MOVEMENT PATHWAYS OF NON-TUBERCULOUS MYCOBACTERIUM THROUGH SURFACE AND GROUND WATERS, HAWAI’I USA

Although uncommon, nontuberculous mycobacterial (NTM) pulmonary infection in the Hawaiian Islands has a relatively high incidence and mortality compared to the mainland U.S. Immune-compromised individuals are at particular risk. Prior studies indicate that clinically-significant NTM taxa are common in garden soils and home-plumbing biofilms. As a result, this study examines the environmental (geological, hydrological, and atmospheric) factors and routes by which NTM patients may become infected. This includes the inhalation of NTM attached to dust particles as well as micro-droplets from infected home plumbing systems supplied by groundwater.

Clinically-relevant NTM species were identified by culturing and DNA sequencing of Hawai’i streams and well waters. As NTM are extremely hydrophobic, they strongly prefer to attach to mineral surfaces. The mineralogy and surface chemistry of suspended sediment in streams, soils, and rock scrapings suggest that NTM may attach to mineral surfaces, especially Fe-oxides/hydroxides, and be transported as particles from losing streams to the aquifer on time-scales of minutes to days.

Within the aquifer, groundwater flow models indicate that water may be drawn into production wells on time scales (months) that permit NTM to survive and enter domestic water supplies. These processes depend on the presence of interconnected fracture networks with sufficient aperture to preclude complete subsurface auto filtration. It seems likely that NTM-mineral colloid pairs will readily enter the aquifer based on empirical observations of stream losses and response rates of groundwater elevations to surface water flows. Furthermore, primary porosity and permeability in basalt lavas is controlled by vesicles and cooling fractures. Basalt shrinks by ~2.5% upon cooling, creating joint systems with apertures of up to several mm.

The common occurrence of NTM in and around streams, in addition to wells, implies that the natural and built environments are capable of introducing NTM into domestic water supplies via groundwater withdrawals. As NTM are resistant to chlorination, this may produce a persistent source of NTM infection to individuals with compromised immune systems through the presence of NTM-laden biofilms in home plumbing.

The mineralogy (sensu lato) of Hawaiian dust also suggests an additional route of infection. Construction on the dry parts of the islands may provide constant sources NTM-laden dust to be inhaled and cause disease.