Two people have died among 58 cases of Legionnaires’ disease in a cluster that broke out in the central Harlem area of New York City, officials said Monday.

The big picture: People living and working in the area, which spans five zip codes, who are experiencing flu-like symptoms or having difficulty breathing should immediately contact a health care provider, the city’s health department urged.

• Last week, the New York City Health Department said that one person had died and 22 had been diagnosed in the cluster since July 25. Now, that number has more than doubled.

Read more about the cluster and the disease:

What are officials saying about Legionnaires’ cases?

What they’re saying: Acting New York City Health Commissioner Michelle Morse noted that while the disease can be effectively treated if caught early, high-risk New Yorkers — including people over 50, smokers or individuals with chronic lung conditions — “should be especially mindful of their symptoms and seek care as soon as symptoms begin.”

• City officials emphasized in a notice that the issue is not related to any building’s plumbing system and that it is safe to drink water, bathe, cook and use air conditioning.

What’s causing the spread?

City officials believe the likely source of the bacteria causing people to fall ill was cooling towers in the central Harlem area, which spray mist.

• They said “remediation required by the Department has been completed for the 11 cooling towers with initial positive screening results” for a form of bacteria that causes Legionnaires’ disease.

What is Legionnaires’ disease?

Legionnaires’ disease is a serious form of pneumonia caused by Legionella bacteria, according to the Centers for Disease Control and Prevention.

• Legionella, which grow in warm water, are usually harmless and found naturally, per the Occupational Safety and Health Administration, but can become a potentially deadly health hazard when the bacteria grows in places like cooling towers or HVAC systems.
• Outbreaks have also been linked to hot tubs, fountains and swimming and birthing pools, according to the Mayo Clinic.

By the numbers: In general, reported cases of Legionnaires’ increased in the years since the early 2000s, per the CDC.

• Around 6,000 cases of the disease are reported each year, but scientists believe reported totals are far lower than the actual number due to difficulty distinguishing from other types of pneumonia.
• According to the New York State Department of Health, between 200 and 800 cases are reported every year in the state — though most occur as single, isolated events.

Is Legionnaires’ disease contagious?

In general, people do not spread Legionnaires’ disease to other people, according to the CDC.

• When Legionella grows, it can spread via droplets of water small enough for people to breathe in.
• Though it’s less common, people can also get sick if drinking water containing the bacteria accidentally goes into the lungs (think, if the water goes “down the wrong pipe.”)

What are the symptoms of Legionnaires’ disease?

Symptoms of Legionnaires’ typically develop within two days to two weeks after exposure to Legionella, per the CDC, but it can take even longer.

• The symptoms of the disease include coughing, a fever, muscle aches, headaches and shortness of breath.
• Some people can also develop gastrointestinal symptoms.

Threat level: Most healthy people exposed to Legionella don’t get sick, but some people are at high risk.

• Those groups at increased risk include current or former smokers, people 50 years or older, people with chronic lung disease and people who have a condition or take medication that weakens their immune system.

Yes, but: Untreated Legionnaires’ can kill, the Mayo Clinic says, and according to the World Health Organization, it usually worsens during the first week.

• Diagnosing and treatment the disease as soon as possible can cut down on the time it takes to recover and prevent complications, like lung failure.

How is it treated?

It requires treatment with antibiotics, and in most cases, can be treated successfully.

• While healthy people usually do recover, they often still need care in a hospital, according to the CDC.

There is no vaccine to prevent the disease, per the American Lung Association.

• Rather, the best way to prevent people from getting sick is for businesses and residential owners to ensure buildings’ water systems are well-maintained.
• The organization also advises avoiding exposure to decorative fountains, hot tubs and other water sources until one knows how well they’re maintained.
• To prevent the growth of Legionella in household water systems, New York state officials recommend letting faucets run on low before use. They also advise draining garden hoses, regularly checking chlorine levels in pools and hot tubs and flushing hot water heaters twice a year.

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