1.1 Background to the Study
Water is an essential substance in human life as it is used for various purposes sucg as drunking washing cooking. Human noroviruses cause the most gastrointestinal illness in all regions of the world, with the vast majority thought to be acquired via person-to-person and then by food (Ahmed et al., 2014) given the predominance of genogroup II strains implicated. In waterborne cases, genogroup I is normally implicated (Mathew et al., 2012), presumably due to increased environmental robustness. An interesting finding with human noroviruses and the second most common cause of gastrointestinal illness, rotavirus (although greatly diminishing due to childhood vaccination programs), is the need for certain histo-blood group antigen (HBGA) receptors for these pathogens to bind to target cells (Tan and Viang, 2014). Not only do certain gut bacteria have these HBGA binding sites but these bacteria may also facilitate infection, as recently demonstrated with human B cells (Jones et al., 2014). Therefore, one’s gut microbiome and blood group impact the likelihood of infection. Furthermore, there is now optimism that a routine cell culture system for human noroviruses may be developed, which would be of particular value to the water-treatment industry. Non-human, culturable noroviruses, such as murine noroviruses among others, are used as surrogates for treatment performance (inactivation studies) but there is limited understanding of the validity of these surrogates for any human norovirus genogroup or mode of inactivation (LI et al.,2014; Cromeans et al., 2014).
The classic waterborne enteric pathogens include Vibrio cholerae (serogroups O1 and O139, causing cholera), Salmonella enterica (subsp. enterica ser. Typhi, causing typhoid), and Shigella spp. (four species causing dysentery), which have largely been controlled by water treatment/disinfection and are therefore rarely an issue via drinking water in developed regions. However, person-to-person and foodborne spread maintains Shigella sonnei within the sewage of developed regions, along with closely-related shiga toxin and verotoxin-producing E. coli, and pathogenic species of Campylobacter, Salmonella, Arcobacter, Helicobacter and Yersinia. An emerging issue is that of AMR, which may occur within any of the bacterial members but is noted here by example for E. coli in well waters associated with animal production (Coleman et al., 2013). These AMR genes may horizontally transfer between commensal and enteric pathogenic bacteria, and present a higher risk due to antimicrobial treatment failures (Ashbolt et al., 2013). Within healthcare facilities, there is also a considerable health burden due to the prevalence of AMR Pseudomonas aeruginosa and Clostridium difficile; with the latter being a spore-former it may persist in sewage and river waters and eventually make its way to drinking waters, and AMR-P. aeruginosa may grow post-water treatment.