Jorrrnal of IIospital Infection (1988) 12, 280-294

Monitoring the bacteriological quality of potable waters in hospital

P. R. Hunter & Susan H. Burge

Public Health Laboratory, University Hospital of Wales, (2274 4xw

Heath Park, Cardi

AcceptedJFor publication 4 May 1988

Summary: We report a survey of the bacteriological quality of potable waters from hospitals. In the 12-month period February 1986 to Tanuarv 1987, 646 samples were examined from 25&hospitals. Colifbrms were-isolate2 from eight (1.2%) samples, received from three hospitals. These hospitals did not, therefore, satisfy the European Community (EC) directive on potable water quality. Three hundred and four (47%) samples had total viable counts higher than the guidelines given in the EC directive on potable waters. Thirteen (52%) of hospitals surveyed submitted at least one unsatisfactory sample and six (24%) submitted more than 50% unsatisfactory samples. Water quality was generally poorer in the summer and autumn. Estimation of the total viable count is an inexpensive and simple method for monitoring the microbial quality of hospital waters.

Keywords: Potable water quality; hospital water quality; water quality assessment.

Introduction

Hospital potable water supplies have been associated with nosocomial infections. Legionella pneumophila infections are the most frequently reported outbreaks associated with hospital water supplies (Fisher-Hoch et al., 1981; Stout et al., 1982; Helms et al., 1983), though Aeromonas hydlophila infections have also been associated (Picard & Goullet, 1987). It is not surprising, therefore, that microbiologists are receiving requests to monitor the microbial quality of water supplies in their hospitals. However, the routine culture of Legionella spp. from water has been discouraged (Bartlett, Macrae & Macfarlane, 1986; Department of Health and Social Security, 1987). Picard & Goullet (1987) did suggest that routine culture for Aeromonas spp. from hospital water was worthwhile. The question remains as to whether routine microbiological surveillance of hospital potable water, by standard methods (Department of Health and Social Security, 1983), is of value in detecting high-risk water supplies. No information about the

Correpondence to: Dr. P. R. Hunter, Division of Hospital Infection, Central Public Health laboratory, 61 Colindale Avenue, London NW9 5HT.

01954701/88/080289+06 $03.00/O

289 0 1988 The Hospital Infection Society

290 P.R. Hunter and S. H. Burge

general quality of potable waters in hospitals is available for the UK. We report our experiences of examining hospital potable waters over a 12-month period.

Materials and methods

The bacteriological results of hospital potable waters, received during the 12-month period, from February 1986 to January 1987, were analysed. These waters had been submitted to the laboratory by Environmental Health Officers (EHOs) and hospital engineers as part of their routine assessment of water quality. Non-potable waters, such as those from hot taps, bathroom and toilet areas, and header tanks were excluded from the study.

Water sampling procedures differ slightly between local authorities in South Wales, though samples are usually taken after flaming the end of the tap with a blow torch (except for plastic fittings) and running water to waste. 300 ml samples are then taken into sterile bottles and the water samples transferred to the laboratory within a cool box. All waters included in the study were examined within 6 h of sampling. The majority of samples were obtained from ‘rising mains’, but EHOs and hospital engineers were often uncertain of the supply for each sampled tap.

Coliform counts were performed by the membrane filtration of 100 ml water samples and culture of the membranes on Membrane Enriched Teepol Broth (DHSS, 1983). The identity of presumptive coliform colonies was confirmed by subculture into lactose peptone water for acid and gas production. Coliforms gave yellow colonies on membrane culture and acid and gas in lactose peptone water. Escherichia coli were identified by subculture of all coliform colonies into Lauryl Tryptose Mannitol Broth with tryptophan, incubated at 44”C, E. coli producing acid and giving a positive indole reaction after the addition of Kovac’s reagent. Total viable counts were performed by culture of two 1 ml samples in 15 ml pour plates of plate count agar OM325 (Oxoid, Basingstoke, England). One was then incubated at 37°C for 24 h and the other at 22°C for 72 h (D.H.S.S., 1983). All media, except where stated, were produced in the laboratory according to published recipes (DHSS, 1983).

Results

Six hundred and forty-six samples were submitted from 25 hospitals including most of the major hospitals within the catchment area of the laboratory. The number of samples examined per hospital ranged from 1 to 140 (mean 25.8; median 6). There was a marked variation in the number of samples received each month. 32% of the waters were examined in July, 12% in September, 11% in October, 8% in April, 7% in January and August, 6% in June and November, 4% in May and December and 2% in

Quality of hospital waters 291

February and March. The majority of samples had been taken from central or ward kitchens.

