Water Journal November - December 1998

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Volume 25 No 6 November/December 1998 Journal Australian Water & Wastewater AssociationEdltorlal Board FR Bishop, Chairman B N Anderson, M R Chapman, P Draayers,…
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Volume 25 No 6 November/December 1998 Journal Australian Water & Wastewater AssociationEdltorlal Board FR Bishop, Chairman B N Anderson, M R Chapman, P Draayers, W J D ulfer, P Gin, GA Holder, M Muntisov, P Nadebaum , J D Parker, M Pascoe, A J Priestley, ] Rissman, F Roddick, EA Swi nton[Jl Water is a refereed journal. This symbol indicates that a paper has been refereed. General Editor Margaret Metz, email: mmetz@awwa.asn .au AWWA Federal Office (see postal address below)Features Editor EA (Bob) Swinton 4 Pleasant View Cres, Wheelers Hill Vic 3150 T el/ Fax (03) 9560 4752 Email: swintonb@c031.aone.net.auBranch CorrespondentsCONTENTS From the Federal President ..... ........ .... .................. ..... ........ .......... ... ...... .... .... 2 From the Executive Director ..... .. ...... .................... .. ......... ..... ..... .... .... ...... ..... . 4ACT - Ian Bergman Tel (02) 6230 1039 Fax (02) 6230 6265MYNew South Wales - Mitchell Laginestra T el (02) 9412 9974 Fax (02) 9412 9676Northern Territory - Mike Lawton T el (08) 8924 6411 Fax (08) 8924 6410Queensland - Tom Belgrave Tel (08) 8227 1111 Fax (08) 8227 1100Tasmania - Ed Kleywegt T el (03) 6238 284 1 Fax (036) 234 7 109Victoria - Mike Muntisov T el (03) 9278 2200 Fax (03) 9600 1300Western Australia- Jane Oliver Tel (08) 9380 7454 Fax (08) 9388 1908Advertising & Administration AWWA Federal Office PO Box 388, Artam,on NSW 1570 Level 2, 44 H ampden Road, Artarmon Tel (02) 9413 1288 Fax (02) 9413 1047 Email: info@awwa.asn.au Advertising: Angela Makris Graphic Design: Elizabeth WanWater (ISSN 0310 路 0367) is published six times per year: Jan uary, M arch, May, July, September, N ovember byAustrallan Water & Wastewater Association Inc ARBN 054 253 066Federal PresidentOFVIEWHave We Failed? .. ....... ...... .... ....... .......................... ... .... ............. ................ ...... 3 F Bishop WATERTel (07) 3810 7967 Fax (07) 3810 7964South Australia - Angela ColliverPOINTTomorrow's Water Scientists ............... .... ... .... ... ........... .... .... .... ....... ... ........... 9 A M akris 路, Early Detection of Outbreaks Of Waterborne Gastroenteritis .... ... ..... 11 A Padiglione, C K Fairley ~ Size Is Important ............. ..... ... .... .. ....................... .. ..... .. .... .... .... ..... .......... 16 G N ewcombe, C Pelekani, C H epplewhite, K N guyen Safe Drinking Water: Are Food Guidelines the Answer? ......... .......... .. 21 D D eere, A Davidson WASTEWATER ~Trialling the CDS Screening System on Raw Sewage ................ .. ......... 26 NW Swain, RA Jago ~ Health Risks of Medlclnal Residues: More Questions than Answers 30 D Wiesner Dewaterlng and Stablllslng Sludge ..... .... ...... .. ............ .... .. .... ... ................... 33 M Laginestra ENVIRONMENT[![ Nutrient Release From Sediments: The Effect Of Short-term Anoxla 35 M GhisalbertiGreg CawstonBUSINESSExecutive Director Chris Davis Au stralian Water & W astewater Association (AWW A) assumes no responsibili ty for opinions or statements of fac ts expressed by contributors or advertisers . Editorials do not necessarily represent official AWW A poli cy. Advertisements are in cluded as an infonnation service to readers and are reviewed before publication to ensure relevan ce to the water environment and obj ectives of AWWA. All material in Water is copyright and should not be reproduced w holly or in part without th e written pennission of the General Editor.Subscriptions Water is sent to all members of AWW A as one of me privileges of membership. Non-members can obtain Water on subscription at an ann ual subscription rate of$50 (surface mail).~Risk Management Strategies for Recoverable Resources ..... ............. 38 S Davis, A Roche WSAAfacts 1997: A Snapshot of the Australian Urban Water Industry .. 42 T Carpenter DEPARTMENTS路路From the Bottom of the Well .. .............. ... ... .... ................. ........ ....... ...... ...... ... 4 International Afflllates ...................................... ...... ...... ....... ...... .... ............... 5 Letter to the Editor ................ .. ... ....... .. .. ..... .. ... ...... ........ .... .... ...... .. ...... ... .. .. .. 10 'Crypto' Crossword ............................... ... ......... .................. .... .. .... .. ........... ... . 10 Meetings .. ............ ........ ....... ..... ... .. ....... ............ ..... .. .. ... ...... .. ..... ... ............. ..... 