Water Treatment Strategies Vary in Effectiveness Against Bacterial Species Causing Respiratory Infections

Several species of bacteria that can transmit respiratory infections have varying levels of response to the disinfecting agents used in municipal water treatment systems, with no one water disinfection strategy achieving complete microbial control, according to new findings.

Legionella pneumophila and Mycobacterium avium, intracellulare, and abscesses are water-borne bacteria that cause legionellosis and nontuberculous mycobacterial (NTM) lung infections, respectively. Public utility systems disinfect water supplies with chemicals like chlorine and chloramine, but the mycobacterial species are more resistant than L pneumophila, and both types of bacteria can be found in samples of drinking water, according to previous studies.

The current study, published in Applied and Environmental Microbiology, aimed to describe differences in the use of chlorine and chloramine and the relationship between the concentration of these chemicals and the concentration of microbes found in tap water samples.

Researchers analyzed 358 samples collected from taps across the United States that were served by public utilities using chlorine or chloramine to disinfect the water. The found that L pneumophila was detected in 26% of the samples, whereas detection rates for the 3 mycobacterial species ranged from 9% to 22%. They found significantly higher detection rates of M avium (22%; P = .02) and M abscesses (17%; P = .03) in samples that were treated with chloramine.

When analyzing bacterial concentration, they determined that there were significantly fewer L pneumophila cell equivalents per liter in samples from water treated with chloramine than with chlorine (P <.001); this difference remained significant when separately examining samples from cold water lines and hot water lines. There was a lower concentration of M intracellulare in water treated with chlorine than with chloramine when assessing only samples from cold water lines.

The researchers also found higher total chlorine residual (TCIR) concentrations in chloramine- versus chlorine-treated water, and they noted that measurable TCIR was more likely to be present in samples from cold versus hot water lines. In chlorine-treated water, the ratio of samples positive for 1 or more microbe to samples with no pathogens, termed the positive to negative (P:N) ratio, decreased as the TCIR increased, whereas the P:N ratio remained about 1:1 in the chloramine-treated samples regardless of TCIR concentration.

Although laboratory studies have suggested that both chlorine and chloramine are effective in eliminating the studied pathogens, this real-world study found persistent presence of Legionella and Mycobacterium microbes. The results may differ due to uncontrolled factors like the nutrients in biofilm found in potable water systems, the study authors wrote.

Their finding of varying levels of disinfectant effectiveness “may relate to the characteristics of the different source waters (reservoirs, lakes, rivers, etc) that are highly diverse in their chemical composition (eg, concentrations of organic carbon, nitrogen, etc) and physical properties (eg, pH, temperature, etc).”

They concluded that selection of a disinfecting agent for municipal water utilities to prevent legionellosis, NTM infections, and other diseases should be informed by the specific characteristics of the water source and location. Additionally, levels of chlorine and chloramine must be adjusted to preserve the taste and odor of drinking water and avoid skin or eye irritation from overchlorinated water.

Reference

Donohue MJ, Vesper S, Mistry J, Donohue JM. Chlorine and chloramine impact on the detection and quantification of Legionella pneumophila and Mycobacterium species [published online October 11, 2019]. Appl Environ Microbiol. doi: 10.1128/AEM.01942-19.