Water Technology: Is monochloramine treatment versus chlorine treatment more effective at controlling the spread of Legionella?

Joseph Cotruvo: There are several studies that demonstrate that chloramine use reduces the Legionella concentrations in distribution system water. Apparently, due to their low chemical reactivity, chloramines are capable of penetrating deeper into biofilms where the Legionella proliferate. So, even though they are less potent disinfectants they may be more effective in this environment.

Water Technology: Why are hospitals so susceptible to Legionella outbreaks? And what are some ways of killing the bacteria?

Joseph Cotruvo: Hospitals appear to be more susceptible to Legionella outbreaks because they house a higher risk population in a more concentrated environment where diagnosis is more likely. Thus, it might also partly mean that cases are more readily identified in hospitals. However, there are plenty of high risk people in the community. These would be older people, people with immune deficiencies, smokers and people under outpatient medical treatment who have greater susceptibility. Many cases are travel associated (hotels, cruise ships). They are more widely distributed so that makes it more difficult to detect and diagnose cases and attribute them to a particular cause.

Inhalation of contaminated aerosols is the primary route of infection. It is known that Legionella can proliferate in warm water environments where the temperature is in the 25-50°C temperature range. This could include hot water systems, hot tubs, shower heads and AC cooling water. CDC (http://www.cdc.gov/legionella/patient_facts.htm) (http://www.cdc.gov/legionella/faq.htm) and WHO recommend that water temperatures be maintained outside of this range. However, as temperatures increase at about 55°C and above the risk of scalding increases, older people and children are at greater risk of scalding.

Contaminated plumbing systems are decontaminated by heat shock treatment (up to 70°C) and shock (high dose) chlorination up to 2000 ppm (http://www.ijic.info/article/download/3688/2811), or chlorine dioxide. Some claim that silver/hydrogen peroxide is effective as a shock treatment.

Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He holds a Ph.D. in Physical Organic Chemistry and is a member of the World Health Organization's Guidelines for Drinking-water Quality Committee and expert advisory groups on drinking water quality, desalination, wastewater and water reuse. He is a former director of the USEPA Drinking Water Standards Division.