48 OUR COVER : To enhance product safety the food industry is respo nding to new regulations stipulating the use of quality assurance rather than end product testing. Whilst foodstuffs and drinks, including bottled wa ter, are subj ect to the regulations, drinking water supplies are con sidered very low risk and are exempt. With tighter regulations being called for regarding water supply safety, the food industry experience suggests that a quality assurance approach co uld be the most protective, workable and cost-effec tive response.Photo courtesy of South East WatermWATEREARLY DETECTION OF OUTBREAKS OFWATERBORNE¡ GASTROENTERITIS A Padiglione, C K Fairley'Factors that contributed to the identification of this outbreak included: Widespread Absenteeism (hospital employees, students and school teachers); Increased Emergency Department attendances for diarrhoea; Citywide shortage of antidiarrhoeal medication. (Nonetheless) .. . the waterborne nature of the outbreak was not identified until at least 2 weeks after the onset of the outbreak.' -CDC assessment of the 1993 Milwaukee outbreak (Kramer et al., 1996) A project co nducted by the Coopera tive Research Centre (CRC) for Water Quality and Treatment reviewed the ability of current surveillance mechanisms to rapidly identify a waterborne outbreak of gastroenteritis and concluded the current mechanisms have low sensitivity with considerable lag periods. The project then aimed to identify if m ore rapid techniques were available and evaluated newer computerised data sources such as ho spital emergency department attendances and processing of faecal specimens by pathology laboratories, the latter appearing to be the most sensitive. .Superimposing the estimated impact of an outbreak over the background of endemic gastroenteritis from all sources demonstrated the difficulty involved. Geographical information may reduce the 'noi se' of endemic gastroenteritis since it could highlight particular water distribution zones. Monitoring of pharmaceutical sales is a possibility for the future, but monitoring absenteeism at schools and workplaces presents major logistical problems.Key Words Waterborne disease, gastroenteritis, surveillance, n1.onitoring diseaseIntroduction Drinking water may be associated with very large outbreaks of gastro-enteritis and in rare instances death (Moore et al., 1993; Aho et al. , 1989; Hayes et al., 1989; Richardson et al., 199 1). MacKenzie et al. (1994) reported that in the highly publicised outbreak in Milwaukee more than one million individuals were exposed over a two-week period to drinking water that was contaminated with Ciyptosporidium , resulting in 400 ,000 cases of gastroenteritis. It is interesting that this large outbreak was identified in part because of a dramatic increase in sales of an ti-di arrhoeal medications . Many waterborne outbreaks are detected due to serendipity rather than active surveillance (Frost, 1996). Earlier identification of waterborne o utbreaks of gastroenteritis should allow earlier intervention and investigation to occur. This would minimise the impact of outbreaks and maximise the lessons to be learnt from them. The ability of current surveillance mechanisms to rapidly detect waterborne outbreaks is unknown but is genera lly felt to be low. A 1988 workshop convened by the Environmental Protection Agency in the United States (USEPA, 1990) recommended the use of computerised data as a long-term goal of surveillance programs. However, regular surveillance of hospital emergency department attendances, absentee rates from schools, pharmaceutical sales and faecal specimens processed is not routinedespite the existence 'of some circumstantial evidence that suggests these data sources may be good indicators of wa terborne disease. For example, in an analysis of the wa ter supply in Milwa ukee Morris (1996) noted a close correlation between rates of gastroenteritis in children and water turbidity in the 16 months before the outbreak. This relationship was strongest for children, a finding that ha s been confirmed by Schwartz et al. (1997) in Philadelphia using data over a longer period and also more sophistica ted statistical methods that took into account other factors such as ambient temperature and rainfall. This occurred despite turbidity levels during the study period being within the range stipulated by the statutory autho ri ties. Whether such a relationship would apply in a city with protected water catchments such as Melbourne is not known. In this paper the current surveillance programs that are in place to detect a waterborne outbreak of gastroenteritis are exarnined, as well as their sensitivity and delays in reporting. Various new data sources that could act as markers of gastroenteritis in the community are then examined.Background and Methods Current Gastroenteritis Reporting Retrospective data on cases of WATER NOVEMBER/ DECEMBER 199811WATER gastroenteritis reported to the H ealth Department of Victoria was obtained from computerised records for 1996. This data is collected on the date of onset of symptoms and includes the patient's age and hom e post code, the specific diagno sis