Coliforms were isolated from eight (1.2%) samples, received from three hospitals. These ranged from 1 to 37 (median 3) organisms per 100 ml, three were repeat samples from the same fitting. Escherichia coli was isolated from three (0.5%) samples, received from two hospitals. There were two counts of one and one of 30 per 100 ml. Six of the eight samples with positive coliform counts also had unsatisfactory total viable counts. Those with satisfactory total counts had the lowest coliform counts (1 and 2 coliforms per 100 ml).

The total viable counts of all 646 samples are shown in Table 1. Of these samples 304 (47’/ ) o were unsatisfactory, according to the guidelines on total viable counts contained in the European Community directive on potable water (European Community, 1980), at either or both incubation temperatures. Eighty-four (13 O/o) samples had total viable counts at least 10 times higher than the guideline limits. Of the 2.5 hospitals surveyed 13 (52%) submitted at least one unsatisfactory sample and six (24%) submitted unsatisfactory samples on 50% or more occasions. Seven hospitals submitted greater than 30 samples during the study. These seven hospitals submitted 523 samples of which 288 (55’1) 0 were unsatisfactory, compared to 16 of 123 (13 “A) samples for the remaining hospitals. There was a striking seasonal variation in the proportion of samples received which were unsatisfactory (Figure 1).

Table I. Total viable counts of potable waters from hospitals

Temperature of Colonies per ml incubation

Cl0 11-100 101-1000 > 1000

22°C 285 148 163 50 37°C 464 134 37 11

It was not possible to analyse separately waters taken direct from a rising main and those which had been stored in header tanks. However, in five hospitals with particularly poor records, three only submitted samples taken directly from rising mains and two submitted both direct and indirect samples. Those hospitals subrnitting entirely direct samples had high total counts in 3 1%) 48% and 63 % of samples compared to 5 5 % and 58 % for the other two hospitals. This would suggest that water from a rising main is not necessarily of higher quality than that from a header tank. Water flow through header tanks in hospitals can be particularly rapid. Whether water quality from header tanks deteriorates at night and week-ends, when demand is low and flow through the system drops, is not known.

P. R. Hunter and S. H. Burge

Figure 1. The proportion of hospital potable waters which were unsatisfactory in each study month. Cl, Total viable count (TVC) over European Community (EC) guidelines; n , TVC 10 times over EC guidelines.

Discussion

The relevance of coliform counts to water safety has always been controversial and the relevance of total viable counts is even more so. Nevertheless, the European Community (1980) directive on potable water has set maximum acceptable coliform counts (< 1 in 100 ml) and given guidelines on maximum satisfactory total viable counts (10 ml-’ at 37°C and 100 ml-’ at 22°C). In any year 95% of samples are expected to fall within the guidelines. This directive applies to all water intended for human consumption including that in hospitals (Lewis, 1983). The consumption of water with high total counts is not forbidden by the directive, though it does suggest that the supply should be investigated if total counts are repeatedly high. A further legal requirement for a wholesome water supply is contained in the food hygiene regulations (Ministry of Agriculture, Fisheries and Food, 1970).

It is reassuring that so few waters yielded coliforms. However, it is a cause of some concern that so many had high total viable counts. To some extent these results are artificially high, since those hospitals with a previous unsatisfactory result submitted repeat samples. Nevertheless, a half of all hospitals submitting specimens had at least one unsatisfactory sample and a quarter more than 50% unsatisfactory samples. Whether or not those hospitals whose water supplies yield high total counts can be assumed to

Quality of hospital waters 293

satisfy the requirements of the food hygiene regulations (M.A.F.F., 1970) for a wholesome water supply remains to be seen.

High total counts in potable water samples indicate deterioration in the distribution system (Ptak 2%~ Ginsberg, 1977). This probably results in stagnation of the supply, allowing warming of the water and, in turn, bacterial multiplication. This suggestion is supported by the increase in total counts seen during the warmer summer and autumn months. Indeed, some of the hospitals, which submitted unsatisfactory samples, had problems of this nature due to overlong rising mains or storage in header-tanks.

