Several steps must be taken in New York and beyond to reverse the increasing trend in Legionnaires’ disease.

  1. Maintain an adequate disinfectant residual at all points in the public water distribution system.
    A higher free chlorine residual, maintained throughout the distribution system, could effectively limit growth of microbes—including biofilm microbes such as Legionella and other pathogens—in the distribution system. This level requires a number of strategies and considerations. Simply increasing chlorine at the distribution entry point may result in compliance issues with
    disinfection by-products.

    1. a) Improve drinking water treatment to reduce organic carbon content. Organic carbon reduction requirements of the Safe Drinking Water Act (SDWA) are frequently violated due to confusion over reporting, lack of enforcement, and scarcity of funding necessary to implement appropriate treatment. These organic nutrients react with disinfectants to form potentially hazardous disinfection by-products, extinguishing the biocidal effect of the disinfectant in the process.
    2. b) Establish chlorine booster stations to reduce the necessary increase at the entry point.
    3. c) Reduce water age (water residence time in the distribution system) by flushing systems, including water storage tanks. High water age is associated with low disinfectant residual.
  2. Monitor water quality from the public drinking water supply and distribution system.
    1. a) Require community alerts from the public utility to changes in water supply, planned work, or disruptions to water systems which may release high levels of bacteria into the water.
    2. b) Regularly test disinfectant levels throughout the drinking water distribution system. Include dead ends and downstream of tanks. Initiate investigation when the required concentration cannot be maintained.
    3. c) Test drinking water for Legionella bacteria prior to it entering a building.
    4. d) Consider surface swabs for biofilm bacteria testing when lines are open for maintenance.
  3. Increase infrastructure investment.
    Governor Andrew Cuomo recently announced during his State of the State address that New York State would be committing two billion dollars to protect drinking water quality. This provides for great opportunity to have a real impact on preventing Legionnaires’ disease as the issue of waterborne pathogen growth in our water systems begins at the treatment plant. Investments in treatment plant upgrades to reduce organic carbon in finished water are necessary to meet water safety goals. These problems are compounded by corrosion and water main breaks in the distribution system. The poor state of water distribution networks is well-known. Many pipes and mains are nearing the end of their service life and require replacement.
  4. Investigate all cases of legionellosis using investigative tools for single cases and outbreaks already established by the CDC.1
    The CDC investigation tools call for all potential exposures to be evaluated. Outbreaks are relatively rare and offer an excellent opportunity to increase our scientific understanding of Legionella exposure and dose. In the case of community outbreaks which span multiple buildings, traditional epidemiology frequently causes investigators to disregard sections of the protocol and exclude community water systems as a potential source. The body of evidence for widespread distribution of Legionella from the public water system has grown sufficiently for this mode of exposure to be properly investigated. Thorough use of CDC investigation protocols in outbreaks, including comprehensive water sampling and testing for Legionella, will provide researchers, policy makers, and the public with the best possible data allowing for informed decisions.
  5. Positively identify the source of Legionella bacteria after comprehensive investigation.
    It is not sufficient to identify a single water source which contains genetically identical bacteria to patient isolates. Infectious strains of Legionella are endemic to many water distribution systems. If the water supply is colonized then many buildings served by that water supply will also be colonized. Ending an investigation prematurely, such as what happened in New York City, leaves the public at risk.
  6. Manage building water systems according to best practices.
    Critical water quality improvements will take time. Building owners and managers are encouraged to follow best practices related to water management in their buildings. ASHRAE Standard 188 and the CDC Water Management Toolkit are useful references.2,3


2ANSI/ASHRAE Standard 188-2015. Legionellosis: Risk Management for Building Water Systems. Retrieved from

3CDC. Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings. Retrieved from