Environmental Nontuberculous Mycobacteria in the Hawaiian Islands

Abstract

Lung disease caused by nontuberculous mycobacteria (NTM) is an emerging infectious disease of global significance. Epidemiologic studies have shown the Hawaiian Islands have the highest prevalence of NTM lung infections in the United States. However, potential environmental reservoirs and species diversity have not been characterized. In this cross-sectional study, we describe molecular and phylogenetic comparisons of NTM isolated from 172 household plumbing biofilms and soil samples from 62 non-patient households and 15 respiratory specimens. Although non-uniform geographic sampling and availability of patient information were limitations, Mycobacterium chimaera was found to be the dominant species in both environmental and respiratory specimens. In contrast to previous studies from the continental U.S., no Mycobacterium avium was identified. Mycobacterium intracellulare was found only in respiratory specimens and a soil sample. We conclude that Hawai'i's household water sources contain a unique composition of Mycobacterium avium complex (MAC), increasing our appreciation of NTM organisms of pulmonary importance in tropical environments.

Fig 1. Environmental sampling for NTM.

A) Biofilm swabs and soil samples were collected from 62 households on four of eight principal Hawaiian Islands. The numbers and proportions of total households from which NTM were recovered are shown. B) Locations of households sampled in towns across the island of Oahu. Colored triangles indicate sampling sites with biofilm or soil samples that were positive for presence of NTM (red) or negative for NTM (blue). C) The number of NTM species recovered from each household was calculated. Shown are the proportions of households harboring zero NTM species/household, one NTM species/household, two NTM species/household or three different NTM species/household.

Fig 2. Diversity and frequency of NTM species recovered from environmental samples.

A) Phylogenetic analysis was performed from a multiple sequence alignment of partial rpoB sequences to illustrate the distribution of SGM and RGM isolates identified among environmental samples. Bolded names indicate NTM species in which more than one isolate was identified across the sample set. B) Proportions of samples positive for NTM species are shown for households (n = 75) and non-household sites (n = 9).

Fig 3. Household distribution of NTM species.

Proportions of household samples harboring various NTM species are shown. Statistical comparisons between household locations were performed by Fisher’s exact tests (*p = 0.05).

Fig 4. Distributions of rpoB sequence variants detected among Hawaiian Island environmental isolates of M. porcinum, M. abscessus, and M. chelonae compared to type strains.

Sequence variant networks were created based on alignments of partial rpoB gene sequences for: A) M. porcinum (n = 25 total sequences, out of 615 positions) B) M. abscessus (n = 38 total sequences, out of 610 positions) and C) M. chelonae (n = 35 total sequences, out of 613 positions). Pie charts were used to indicate the distribution of isolates from different sources sharing an identical rpoB variant. Colors reflect distinct isolate sources. Hash marks indicate SNP differences between adjacent isolate subgroups. Isolates per rpoB variant (n = X) are specified for each variant occurring in more than one isolate. Type strains are indicated next to their designated variant group and are denoted by superscript “T.”

Fig 5. Distribution of rpoB sequence variants among Hawaiian Island environmental and clinical isolates of M. chimaera compared to type strains.

A sequence variant network was created based on an alignment of partial rpoB gene sequences (n = 103 total sequences, out of 591 positions) including environmental and Oahu clinical isolates. Hash marks indicate SNP differences between adjacent isolate subgroups (circles). Isolates per rpoB variant (n = X) are specified for each observed variant. Type and non-type strain sequences and random clinical isolates from the continental U.S. were included for comparison. The M. chimaera type strain is denoted by superscript “T”.