Water-borne bacteria, found in cold water storage tanks, are causative agents for various human infections and diseases including Legionnaires’ disease. Consequently, regular microbiological monitoring of tank water is undertaken as part of the regulatory framework used to control pathogenic bacteria. A key assumption is that a small volume of water taken from under the ball valve (where there is easy access to the stored water) will be representative of the entire tank. To test the reliability of this measure, domestic water samples taken from different locations of selected tanks in London properties between November 2015 and July 2016 were analysed for TVCs, Pseudomonas and Legionella at an accredited laboratory, according to regulatory requirements. Out of ~6000 tanks surveyed, only 15 were selected based on the ability to take a water sample from the normal sampling hatch (located above the ball valve) and from the far end of the tank (usually requiring disassembly of the tank lid with risk of structural damage), and permission being granted by the site manager to undertake the additional investigation and sampling. Despite seasonal differences in water temperature, we found 100% compliance at the ball valve end. In contrast, 40% of the tanks exceeded the regulatory threshold for temperature at the far end of the tank in the summer months. Consequently, 20% of the tanks surveyed failed to trigger appropriate regulatory action based on microbiological analyses of the water sample taken under the ball valve compared to the far end sample using present-day standards. These data show that typical water samples collected for routine monitoring may often underestimate the microbiological status of the water entering the building, thereby increasing the risk of exposure to water bourne pathogens with potential public health implications. We propose that water storage tanks should be redesigned to allow access to the far end of tanks for routine monitoring purposes, and that water samples used to ascertain the regulatory compliance of stored water in tanks should be taken at the point at which water is abstracted for use in the building.
Inhalation of aerosols containing Legionella pneumophila, a water-borne bacteria commonly found in natural and manmade water systems, is the main causative agent of Legionnaires' disease (LD). Approximately 10-15% of all reported cases of LD result in fatality, with susceptibility to the disease being higher in immunosuppressed patients, men over 45 years of age, alcoholics, smokers and individuals with underlying diseases. The World Health Organisation (WHO), European Centre for Disease Prevention and Control (ECDC) and The United Kingdom (UK) Health and Safety Executive (HSE) have implemented a strict code of practice and guidelines to minimise the risk of the public from contracting LD. This paper provides a critical review of these three published guidelines. Evidence suggests that the current detection methods for Legionella, by culture and quantitative polymerase chain reaction (qPCR), show large disparities in the detection and quantification of bacteria in water samples, raising concerns about the reliability of measures needed to safeguard public health. Moreover, a survey of 20 residential building complexes in different London boroughs highlights the need for a review of remedial action recommendations and a more inclusive risk assessment strategy that protects 'at risk' people in society.
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