Comparison of Anolyte and Chlorine Dioxide for a Continuous Hot Water Disinfection in Nursing Home: A Two Years Legionnaires’ Disease Prevention

Worldwide epidemiological reports assert that drinking water is a source for infections and Legionella control represents a critical issue in healthcare settings. Chemical disinfections of water networks are control measures that need to be fine-tuned to obtain satisfactory results in large buildings over prolonged time periods. Aim of study is the evaluation of the effect of anolyte and chlorine dioxide, applied in two different hot water networks of a nursing home to manage Legionella risk. Nursing home has two buildings (A and B), with the same point of aqueduct water entrance. From June 2016, following a shock chlorination, the continuous disinfections with chlorine dioxide and anolyte were applied in hot networks of building A and B, respectively. Hot water was sampled at the central heating system and at two points of use for Legionella research, while chemical tests of manganese (Mn), iron (Fe), zinc (Zn) and trihalomethanes compounds (THM) were implemented to evaluate the disinfection by-products presence. Before chlorination Legionella pneumophila sg1 was recovered with a mean count of 2.4 × 10 CFU/L, while chemical compounds concentrations were within the law limits (Directive 98/83/EC). Then the disinfections Legionella was not recovered in both hot water plants. After the disinfection with chlorine dioxide (from June 2016 to May 2018), a statistically significant increase of iron, zinc and THM concentrations was detected in building A (p = 0.012; p = 0.004; p = 0.008). Both disinfectants appear effective against Legionella spp. growth in water network, but anolyte ensures a lower disinfection by-products release. How to cite this paper: Totaro, M., De Vita, E., Giorgi, S., Profeti, S., Porretta, A., Gallo, A., Frendo, L., Casini, B., Valentini, P., Privitera, G. and Baggiani, A. (2019) Comparison of Anolyte and Chlorine Dioxide for a Continuous Hot Water Disinfection in Nursing Home: A Two Years Legionnaires’ Disease Prevention. Journal of Water Resource and Protection, 11, 233-243. https://doi.org/10.4236/jwarp.2019.113014 Received: January 18, 2019 Accepted: March 3, 2019 Published: March 6, 2019 Copyright © 2019 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access DOI: 10.4236/jwarp.2019.113014 Mar. 6, 2019 233 Journal of Water Resource and Protection


Introduction
Legionella spp. is a waterborne pathogen frequently associated with nosocomial infections, particularly among immunosuppressed, transplanted patients and people undergoing aggressive chemotherapy [1]. Over the last years in Europe, some of the outbreaks of Legionnaires' disease reported by the European surveillance scheme have been linked to hospitals and healthcare facilities having a hot water system colonized by Legionella spp. [2]. Moreover, international and Italian guidelines for Legionnaires' disease prevention [3] [4] suggest that ancient water networks of healthcare facilities provide optimal conditions for Legionella colonization into corroded pipelines and dead leg branches.
Hot water network treatments may be applied with different compounds such as chlorine dioxide [5], sodium hypochlorite [6], monochloramine [7] [8] and hydrogen peroxide [9] ensuring a continuous disinfection procedure. All these treatments are useful to control Legionella spp. counts, but some disinfectants may get worse the chemical water quality after the pipelines corrosion [10]. In fact, worldwide studies reported that high concentrations of toxic disinfection by-products (DBPs) in drinking water favor the probability to be taken up through inhalation, ingestion and dermal absorption, increasing the potential health risks of exposure for the users [11] [12]. For this reason, a planned choice of appropriate pipelines materials and chemical disinfection methods must be done for each healthcare water network [13].
Water disinfection may be achieved by new strategies, such as the electrochemically activated solution generators, which produce two solutions during electrochemically activation of dilute salt solutions: an oxidant solution capable of penetrating biofilm termed anolyte and a catholyte with detergent properties.
In detail, the dilute saline solution is activated by passing through a cylindrical electrolytic cell in which the anodic and cathodic chambers are separated by a permeable membrane. Two separate streams of activated water are produced: anolyte (hypochlorous acid) with a pH range of 2 -6 and an oxidation-reduction potential of +400 mV to +1000 mV. It is an oxidizing compound having an antimicrobial effect. Catholyte (sodium hydroxide, pH of 12 and an oxidation-reduction potential of −900 mV) has surfactant properties and is an antioxidant [14]. Several studies assert the efficacy of anolyte disinfection method in water [15], food [16] [17] and surface samples [18].
In Italian healthcare facilities, despite the increase of critical points linked to water disinfections, electrochemical methods are not frequently applied for hot water treatment. In fact, few published papers about water network disinfection have focused on the comparison between electrochemical and common chemical disinfection.
In this study, we report a plan for Legionnaires' disease prevention, which was scheduled to compare two different water disinfection strategies, applied in an Italian nursing home by using anolyte and chlorine dioxide, for continuous hot water disinfection. Considering the increase of Italian Legionnaires' disease cases linked to hospitals and healthcare facilities, this research may assess the choice of new strategies aimed to improve the chemical disinfection activity in hot water networks.

