March 2019 • 8=:7+5 80 7>3:876/7<+5 /+5<2 9 which includes measurement of water quality parameters (i.e., disinfectant levels, pH, tem- perature) and water sampling for Legionella , can help identify factors that can lead to Le- gionella amplification and transmission. Trained environmental health special- ists with knowledge of industry standards are needed to evaluate facility water system maintenance procedures, develop and im- plement Legionella environmental sampling plans, measure water quality parameters, advise on Legionella remediation options (i.e., hyperchlorination or superheating and flushing), and provide technical direction for the development of a water management program. Environmental health specialists can also use fundamental industrial hygiene principles such as engineering controls, work practice modifications, and adminis- trative operations to understand and guide water management interventions. We describe an LD outbreak associated with a Missouri hotel, the initial public health in- vestigation, and the subsequent comprehen- sive environmental assessment, underscoring the need for environmental health specialists trained in current industry standards to rec- ommend control efforts and support develop- ment of a water management program to re- duce the risk of future LD cases. Methods Initial Outbreak Investigation In April and June 2015, two LD cases con- firmed by Legionella urinary antigen test- ing were reported among persons who had stayed in the same Missouri hotel. Local public health officials conducted an envi- ronmental assessment of all water systems; however, because spas are a common source of hotel-related outbreaks (Dooling et al., 2015), control efforts initially were focused solely on disinfection of the pool and spa. At the time, water samples were not collected from other building water systems for Legio- nella testing. In October 2015, a third guest at the same hotel died of LD, prompting further investi- gation by state public health officials. After review of the initial environmental assess- ment, a total of five environmental samples were collected from the pool, spa, spa filter, water heater, and a tank associated with the heating, ventilation, and air-conditioning (HVAC) system. Legionella testing of these samples at an Environmental Legionella Iso- lation Techniques Evaluation (ELITE) mem- ber laboratory (www.cdc.gov/legionella/elite. html) was negative. The state health depart- ment requested CDC’s assistance for the envi- ronmental investigation. Epi-Aid Environmental Assessment In November 2015, CDC epidemiology and laboratory staff joined state and local epide- miology and environmental health staff to interview the building owner, maintenance employees, and pool/spa contractors. They performed a detailed environmental assess- ment of the hotel, including a review of • facility blueprints and survey of the facility (i.e., occupancy rates, number of buildings and floors); • sources of water (i.e., potable water, spa, cooling towers, decorative fountains); premise plumbing system components (i.e., where and how water flows through buildings [water heaters, storage tanks, and point-of-use sites such as showers and sink fixtures]); • changes in municipal disinfectant use; • water system maintenance records; • water management program; • water quality parameters; and • factors external to the building such as construction and water main breaks. The team identified potential sites of Legio- nella amplification and transmission using a standardized environmental assessment form (CDC, 2015) and hand-drawn water system diagrams provided by hotel staff. Epi-Aid Water Quality Measurement and Environmental Sampling During the assessment, the team examined water quality parameters (e.g., pH, tempera- ture, disinfectant levels) at sites near the water entry into the building (proximal) and along the water distribution system at point-of-use (medial and distal) to identify areas of risk for Legionella growth. We noted all aerosol-generating devices (e.g., show- ers, faucets, spa) that represented potential points of exposure and measured the above- mentioned water parameters. Because of the recent change in municipal disinfection (from chlorine to monochloramine), total chlorine levels were measured at selected sites (CDC, 2018a; Fields, 1996; U.S. Envi- ronmental Protection Agency, Office of Wa- ter, 2016). Using knowledge of the facility’s water distribution and water quality parameters, along with epidemiologic data, the team de- veloped a water sampling plan for Legionella that included sites throughout the hot water distribution systems and associated heaters, storage tanks, and hot water returns (CDC, 2018a; Kozak, Lucas, &Winchell, 2013). Im- properly maintained spa filters can serve as a source of Legionella growth; therefore, we also obtained biofilm swabs of filter housings identified in the spa and pools (CDC, 2018b; Garrison et al., 2016). Water samples and biofilm swabs were processed at CDC’s Legionella Laboratory. Legionella isolates were characterized by se- rogroup and sequence typing (Lück, Fry, Hel- big, Jarraud, & Harrison, 2013). Results Epi-Aid Environmental Assessment The hotel’s two buildings were constructed in 1989 and in February–August 2015, respec- tively, and are connected independently to the municipal water supply. No interruptions to the potable water system were reported dur- ing the more recent construction. The assess- ment focused on the older building, where all guest rooms possibly associated with LD cases were located. This building had 3 floors with 79 guest rooms arranged around a cen- tral atrium overlooking an unenclosed pool and spa. A 4.5-ft wall separated the pool and spa from the elevator, front desk, and sur- rounding rooms. The municipal water facility used a chlo- rine disinfection system until August 2015 but changed to monochloramine disinfection in September 2015 to meet federal drinking water standards. Heated water from the wa- ter heater was stored in a hot water storage tank and traveled through riser pipes and a recirculating loop to deliver and collect wa- ter from the guest room sinks and showers/ bathtubs on each floor. Thermostatic mixing valves were located on sinks and showers of the guest rooms. The potable water system relied on municipal disinfection. By design, the HVAC system did not aerosolize water (i.e., it was not a cooling tower or evapora- tive condenser) and thus likely did not pose a risk for Legionella transmission.