Legionnaires' Disease: Can Air Conditioning Make You Sick?

A recent Legionnaires' disease outbreak on Manhattan's Upper East Side has put health officials on high alert after more than 20 people became infected and several required hospitalization. Investigators traced the outbreak to contaminated cooling towers on large buildings, raising an important question: Could the air conditioning around us be making us sick?

That is both reassuring and cautionary. It is rarely your home air conditioner. The real danger is in large water-cooling systems that are poorly maintained and can harbor a potentially deadly bacterium called Legionella.

What Is Legionnaires' Disease?

Legionnaires' disease is a severe form of bacterial pneumonia caused by Legionella pneumophila. This bacterium naturally lives in lakes, rivers, and other freshwater environments, where it usually poses little risk. Problems arise when it enters man-made water systems and multiplies in warm, stagnant water.

Typical sources include:

1. Office buildings, shopping centers, and cooling towers.
2. Air conditioning equipment (central).
3. Ornamental fountains.
4. Spas and hot tubs.
5. Plumbing in hotels and hospitals.
6. Large water tanks.

The bacteria spread when contaminated water is broken into tiny droplets that become airborne. Breathing in these microscopic droplets allows the bacteria to reach the lungs and cause infection.

Can You Catch It From Someone Else?

The good news is that Legionnaires’ disease is not thought to be contagious. It is not usually transmitted from person to person, unlike flu or COVID-19. The infection is acquired almost exclusively by inhalation of contaminated water droplets.

Who Is Most at Risk?

Although anyone can develop Legionnaires' disease, some people are much more vulnerable to severe illness. The risk is highest in individuals who:

• Are older than 50 years.
• Smoke or have smoked in the past.
• Have chronic lung disease.
• Have diabetes or kidney disease.
• Have weakened immune systems.
• Take medications that suppress immunity.

Healthy younger adults can also become infected, but they are generally less likely to develop severe complications.

Which Symptoms You Should Never Ignore

Symptoms generally appear 2 to 10 days after exposure and can resemble severe pneumonia. Look out for:

• High fever with chills.
• Continuous cough.
• Breathlessness.
• Heart pain.
• Muscle aches.
• Fatigue.
• Headache.

Some people may also experience diarrhea, nausea, vomiting, or confusion, particularly older adults.

Because these symptoms overlap with many respiratory illnesses, laboratory testing is usually needed to confirm the diagnosis.

Is It Treatable?

Yes. Legionnaires' disease responds well to appropriate antibiotics, especially when treatment begins early.

However, many patients require hospitalization, and severe cases may need oxygen therapy or intensive care. Delayed treatment increases the risk of serious complications, making early medical evaluation essential.

Can It Be Prevented?

The most effective prevention does not happen at home; it happens behind the scenes.

Building owners and facility managers should:

• Clean and disinfect cooling towers regularly.
• Prevent water from becoming stagnant.
• Monitor water temperatures.
• Maintain plumbing systems properly.
• Test for Legionella when appropriate.

There is currently no vaccine against Legionnaires' disease.

For the public, prevention mainly involves awareness. If a Legionnaires' outbreak has been reported in your area and you develop pneumonia-like symptoms, seek medical attention promptly.

When Should You See a Doctor?

Do not ignore symptoms if you experience:

• A persistent high fever
• Difficulty breathing
• Chest pain
• A severe or worsening cough
• Confusion or unusual drowsiness

This is especially important if you are over 50 or have chronic medical conditions.

Legionnaires’ disease is uncommon, but outbreaks serve as a reminder that building water systems require regular maintenance to keep the public safe. Your home air conditioner is unlikely to be spreading the bacteria, but contaminated cooling towers, plumbing systems and other large water installations can be sources if not well maintained.

The good news is that Legionnaires’ disease is both preventable and treatable. Knowing the symptoms, who’s most at risk, and seeking medical care early can make all the difference. Recent events have demonstrated that one of the best ways to protect yourself and those you love is to be informed.