Recent clusters of Legionnaires’ disease in New York City and Ohio are drawing renewed attention to the bacterial risk in building water systems. In NYC’s Central Harlem, health officials have reported 67 cases and three deaths since late July. Eleven cooling towers in the affected ZIP codes initially tested positive for Legionella and have since undergone remediation.
Ohio has also seen elevated activity, with 311 cases of legionellosis reported statewide so far this year. Southwest Ohio alone recorded 40 cases through July, according to regional health data.
Legionnaires’ disease is a severe pneumonia caused by inhaling aerosolized water containing Legionella bacteria. Common sources include cooling towers, hot water systems, decorative fountains, whirlpools, and humidifiers. The disease cannot be spread person-to-person and is treatable with antibiotics, but it can be fatal, particularly for adults over 50, smokers, and those with chronic lung conditions or weakened immune systems.
Health experts point to warmer late-summer temperatures, heavy rainfall, and flooding as factors that can boost bacterial growth in water systems. Storms and floods can mobilize biofilms—microbial layers where Legionella thrives—causing spikes in bacterial loads and increasing colonization risks. Aging U.S. water infrastructure and fluctuating building occupancy also contribute to the challenge.
In NYC, Acting Health Commissioner Dr. Michelle Morse is urging anyone in affected ZIP codes with flu-like symptoms—fever, cough, chills, muscle aches, or shortness of breath—to seek medical evaluation immediately. Early diagnosis is critical for effective treatment.
CDC data show a steady rise in Legionnaires’ disease cases since the early 2000s, interrupted only by a temporary dip during the early COVID-19 pandemic. Outbreak investigations often identify building water systems as the contamination source, with healthcare, hospitality, and large residential facilities being frequent settings.
Building operators play a critical role in prevention by maintaining robust water management programs, monitoring system conditions after severe weather, and addressing issues like stagnation or disinfectant loss before they escalate. The recent outbreaks in NYC and Ohio highlight how quickly Legionella can become a public health concern, especially in aging systems and during seasonal risk periods. Proactive oversight, clear communication, and swift corrective action remain the strongest defenses against future cases.