if known and the date reported. W e determined the interval between the onset of symptoms and the date the report was received, excluding cases where this interval was recorded as 'O' days, since this was the default code used w hen the date of onset of the di sease was not know n.Faecal Specimens The daily number of specimens processed by the two largest pathology ¡ companies in M elbourne was obtained for the period 1- 1- 95 to 31- 12-96 inclusive. Because specimens are delivered to both laboratories by dedicated co uriers, the vast maj ority arrive on the day of collection . D emographic details and the nature of tests requested are entered into the central database on arrival, before specimen processing. Information on the number of fa ecal sp ecimen s tes ted in Victoria was derived from M edicare records.Hospitals Gastt oenteritis rates in children (<17 years) were obtained from computerised records at the Melbourne Royal Children 's Hospital, Monash M edical Centre and Frankston H ospital. As each patient arrives at the emergency department , their demographic data (nam e, date of birth , sex, address , post code and next of kin) is recorded by administra-tive staff. The . system at the Royal Children 's Hospital (' HAS Sys tem s Australia') then informs the m edical staff that the patient is waiting. After consultation the likely diagno sis is entered into the system by the medical staff. The computer codes the diagnosis u sing a standardise d international coding sys tem, the ' International Classification of Di seases : Version 9' (ICD-9) . The ICD-9 codes that were used to code acute gastroenteritis at this hospital in the study period w ere 9 .1 , 9.2 and 558.9 . This patient managem ent sys tem has now been implemented in most of the public hospital em ergency departments in Au stralia. A similar but more rudimentary system is in operation at Frankston Hospital.Results Current Gastroenteritis Reporting Only 71 cases of 'presumed food and waterborne illness' were received by the H ealth D epartment ofVictoria in 1996 (Infectious Diseases Unit , 1996). M any cases initially rep orted under thi s category are reclassified once the cause is known. Thi s data (encompassing cases due to a range of organisms such as Blastocystis, Cryptosporidium, E. coli etc.) was not further analysed due to the small numbers. The vast majority of gastroenteritis reports derive fro m laboratory staff w hen they isolate specific organism s. The m edian interval between onset of disease and reporting to the H ealth D epartment fo r cases of Campylobacter and Giardia was 13.8 and 15 .8 days respectively. Even if one excludes thelate reports (those >1 month), the median interval was still greater than ten days for both. These figures are felt by H ealth D epartment officials to be significant underestimates. The date of onset of disease is often not known , and an alternative date such as the date of collec tion of the specimen is u sed instead. In order to estimate the number of reports which might flo w from an outbreak of, say, 20 ,000 , 50,000 or 100 ,000 cases .of gastroenteritis, a numb er of factors w hich interven e between the actual number of cases and the numb er of reports have to be applied. These factors are based mainly on previous experience (see T able 1). Figure 1 reveals the reported incidence of giardiasis for M elbourne during 1996 and shows the expected impacts that large outbreaks of w aterborne giardiasis would have on these background rates. To illu strate how difficult it w ould be to detect such outbreaks, we sup erimpo sed these peaks over the n atural 'n01 se' (see Figure 2).New Data Sources It is important to no te that the vast maj ority of people with gastroenteritis do not attend a doctor but either stay home or go to a pharmacy to buy something over the counter. Each data source was evaluated as to its utility. However, monitoring of pharmaceutical sales and absenteeism in schools or workplaces would not appear to be simple with current technology. Similarly, real time monitoring of visits to general practitioners would proveTable 1 Assumptions used in modelling of outbreaks of gastroenteritis AssumptionEvidence from previous waterborne outbreaks50% of faeca l specimens from people with Giardia are identified as suchsee Mandell et al., 1995, p. 24900.65% of community gastroenteritis have faeca l specimens taken8.3% of gastroenteritis cases attend GP (Garthright et al., 1988) No. of GP visits for gastroenteritis Vic/year= 300,000 (Hellard and Fairley, 1997) No. of patients who had faecal specimens examined for parasites Vic/year = 24,500 (Medicare data provided by Health Insurance Commission, Canberra)= 0.678%85% of community faecal specimens are surveyedDerived from data supplied by pathology compan ies, Health Insurance Commission (data not shown for commercial reasons)1% of cases attend emergency department (worst case scenario 0.6%)Cryptosporidium: 83% attend GP, 5% 