As a third individual succumbed to Legionnaires’ disease in New York City this month, public health officials announced their belief that the bacterial source of the outbreak has been eradicated. Investigations revealed the presence of legionella bacteria, both living and deceased, in 76 cooling towers across buildings on the Upper East Side, including museums, private schools, and luxury apartment buildings.
The city mandated that owners of these affected buildings drain, clean, and disinfect their cooling towers. Remediation efforts were reported as complete by July 18. By this date, 74 individuals had been diagnosed with the illness. While eight people remained hospitalized with the disease the following day, the city’s health department indicated a decline in newly diagnosed cases.
Though this specific outbreak may seem localized, Legionnaires’ disease cases have been on a consistent rise nationwide in recent years. Here are four key points to understand about this serious bacterial pneumonia:
1. Legionnaires’ Disease is a Severe Pneumonia Transmitted Through Water Vapor.
The most common way Legionnaires’ disease spreads is when a person inhales mist or water vapor contaminated with legionella bacteria, which then infects the lungs. This mist can originate from sources like showers or sinks. The disease does not spread directly from person to person. Ingesting water containing the bacteria will not cause infection. However, infection can occur if contaminated water is aspirated, meaning it enters the lungs during coughing or choking while drinking.
While legionella bacteria naturally exist in freshwater environments like lakes and soil, human-made water systems where the bacteria can thrive present the most significant risk of infection. Numerous sources have been linked to Legionnaires’ disease cases, including hot tubs, water heaters, humidifiers, swimming pools, and even medical equipment like ventilators. Large building air conditioning systems that utilize cooling towers can also be a source of outbreaks. If legionella proliferates in the water within these towers, it can be dispersed throughout the building’s air supply. Smaller home and car air conditioning units are not typically sources of outbreaks as they do not rely on water.
2. Individuals Over 50, Smokers, and Those with Compromised Immune Systems Face Higher Risk.
While anyone can contract Legionnaires’ disease, certain factors increase the likelihood of developing the illness after exposure to legionella bacteria. Those over 50, individuals with weakened immune systems, current or former smokers, and people with chronic respiratory conditions, emphysema, diabetes, or cancer are at greater risk of severe illness and complications. Studies have also indicated higher rates of Legionnaires’ disease among Black individuals and those with lower incomes. The disease can lead to life-threatening complications such as respiratory failure, heart inflammation, and kidney failure. Antibiotics are typically prescribed to treat Legionnaires’ disease and are usually effective, leading to full recovery for most patients, especially with early intervention.
3. Legionnaires’ Disease Cases Have Steadily Increased Since the Early 2000s.
Data indicates a continuous rise in the annual incidence of Legionnaires’ disease in the U.S. since the turn of the millennium. While cases saw a peak in 2018 and a temporary dip during the initial phase of the COVID-19 pandemic, they have since resurged and have not returned to the lower levels observed in the early to mid-2000s. The precise reasons for this sustained increase are not fully understood, but contributing factors may include climate change. Experts anticipate an increase in waterborne illnesses due to climate change-induced shifts in temperature, heavy rainfall, flooding, and drought. Research suggests that rising temperatures are linked to a greater risk of Legionnaires’ disease. Additionally, increased precipitation, along with higher temperatures and humidity, has been associated with an elevated risk, although the impact of the latter two factors is considered more moderate. A potential, though less direct, factor could be declining air pollution. A study published in 2024 suggested a correlation between the rise in Legionnaires’ disease cases and a decrease in acidic sulfur dioxide pollution in the U.S. The reasoning is that a more acidic environment is less conducive to legionella bacteria, meaning reduced sulfur dioxide pollution could inadvertently contribute to higher case numbers.
4. The First Documented Outbreak Sparked Conspiracy Theories.
The illness was first identified following a significant outbreak in July 1976 that garnered national attention. All affected individuals had attended the American Legion Convention in Philadelphia and stayed at the same hotel. Within a week of the convention’s conclusion, over 200 people became ill, and 34 died. The Centers for Disease Control and Prevention (CDC) dispatched a team to investigate, but the cause remained elusive for a period. The lack of immediate answers fueled speculation and conspiracy theories. Given the nation’s bicentennial celebrations and the presence of many veterans among those affected, some theorized foreign involvement, while others pointed fingers at activists opposing the Vietnam War. It took several months, until January 1977, for scientists to isolate the bacteria responsible. The bacteria was subsequently named legionella, and the disease it causes, Legionnaires’ disease, both in honor of this pivotal outbreak among American Legion members.