca lJ into question the validity of the action directives. It has been argu ed that mo nthly sa mpli ng is va lid in that it will eventually detec t the presence of the o rga nism in cooli ng water, and so ale rt the ope rator to the need fo r vigilan ce in their maintenance program. H owever, field stu dies have demonstrated colon isation of greater than 65% of cooling towers in any one yea r, and in one instance 99% (83/84) of systems over a four year period (Koide et al 1993, Bentham el al 1992) . It has also been repo rted that on ce a cooling syste m has been colon ised Lel/icmella cannot be eradica ted (Flie rmans 1996). If these data can be relied upo n, then they suggest that the use of cu lture in detecting the presence of Legio11ella in a coo ling syste m is fo r the m ost part superfluous. T he need for vigilance exists aside from c u lture results, as it is most likely that Legio11ella coul d be isolated at some poi nt from almost any cooling towe r in service . T he emphasis should be based upon control of the organism s rather than erad icati on . Published evid ence suggests that th is ca n be achieved through appropriate design and ma intenan ce (Fliermans 1996) .

Aerosol Dissemination Legio11ella infection is initi ated by inhala tion into the lungs of the bacteria carried in fine water droplets (aerosol) released from the coo ling tower. It should be noted that concentratio ns of bacteria in the bulk water of a syste m ca nnot be re lated to co n centrations leaving the system in aerosol. Properly designed and fitted drift eli minato rs in cooling systems ca n dramatically reduce the release of aerosol, but it can never be totally prevented (AS/NZS3666: 1995). Enviro nmental variables such as relative humidity, dilution, cloud cover, UV radiation intensity, and wind velocity will all affect the survival and dispersa l of aerosol (Addiss et al 1989, Fliermans 1996). These fac to rs may be a partial explanation of the ten de ncy for disease o utbreaks in the autumn period when climatic conditions better support aerosol

dissemination (Ben tham and Broadbent methods used for culture from cooli ng 1993). The longer a wa ter droplet is water are aggressive and may result in a carried in the air the smaller it becomes significa nt loss in sensitivity (Ta el al 1995, due to evaporatio n , concentratin g its Fliermans 1996) . Legio11ella are co nsidered contents. Droplets may leave the cooling to be fastidious organisms on laboratory syste m at sizes too large to be inhaled and media, and may be out-competed by other e vaporate down to resp irable particl es organisms on the agar plate (Flierma ns wi th their co nten ts concentrated ma ny 1996) . This fastidiousness is most likely times ove r. Du e to the range and related to the ecology of Le~eiimella. These variation of th e facto rs influe ncing this bacteria arc oppo rtu nists rel iant on other phenomenon the concentratio n factor is microbia l species to fulfil their nutritional incalculable. T o compli cate this further requirements. there is no established infective dose fo r A number of o rganisms have been Legio11e/la. It is presum ed that infecti vity isolated that appear to be obligate intrais largely a func tion of the immune status cellular pathogens of amoebae, and cannot of the host combined w ith the exposure be isolated from primary cultures on tim e an d conce ntrations of the organism selective media (Adeleke et al 1996) . Viable (Fliermans 1996). Legio11ella p11e11mophi/a capable of causing Ecological fac to rs with in the cooling infection have also been reported to be not water syste m w ill also influ en ce the detectable by conventional cul ture fro m dissemination, stab ility and viability o f water samples (Atlas 1999) . The growth Legionella within aerosol. Cyanobacterial of Legio11clla in pure cul ture is an artific ial and algal species are commonly present environmen t fo r the organ ism and in coo ling wate r systems that may therefore li kely t o be i nse n sit ive. enhance the time pe1iod that Legio11ella can Laboratory comparisons between convensurvive in aerosol (Berendt 1981). tional culture and PCR techniques have also demonstrated th is lack in sensitiv ity l t has been shown that Legio11ella may (A tlas 1999). also be carried in amoebic vesicles of respirable size (Berk el al 1998). These T here is a well-established inter- and vesicles may contain many hundreds of intra- species variation in virulence of bacteria, and inhalation of one such vesicle may be su ffi cient to cause disease. It has been postulated that culture of water samples The Urban Water Review 1999/2000 is now avai lable. containing these Providing an overview of the performance of Victoria's ves icles woul d 1 8 urban wa ter utilities, the review reports on : result in a single • financial colony arising on the cu ltur e • service m e dium. T hi s • operational wou ld grossly indicators for wate r and wastewater services. unde restimate the The report covers 5 years of data, provid ing anql~sis of true concentration trends by of organisms in the sam ple (Be rk • Melbourne metropolitan et al 1998). • non metro polita n urba n > 35000 properties

The Victorian Urban Water Industry in review

Culture Results Th e i ss u es surrounding culture for Legio11ella are also contentiou s. C ultur e techniques for L egio11ella a r e variable, and to some extent species specific (T a et al 1995). The pretreatment

• non metropol itan urban < 35000 properti es as well as state wide and individual fig ures. A vital reference book fo r all of those in volved in the industry.

Available from:

Victorian Water Industry Association Suite l, Level 6, 2 Collins Street Melbourne 30000 Ph: (03) 9639 8868 fax: (OJ) 9639 8860 Email: Price: $77.00 {including GST, postage and packaging within Aust.) WATER MARCH 2001


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Water Journal March 2001  

Water Journal March 2001