Renowned Hollywood actress Diane Keaton has passed away following a struggle with pneumonia, her family revealed on Wednesday evening.

Insiders close to the Academy Award winner reported that her health began to sharply decline in the months leading up to her passing at the age of 79, which occurred this past Saturday.

Here’s an overview of the widespread yet potentially life-threatening illness that led to her demise.

What is pneumonia?

Pneumonia is a lung infection characterized by the inflammation of air sacs, which become filled with fluid or pus. This condition makes breathing difficult and can quickly lead to severe health complications.

Pneumonia is a prevalent ailment, impacting approximately 25 out of every 10,000 adults in the United States. The incidence rate rises notably with age, contributing to millions of cases each year.

What causes pneumonia?

Pneumonia can be caused by several organisms, but the biggest culprits are viruses and bacteria, according to the American Lung Association.

Viral pneumonia usually comes from bugs like the cold, flu, COVID-19 or RSV. Most cases are mild and clear up faster than bacterial pneumonia — but some can become severe.

Bacterial pneumonia can strike on its own or follow a viral infection, and it’s generally more common and serious than viral pneumonia. The leading cause is a bacteria called Streptococcus pneumoniae (pneumococcus), which normally lives in the upper respiratory tract.

While pneumonia itself isn’t contagious, the viruses and bacteria that cause it are. You can pick them up by touching infected surfaces or breathing in droplets from coughs and sneezes.

Fungus can also cause pneumonia, although it’s a much less common source. It’s usually acquired by inhaling fungal spores from the environment, rather than from contact with an infected person.

Who’s at risk?

Pneumonia can affect anyone, but the most vulnerable are kids under 2 and adults over 65 due to their weak or aging immune systems, according to the Mayo Clinic.

People with compromised immune systems — like those with HIV/AIDS, cancer patients on chemo or radiation or organ transplant recipients — also face a higher risk. The same goes for anyone recovering from a recent respiratory virus.

If you’re staying in the ICU or on a ventilator, your chances of being diagnosed increased.

Lifestyle habits can affect your chances, too. Smoking and heavy drinking make you more vulnerable, as does breathing in pollution or toxic fumes.

What are the symptoms?

Bacterial pneumonia can hit suddenly or creep in slowly. It can cause:

• High fever
• Fatigue
• Shortness of breath
• Rapid heartbeat
• Chills
• Chest or stomach pain
• Loss of appetite
• Cough that brings up yellow, green or bloody mucus .

Viral pneumonia usually develops over several days. It can cause:

• Fever
• Dry cough
• Headache
• Muscle aches
• Extreme fatigue

Babies and young children may not show typical signs. Instead, look for trouble feeding, nonstop crying, limpness, pale skin, noisy breathing, vomiting, fussiness or coughing.

Is pneumonia deadly?

It’s the top reason that US children end up in the hospital, and for adults, its the second leading cause of hospital stays — trailing only behind childbirth, according to the American Thoracic Society.

Some cases are mild, but pneumonia can be brutal. Recovery can take weeks, and complications like respiratory failure, fluid buildup, lung abscesses and bloodstream infections can turn deadly.

Every year, about 1 million adults in the US land in the hospital with pneumonia — and roughly 50,000 don’t survive.

Can you prevent it?

Vaccines are one of the best defenses against pneumonia. Shots targeting the bacteria and viruses that cause the infection can lower your risk of getting it, and if you do get sick, they can help keep it from turning severe.

Beyond vaccines, simple healthy habits help, including quitting smoking, cutting back on booze, eating right, exercising and getting plenty of rest.

Treat any other infections or health issues that could weaken your immune system is also a crucial part of staying ahead of pneumonia.