'hospitalised': we ll documented outbreak in UK (Outbreak Control Team, 1996); >1% 'hospita lised' in large Mi lwaukee outbreak (Morris et al., 1996) Salmonella: 2.3% 'hospita lised' in US outbreak (Angu lo et al., 1997)40% of cases are in chi ldren (worst case scenario 35%; best 45%)43% of cases in children <15 years old in well documented waterborne cryptosporidiosis outbreak in UK (Outbreak Control Team, 1996)65% of paediatric hospita l attendances attend the monitored hospitals (worst case scenario 60%; best 75%)65% actua lly attended in 1996Norma lly distributed over 3 weeks (SD=3 days) 65% of paediatric gastroenteritis cases are coded as such (worst case scenario 60%; best 75%)Other wel l described cryptosporidiosis outbreaks in the US and UK fit this criterion (Outbreak Control Team, 1996; MacKenzie et al., 1994; Leland et al., 1993) No published data: Emergency department director's consensus that th is is a reasonable and conservative figure12WATER NOVEMBER/DECEMBER 1998'WATER 30Modelled outbreaks 100,0002550,000 2020,000i815102/2196513/966141968151969l6f9e11n/9e12/819e1319195 15110/"96 16f l1 /'9G 181 12/9e HW1/9720/2/97241319 72514197271519728161'11730/719731 /Ml7DateFigure 1 Giardiasis in Melbourne, with modelling of anticipated reports from outbreaks 30Hospitals Gastroenteritis rates in children (<1 7 years) at the major em ergency departments in M elbourne over a 20-month period are presented in Figure 4. W e obtained data from the Royal Children's, W estern (Sunshine campus) and Franks ton Hospitals. T hese three hospitals see 65% of such patients in M elbourne (data not shown). M onash M edical Centre was not included in the analysis since it has been computerised only since the latter half of 1996. Again, we m odelled the expec ted impact of o utbreaks of gastroenteritis m M elbourne of 20, 000 , 50 ,000 and 100 ,000 cases, ass uming a stable background rate of endemic gastroenteritis. It is important to note that the accuracy of the modelling is highly dependent on the assumptions used. Figure 5 shows the outcome w hen a 'worst case' set of assumptions is used . Likewise, Figure 6 shows the outcome w ith m o re ge nerou s ass umptions. These are n o t unrealistic: 75% of hospitals could now be easily monitored by adding in the data from the M o nas h M edical Centre, the o ther m aj or paediatric hospital in M elbourne.Modelled outbreaks : 100,000"5,000,.20,000l! ".8E :,z10DateFigure 2 Giard iasis in Melbourne (modell ing superimposed on natural variation) 140,:, 120 Cl>file,ooSalmonella outbreak in peanut butter reported in media June 20Modelled outbreaks 100,000.,Q.50,000C~8020,000·u8..,M elbourne . Figure 3 reveals the number of faecal specimens handled on a daily basis throughout 1996. Noteworthy is the large increase in specimens processed in late June, w hich coincides with the release of publicity conce rning a fo od poisoning scare of Salm on ella m peanut butter. (Interestingly, laborato ry staff did not notice an increase in the total number of Salmonella isolated at this time-the outbreak was identified because of the unu sual type of Salmon ella isolated rather than an increas~ in the overall numbers. W e then modelled the expected impac t of outbreaks of gastroenteritis in M elbourne of 20,000 , 50,000 and 100 ,000 cases, assuming a stable background rate of endemic gastroenteritis (see Figure 3) .00~.u.. ••,. +--+--+---<--t-+-+-+---+--+--+--+--+-'--+-+-+-+-+--+---<--t-+-+-+---+---+--+--+--+--+-+-+-+-"'a,"'a, "'a,<O<O<OC'%'.% l, <O~ <O~ u.. u. :::, :::,q,-"l -"l., .,<Oa,~C.<Oa, ~C.< <<O<Oa,a,<O<O>, >,:::, :::,"'a, '% "''%<O<O-al -al -al ~<O-,Cq, ~ :,"'%% :ll6. "'a,6. a, "'a, ., 013 013 :, :, ., <O< <<O(/)(/)"' ~ ~ 'I;., z0 z0 0 0~ <O<O<Oa,"'a, ....q, ....'% ....l,a, ....'.% ....a, ....a, ., ., ., "' :::,"' 0" -"l -"l u. u. :::, C~~DateFigure 3 Faecal specimens processed in Melbourne, with modelling of outbreaks of gastroenteriti sexorbitantly expensive . Two data sources appeared to show the most po tential: emergency department attendance figures and processing of faecal specimen s by pathology laboratories . Each of these shares the attributes of being: • already collec ted on elec tronic databases in real time • a short interval between disease onset and data collection • potentially accessible at low cost.Accordingly, we obtained data from these two sources and then modelled the expec ted effec t on these data so urces of w aterb orne o utbrea ks of 20,000, 50,000 and 100,000 cases, assuming a stable background rate of endemic gastroenteritis and using the assumptions presented in T able 1.Faecal Specimens The two largest private laboratories handle around 85 % of the faecal specimens tested by general practitioners inDiscussion M any wa terb orne o utbreaks are detected due to serendipity rather than active surveillance. Earlier identification of wa terborne ou tbreak s of gastroenteriti s should allow e
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