Legionnaires’ disease outbreak: What to know after fourth death in New York City

How Legionnaires’ disease spreads and why cooling towers are linked to outbreaks

Dr Palleti Siva Karthik Reddy, MBBS, MD, general medicine, FAIG, Consultant physician at Elite Care Clinic, tells indianexpress.com, “Legionnaires’ disease is a serious form of pneumonia caused by Legionella bacteria, which naturally exist in water environments. Infection occurs when a person inhales tiny water droplets containing the bacteria. During community outbreaks, cooling towers are frequently identified as the source because they can generate large amounts of aerosolised water that may spread over a considerable distance.”

Dr Jagadish Hiremath, Public Health Intellectual, adds, “In contrast, drinking tap water is generally not a concern because stomach acid helps neutralise the bacteria, and domestic air conditioners do not typically create the type of aerosol-generating water circulation associated with outbreaks.”

Who is most at risk and when to seek medical attention

“The highest risk is seen among older adults, smokers, people with chronic lung disease, and those with weakened immunity,” says Dr Reddy, adding that early symptoms can resemble influenza and include fever, headache, fatigue, muscle aches, and cough. However, Legionnaires’ disease often progresses to significant breathing difficulty and pneumonia. A persistent high fever, worsening cough, chest discomfort, shortness of breath, or confusion should prompt immediate medical evaluation, particularly in individuals with known risk factors.

“One clue that differentiates Legionnaires’ disease from a routine viral infection is that patients may develop gastrointestinal symptoms such as diarrhoea, nausea, or abdominal discomfort alongside respiratory complaints. Symptoms that rapidly worsen, especially breathlessness, persistent fever, reduced oxygen levels, or altered mental status, require urgent medical assessment and possible hospitalisation,” reveals Dr Hiremath.

Preventing Legionnaires’ disease and understanding outbreak risk

Prevention relies heavily on proper maintenance of water systems. Dr Reddy says that building owners should ensure regular inspection, cleaning, disinfection, and monitoring of cooling towers and large plumbing networks. Public health authorities play a key role in surveillance, testing, and rapid investigation of suspected sources.

For individuals, Dr Reddy says that awareness of symptoms and timely medical attention are important. Most outbreaks are localised because they are linked to specific contaminated water systems. Once the source is identified and controlled, the risk to the wider public generally decreases substantially.

Why Legionnaires’ disease is often underdiagnosed in India

Dr Reddy says, “Yes, Legionnaires’ disease is likely underdiagnosed in India. One major reason is that many cases present as community-acquired pneumonia and are treated empirically without specialised testing to identify the specific organism.”

Limited access to advanced laboratory diagnostics in many regions also contributes to underrecognition. Furthermore, Dr Hiremath mentions that routine surveillance for Legionella infections is not widespread, which means the true burden of disease may be higher than currently reported.