Total viable count estimations have not been used as an indication of a water supply’s safety as, until recently, most investigators were only interested in indicators of fa’ecal contamination (Kott, 1977). There is no suggestion that water with high total counts is a health hazard in itself. However, it has been shown that the presence of a diverse bacterial flora supports the growth of Legionella pneumophila in potable waters (Wadowsky & Yee, 1985). That high total counts may be associated with the growth of Aeromonas spp., is suggested by the same seasonal variation (Burke, 1984; Picard & Goullet, 1987). We would suggest that continually high or a sudden unexplained increase in total viable counts in hospital water may indicate an increased risk from legionellas or aeromonads. This would also apply to non-potable, hot water systems and is recommended in the second report of the committee of inquiry into the outbreak of Legionnaires’ disease in Stafford in April 1985 (DHSS, 1987). Further study of the relationship between total viable counts and the isolation of these pathogens is clearly warranted.

We do not believe that routine examination of hospital potable waters for either Legionella spp. or Aeromonas spp. is worthwhile. Their culture and identification is expensive and time consuming. The question remains as to when hospital water supplies should be examined if at all. If sampling has been requested by an environ.mental health officer as part of his inspection of food handling premises, we would suggest that both coliform and total viable counts be performed, preferably by a laboratory which regularly examines water samples. For general water quality assurance testing, a total viable plate count, which should be within the skill of any clinical bacteriology laboratory, is probably sufficient. Only if total counts are repeatedly unsatisfactory should further examination of the system be undertaken.

We wish to thank Dr C. H. L. Howells for his support.

References

Bartlett, C. L. R, Macrae, A. D. & Macfarlane, J. T. (1986). Surveillance, control and prevention. In Legionella Infections, pp. 12s-149. Edward Arnold, London.

294 P. R. Hunter and S. H. Burge

Burke, V., Robinson, J., Gracey, M., Peterson, D. & Partridge, K. (1984). Isolation of Aeromonas hydrophila from a metropolitan water supply: seasonal correlation with clinical isolates. Applied and Environmental Microbiology 48, 361-366.

Department of Health and Social Security (1983). The bacteriological examination of drinking water supplies 1982. Report on Public Health and Medical Subjects, no. 71. Her Majesty’s Stationery Office, London.

Department of Health and Social Security (1987). Second report of the committee of inquiry into the outbreak of Legionnaires’ disease in Stafford in April 1985. Her Majesty’s Stationery Office, London.

European Community (1980). Council Directive No. 80/778/EEC of 15 July 1980 relating to the quality of water intended for human consumption. Oficial Journal of the European Communities L229, 1 l-28.

Fisher-Hoch, S. P., Bartlett, C. L. R., Tobin, J. O’H., Gillbert, M. B., Nelson, A. M., Pritchard, J. E., Smith, M. G., Swann, R. A., Talbot, J. M. & Thomas, J. A. (1981). Investigation and control of an outbreak of Legionnaires’ disease in a district general hospital. Lancet i, 932-936.

Helms, C. M., Massanari, R. M., Zeitler, R., Streed, S., Gilchrist, M. J. R., Hall, N., Hausler, W. J., Sywassink, J., Johnson, W., Wintermeyer, L. & Hierholzer, W. J. (1983). Legionnaires’ disease associated with a hospital water system: a cluster of 24 nosocomial cases. Annals of Internal Medicine 99, 172-178.

Kott. Y. (1977). Current concents of indicator bacteria. In Bacterial Indicators/Health kaza;ds Associated with Witer (Hoadley, A. W. & Dutka, B. J., Eds) pp’. 3314. American Society for Testing and Materials, Philadelphia.

Lewis, M. J. (1983). The bacteriological examination of drinking water. Journal of Hygiene 90,143-147.

Ministry of Agriculture, Fisheries and Food (1970). The food hygiene (general) regulations 1970. Statutory Instruments 1970 No. 1172. Her Majesty’s Stationery Office, London.

Picard, 8. & Goullet, Ph. (1987). Seasonal prevalence of nosocomial Aeromonas hydrophila infection related to aeromonas in hospital water. Journal of Hospital Infection 10, 152-155.

Ptak, D. J. & Ginsberg, W. (1977). Bacterial indicators of drinking water quality. In Bacterial Indicators/Health Hazards Associated with Water (Hoadlev, A. W. & Dutka, B. J., Eds), pp. 218-221. American Society for Testing and Materials; Philadelphia.

Stout, J., Yu, V. L., Vickers, R. M. & Shonnard, J. (1982). Potable water supply as the hosital reservoir of Pittsburgh pneumonia agent. Lancet i, 471472.

Wadowsky, R. M. & Yee, R. B. (1985). Effect of Non-Legionellaceae bacteria on the multiplication of Legionella pneumophila in potable water. Applied and Environmental Microbiology 49, 1206-1210.