The contamination of drinking water outlets with waterborne pathogens is a growing problem that affects both public and private infrastructure. Water outlets and pipelines can be contaminated by OPPPs present in the source water (such as L. pneumophila
) or alternatively, at the outlet by individuals washing their hands (such as P. aeruginosa
]. Once contamination occurs, these pathogens adhere to surfaces and develop or are incorporated into biofilms, which help protect the cells from physical and chemical disinfection [46
]. Exposure to these pathogens can occur via ingestion or aspiration of contaminated water during bathing, and drinking, or inhalation of contaminated aerosols from water outlets such as shower heads [42
]. This can cause a range of infections in vulnerable people including respiratory, skin and soft tissue, gastrointestinal, blood, and neurological pathologies [17
Emerging evidence suggests that the number of OPPPs in drinking water is increasing and correlates with the number of individuals vulnerable to infections caused by these pathogens [46
]. In the USA, Legionella
spp. has been identified as the leading cause of drinking water disease outbreaks [47
]. With the annual economic cost of infections requiring hospitalizations estimated at $
430 million for Legionella
spp. and $
425 million for NTM [48
]. One of the biggest challenges facing regulators controlling these pathogens is the difficulties associated with quantifying the associated risks of infection [49
]. Without attention to these emerging issues, their public health impact could be underestimated or overlooked compared to comparable or lesser hazards for which the risks can be more easily quantified.
Non-Tuberculous Mycobacterium (NTM)
NTM are a particularly pervasive group among the opportunistic bacterial pathogens, often resulting in a slowly progressive and destructive disease which can affect both immune compromised and otherwise healthy individuals [50
]. Unlike other OPPPs, they can commonly infect children, which makes them an interesting case study to consider in relation to the Victorian Schools situation. In healthy children, NTM can cause cervical lymphadenitis (infection of lymph nodes) which can require surgical excision or antibiotic therapy. Both treatments have complications including reoccurrences of infection [52
]. They are also a common cause of pulmonary infection in children with cystic fibrosis [53
]. There has been a concerning worldwide increase in the incidence of NTM infections. For example, in Wales and Northern Ireland, NTM cases increased from 5.6 per 100,000 population in 2007 to 7.6 per 100,000 persons in 2012 [54
]. In Germany, cases of pulmonary NTM disease increased from 2.3 per 100,000 persons to 3.3 per 100,000 persons from 2009–2014 [55
]. In the U.S. the prevalence of NTM disease in the general population was estimated at 1.8 per 100,000 persons in the 1980s [56
]. This increased to between 4.1 and 7.2 cases per 100,000 persons [57
] by the early 2000s.
In Australia, cases of NTM infection are not notifiable in every state or territory, and therefore it is difficult to obtain accurate current records of the rate of NTM infections on a national level. In 2000, a survey of NTM isolated from patients estimated that the national level of NTM infection to be between 5.6 (South Australia) and 71.3 (Northern Territory) cases per 100,000 population, with the national average being 7.5 per 100,000 persons [60
]. However, where NTM infections remain a notifiable disease, cases of NTM infection are on the rise, mirroring trends seen internationally. In Queensland, cases have increased steadily in recent years, from 1093 in 2014, 1208 in 2015, 1309 in 2016, 1478 in 2017, and 1433 in 2018 (Figure 3
). In 2018, this equated to an infection rate of 28.8 per 100,000 population. In Queensland, publicly available data exists for both the number of reported NTM infections, as well as the number of cases of non-occupational related elevated BLL (≥5 µg/dL) for the years 2014 and 2015 (Figure 4
). The rate of NTM infections for those years are significantly greater than the cases of elevated BLL that may require further investigation.
Sources of NTM may be water, or soil and dust [17
], however recent evidence has pointed to plumbing materials and water supplies as being a major contributor to NTM cases. A study in the U.S of 40 households and buildings in 25 different states over a two year period found 78% of water samples taken from drinking water outlets were contaminated with NTM [11
]. In Australia, MAC, the most common NTM causing disease, has been found in both chlorine and chloramine disinfected municipal drinking water distribution pipelines [61
]. Studies have identified that within the water plumbing system, opportunistic bacterial pathogen contamination is far more prevalent at the end points of the system (i.e. taps, aerators, shower heads) than in the broader pipe plumbing infrastructure [62
]), thus providing a reservoir for the bacterial pathogens directly at the user interface.
While the presence of bacterial contamination of the water outlet does not guarantee users will become infected, it does provide the direct avenue for opportunistic bacteria to infect vulnerable users, such as those with already compromised immune systems through other sickness or disease, the young, and the old. In fact, a direct connection between opportunistic bacterial contamination of drinking water outlets and infections in patients has been established. In Australia, a 2013 study tested the contamination of household water sources for NTM contamination, and compared the genetic profile of the isolated organisms to that isolated from the patient [16
]. Therein pathogenic NTM was isolated from 96% of homes (19 of 20 households), where samples were taken from the kitchen, bathroom and shower taps, rainwater tanks, swimming pools, and shower heads. In 35% of cases, the NTM bacteria found in the home was the same as that isolated from the infected patient. A similar study undertaken in the U.S showed that 41% of homes of persons infected with NTM had NTM bacteria present at their drinking water outlets. Furthermore, the NTM isolated from their drinking water plumbing system were identical to that from the infected person [12
]. In another study [63
], samples taken from showerheads by citizen scientists in the US and Europe were tested for the presence of NTM, with the goal of building a geographic pattern of NTM distribution in different drinking water supplies. Interestingly, hotspot regions were identified in the U.S, where regions presenting a high incidence of NTM contamination of drinking water outlets coincided with regions where NTM infections were most prevalent.