Rates of Lung Disease May Be Influenced by Mycobacterial Colonization in Municipal Water

Nontuberculosis mycobacteria are opportunistic human pathogens and several species, including members of the Mycobacterium avium complex (MAC), can trigger difficult-to-treat and life-threatening pulmonary infections. Therefore, determining sources of MAC infections are a critical part of disease prevention and control.

In a new study published in the US Centers for Disease Control and Prevention (CDC)’s Emerging Infectious Diseases journal, investigators assessed MAC colonization of household plumbing in suburban Philadelphia, an area identified as 1 of 7 counties in the United States with a high risk for MAC lung disease.

“Proof of an environmental source of M avium has broad implications regarding prevention of recurrent infection in existing patients as well as prevention of new disease in susceptible persons,” the investigators wrote in the research letter.

The team prospectively identified and randomly selected study participants from female patients with newly diagnosed MAC pulmonary infection at Lankenau Medical Center in Montgomery County, Pennsylvania, between 2010 and 2012.

MAC respiratory isolates were recovered from 26 patients during the study period. All 26 patients had nodular bronchiectasis, which was confirmed by computed tomography, and also MAC lung disease as defined by the American Thoracic Society and Infectious Diseases Society of America criteria. The investigators collected household biofilm isolates from all 26 participant’s households.

The investigators identified 3 species of MAC: M avium subsp. Hominissuis (21 patients of 26 patients, 80.8%), M intracellulare (3 of 26, 11.5%), and M chimaera (2 of 26, 7.7%).

At enrollment, the median age of patients was 77 years (44-90 years), 97% (25/26) were white, 42% (11/26) were former smokers, and 88% (23/26) had no previous or co-occurring lung disease other than bronchiectasis.

The investigators also included 11 geographically matched individuals for controls, all of whom were healthy patients with negative MAC culture and who submitted samples from their homes, which shared municipal water systems with the study group.

The investigators used variable-number tandem-repeat genotyping and whole-genome sequencing along with core genome single-nucleotide variant analysis to compare M avium from household plumbing with M avium isolates from 30 (81.1%) of 37 participant households, including 19 (90.5%) of 21 M avium patient households.

For 11 of 21 patients (52.4%) with M avium-related disease, isolates recovered from their respiratory and household samples were of the same genotype.

Within the same community 18 of 21 M avium (85.7%) of respiratory isolates genotypically matched household plumbing isolates Further, 6 predominant genotypes were recovered across multiple households and respiratory specimens. All of which implies that M avium colonizing municipal water and household plumbing may be a substantial source of MAC pulmonary infection.

“Our study identified household plumbing biofilms as a reservoir for M avium and suggests that local rates of MAC lung disease may be influenced by mycobacterial colonization of municipal water,” the authors wrote in the research letter.

The authors explain further, that based on these data, they cannot rule out other reservoirs for MAC, including soil and dust, but “recovery of M avium from those sites and subsequent matches to patient isolates have been minimal.”

In explaining how colonization is possible, the investigators explain that the innate resistance to chlorine and other disinfectants typically used in water treatment provides a survival advantage for M avium over most waterborne pathogens.

Although the M avium strain appears to be more prevalent in this area of Pennsylvania, it is hypothesized that in other geographic regions, the MAC lung disease rate is affected by the prevalence of particular Mycobacterium species.

The investigators note that additional studies are needed to establish effective methods for eliminating environmental reservoirs of M avium and other problematic nontuberculosis mycobacteria.

“Tackling this challenging problem will require engagement of water utility workers, plumbers, environmental scientists, and engineers,” the investigators conclude.