AUTHOR=Denissen Julia K. , Reyneke Brandon , Waso Monique , Khan Sehaam , Khan Wesaal 

TITLE=Human Pathogenic Bacteria Detected in Rainwater: Risk Assessment and Correlation to Microbial Source Tracking Markers and Traditional Indicators

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.659784

DOI=10.3389/fmicb.2021.659784

ISSN=1664-302X

ABSTRACT=<p>Roof-harvested rainwater (RHRW) was investigated for the presence of the human pathogenic bacteria <italic>Mycobacterium tuberculosis</italic> (<italic>M. tuberculosis</italic>), <italic>Yersinia</italic> spp. and <italic>Listeria monocytogenes</italic> (<italic>L. monocytogenes</italic>). While <italic>Yersinia</italic> spp. were detected in 92% (<italic>n</italic> = 25) of the RHRW samples, and <italic>L. monocytogenes</italic> and <italic>M. tuberculosis</italic> were detected in 100% (<italic>n</italic> = 25) of the samples, a significantly higher mean concentration (1.4 × 10<sup>3</sup> cells/100 mL) was recorded for <italic>L. monocytogenes</italic> over the sampling period. As the identification of appropriate water quality indicators is crucial to ensure access to safe water sources, correlation of the pathogens to traditional indicator organisms [<italic>Escherichia coli</italic> (<italic>E. coli</italic>) and <italic>Enterococcus</italic> spp.] and microbial source tracking (MST) markers (<italic>Bacteroides</italic> HF183, adenovirus and Lachnospiraceae) was conducted. A significant positive correlation was then recorded for <italic>E. coli</italic> versus <italic>L. monocytogenes</italic> (<italic>r</italic> = 0.6738; <italic>p</italic> = 0.000), and <italic>Enterococcus</italic> spp. versus the <italic>Bacteroides</italic> HF183 marker (<italic>r</italic> = 0.4071; <italic>p</italic> = 0.043), while a significant negative correlation was observed for <italic>M. tuberculosis</italic> versus the <italic>Bacteroides</italic> HF183 marker (<italic>r</italic> = −0.4558; <italic>p</italic> = 0.022). Quantitative microbial risk assessment indicated that the mean annual risk of infection posed by <italic>L. monocytogenes</italic> in the RHRW samples exceeded the annual infection risk benchmark limit (1 × 10<sup>–4</sup> infections per person per year) for intentional drinking (∼10<sup>–4</sup>). In comparison, the mean annual risk of infection posed by <italic>E. coli</italic> was exceeded for intentional drinking (∼10<sup>–1</sup>), accidental consumption (∼10<sup>–3</sup>) and cleaning of the home (∼10<sup>–3</sup>). However, while the risk posed by <italic>M. tuberculosis</italic> for the two relevant exposure scenarios [garden hosing (∼10<sup>–5</sup>) and washing laundry by hand (∼10<sup>–5</sup>)] was below the benchmark limit, the risk posed by adenovirus for garden hosing (∼10<sup>–3</sup>) and washing laundry by hand (∼10<sup>–3</sup>) exceeded the benchmark limit. Thus, while the correlation analysis confirms that traditional indicators and MST markers should be used in combination to accurately monitor the pathogen-associated risk linked to the utilisation of RHRW, the integration of QMRA offers a more site-specific approach to monitor and estimate the human health risks associated with the use of RHRW.</p>