Nursing Home Setting and Hot Water Disinfections
The healthcare setting is a nursing home of North-Western Tuscany (Italy), organized in two identical buildings (A and B) active since 1975. For both buildings, the architectural structure is a monoblock with a central plate on 3 levels, with 13 rooms and 39 beds. Nursing home hosts non-self-sufficient elderly patients with cognitive and behavioral disorders and chronic degenerative diseases, such as Parkinson-Alzheimer's diseases, cardiovascular diseases, diabetes, etc.
In June 2016, within the Water Safety Plan (WSP) implementation program, the hot water system disinfection, and a systematic monitoring program with samplings at the final points of use, began.
Following the WSP introduction, the municipal drinking water was pre-filtered and softened before entering the two nursing home hot water distribution systems. Despite the old and galvanized steel-made pipelines, hot water networks were treated with in continuous chlorination.
Following a shock chlorination (50 mg/L sodium hypochlorite; 1 h), a continuous disinfection with chlorine dioxide was applied in building A, while anolyte compound was introduced in building B.

Microbiological Hot Water Samplings and Legionella Spp. Research
Before and after the WSP introduction, each building's hot water distribution system was sampled at the recirculation point (R) and at the boiler (B) of the central heating system and at two points of use located at the first and second floors (P1; P2) for Legionella detection, as suggested by Italian Legionnaires' guidelines [3]. Microbiological hot water samplings were performed on a monthly basis. From January 2017 samplings were done on a quarterly basis.
Legionella research and physical-chemical parameters assessment (total chlorine concentration, pH and water temperature) were recorded during the sampling activity.
The isolation of Legionella spp. in hot water samples was performed as suggested by the international standards procedure ISO11731 [19]. Briefly, one liter

Statistical Analysis
The Kolmogorov-Smirnov test was performed to verify the normality of distri-

Legionella Spp. Results
Before WSP implementation, between April 2016 and May 2016, high Legionella pneumophila sg1 concentrations were detected in all the tested water points of use. As shown in Figure 1, Legionella concentrations observed in hot water samples ranged from 1 × 10 4 to 3.5 × 10 4 CFU/L, with a mean value of 2.4 × 10 4 ± 7.1 × 10 3 CFU/L. Moreover, low temperature values were detected in all sampling points (mean value of 38.8˚C ± 4.2˚C).
Considering the absence of hot water disinfection, this data highlight a significant Legionella spp. colonization of both nursing home buildings water distribution systems.
After WSP plan introduction and the application of the two continuous disinfection methods, from June 2016 to June 2018 Legionella spp. was not recovered in both hot water networks.  Table 2 shows physical-chemical results detected from the hot water network

Discussion
According to literature, the application of a plan for Legionella prevention and control is needed in healthcare facilities, mostly in hospitals hosting immunosuppressed patients [24]. Considering some occurrences of Legionnaires' disease outbreaks in nursing homes [25] [26] [27], the implementation of the Water Safety Plan may also be extended to these kinds of healthcare settings.
For this reason, Italian guidelines for Legionnaires' disease prevention and control [3] recommend the application of control measures ensuring a good microbiological quality in water networks. In fact, the choice of an adequate and continuous chemical disinfection system may prevent the occurrence of waterborne pathogens colonization in water pipelines, mostly in high and ancient buildings with large and complex water network having critical points [28] [29].
Despite literature data assert that chlorine dioxide enhances the corrosion process of metal ions, which may be released in drinking water, this is the most common chemical compound disinfectant used for hot water disinfection. In fact, treatment with chlorine dioxide is effective against bacteria, virus and protozoa. If not controlled carefully, chlorine dioxide can corrode pipelines releasing metal ions and disinfection by-products in drinking water, getting worse the organoleptic properties of water [30].
Moreover, alternative techniques using electrochemically-activated solutions are less used, and only few studies support this method for the prevention of microbiological water risk.
Anolyte, applied for drinking water disinfection, can act directly on the biofilm inside the plumbing, eliminating it in few days. It is highly effective in disinfection processes against bacteria (including spores), virus and protozoa. Treatment has low operating costs and the neutral pH is fully compatible with the materials of water networks. Moreover, anolyte does not cause excessive corrosion of pipework [31].
Our comparative study shows how chlorine dioxide and anolyte are able to avoid Legionella spp. growth in both water networks in a long-term period. Although in two years study we always observed a good chemical quality of drinking waters, some statistically significant differences were detected between building A and B. In details, from hot water network treated with chlorine dioxide we observed an increase of metal ions (iron and zinc) and THM concentra-tions in the period between June 2016 and May 2018. This trend was not detected in hot water samplings collected from building B and disinfected with anolyte. However, during the whole period of study chemical results of water sampling collected from the point of aqueduct entrance remained unchanged.
Despite this comparison may confirm the advantage and disadvantage declared in literature, the choice of an appropriate disinfection method for hot drinking water may be continuously controlled as described by the Water Safety Plan [28] [30] [31].

Conclusion
In conclusion, our study is one of the few assessing a technical comparison of two different incontinuous disinfections, which were applied in two separate, similar and pre-contaminated hot water networks. After two years, it is possible to assert that both disinfectants appear effective against Legionella pneumophila sg1 growth in water pipelines, but anolyte ensures a lower metal ions and disinfection by-products (THM) release.