Geological and Geochemical Controls on Non-Tuberculous Mycobacterium Transmission: Examples from Hawaii

• Main Author: Robinson, Schuyler Thomas
• Format: Others
• Published: BYU ScholarsArchive 2019
• Subjects: Mycobacteria; soil chemistry; logistic regression; particle tracking; Oahu; Kilauea; NTM; HVO; groundwater model; disease; PCA; NMDS
• Online Access: https://scholarsarchive.byu.edu/etd/8558; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=9558&context=etd

The opportunistic environmental microbes, non-tuberculous Mycobacterium (NTM), pose an increasing risk of disease and death in both immunodeficient and immunocompetent individuals in the USA and across the world. NTM lung disease is particularly prevalent in Hawaii, although the modes of NTM acquisition and transport in Hawaii are not fully understood. This study evaluated 149 soil and 50 water samples across the Hawaiian Islands to determine geochemical factors controlling NTM. Non-metric multidimensional scaling (NMDS) and principal component analyses (PCA) of modern soils show variables such as Total Organic Carbon (TOC), pH, P, mafic silicate minerals, and Pb seem to control NTM presence and transition metals and oxides such as TiO2, Zr, and Nb seem to control the absence perhaps due to toxicity. Logistic regression modeling coupled with Kolmogorov-Smirnov testing supported that TOC and P could be used to explain the probability of NTM presence in modern soils. Kolmogorov-Smirnov, non-metric multidimensional scaling, and principal components analysis results suggest poor predictability of NTM presence in soils when evaluating mineralogy alone. The same statistical methods indicated that transition metals appeared to control NTM presence in stream water and major cations and anions seemed to control NTM absence. However, additional bacterial stream data is needed to strengthen this finding. Additionally, an Oahu source water assessment and protection groundwater model was refined by including stream discharge data, including losses to the aquifer. NTM inhabits many environmental niches, although little is understood regarding the transport of NTM from the environment to indoor plumbing. However, transport from surface water to water-supply aquifers is likely important. This study analyzes groundwater flow from stream losses as a mechanism of NTM transport to water supplies. An updated MODFLOW groundwater model was developed for the north-east Oahu, Waimea River drainage. Results show hundreds of meters of lateral and tens of meters of vertical transport of NTM in 1-3 months. Additionally, geochemical modeling with Geochemist’s Workbench showed Fe oxy/hydroxides oversaturated in 100% of streams. Fe oxy/hydroxide affixed to NTM would potentially satisfy NTM’s preference for attachment and allow for colloidal transport through the aquifer.