What is pneumonia, the lung infection that caused Diane Keaton’s death?

Beloved Oscar-winning actress Diane Keaton has died of pneumonia, according to a statement shared by her family with People magazine.

It was unclear whether she suffered from underlying health conditions that contributed to her death Saturday at age 79.

Here’s everything you need to know about the lung infection, what caused it, and how it led to Keaton’s death.

What is pneumonia?

Pneumonia is an infection that inflames the sacs in one or both lungs, according to the Mayo Clinic.

These air sacs fill with fluid or pus, causing a cough with phlegm or pus, fever, chills and difficulty breathing, depending on the clinic. The severity of the illness can range from mild to life-threatening, and it can lead to death in severe cases.

It is more serious for infants and people over 65 years old. People who have underlying health conditions or weakened immune systems are also at higher risk of severe pneumonia, the Mayo Clinic said.

What causes pneumonia?

Pneumonia can be caused by various pathogens, such as bacteria or viruses.

The immune system generally prevents these germs from causing infection in the lungs, but some can still evade the body’s defenses even if a person is healthy, according to the Mayo Clinic.

Dr. Ben Singer, a pulmonologist at Northwestern Medicine, said some types of pneumonia are caused by bacteria, but most often they are caused by a respiratory virus, such as the common cold, flu or Covid.

“Walking pneumonia” is caused by bacteria and is a milder form of the disease, according to the Mayo Clinic.

Patients may develop pneumonia during their hospital stay for other reasons, according to the Mayo Clinic. Hospital-acquired pneumonia can be more serious because the bacteria may be resistant to antibiotics and because patients may already have a weakened immune system.

People who use breathing machines are more vulnerable to pneumonia in the hospital, which is why many people who had early Covid variants died from pneumonia, Singer said.

It’s also possible to get aspiration pneumonia, which occurs when a person inhales food, drinks, vomit or saliva and is more likely in people whose gag reflexes are working abnormally, such as if they have a brain injury or swallowing problem or if they use drugs or alcohol, according to the Mayo Clinic.

What are the symptoms of pneumonia?

Symptoms can range from mild to severe.

In some cases, symptoms may be similar to colds and flu, but last longer and include:

• Chest pain when breathing or coughing.
• Confusion or changes in mental awareness (in elderly patients).
• Cough, which may produce phlegm.
• Fatigue.
• Fever, sweats, chills.
• Body temperature below normal (in elderly patients and those with weak immune systems).
• Nausea, vomiting, diarrhea.
• Shortness of breath.

Patients with pneumonia may face complications including sepsis or bacteria in the bloodstream, difficulty breathing, fluid around the lungs, and abscesses in the lungs.

Dr. Humberto Choi, a pulmonologist at the Cleveland Clinic, also noted that other complications can occur, such as pulmonary embolism, arrhythmias or even encephalopathy, which can affect the brain.

Those who have difficulty breathing, chest pain, a fever of 102 degrees Fahrenheit or a persistent cough should seek medical attention, according to the Mayo Clinic.

How does pneumonia cause death?

“It’s true that pneumonia tends to be more severe in people who are very, very young – so in infants – or in older adults, and that seems to be the age group that tends to have severe illness, but it can certainly affect anyone,” Singer said.

In Keaton’s case, even though she had no underlying illness, “that doesn’t mean that perfectly healthy people can’t get seriously ill, quickly with pneumonia,” Singer said.

Pneumonia is also a very common cause of sepsis, which is when “a serious infection creates an overwhelming response in the body to try to treat the infection,” Singer said. “The body tries to kill the infection, but as a result it harms the body itself.”

Both can also happen quickly. When the lungs malfunction, it causes a syndrome called acute respiratory distress syndrome, or ARDS, which affects the body very quickly, much like sepsis, which can progress within hours and become life-threatening.

Choi noted that low oxygen levels can progress from minutes to hours, and other complications, such as cardiac arrhythmia associated with pneumonia, can occur “very suddenly and out of nowhere.”

How is pneumonia prevented and treated?

Doing things like keeping good hygiene and maintaining a healthy immune system can help protect against pneumonia.

Vaccines to prevent certain types of pneumonia exist and are recommended for children ages 2 to 5, says the Mayo Clinic. In 2024, an independent group of CDC advisors voted 14-1 to lower the age for routine pneumococcal vaccinations to 50.

Doctors warn that vaccines only protect patients against certain types of pneumonia and not all.

For one thing, there are vaccines that protect against the viruses that cause pneumonia, like the flu, Covid and respiratory syncytial virus, or RSV, Singer said.

There is also a vaccine that targets a specific bacteria responsible for most cases of bacterial pneumonia, Singer said, but it is generally recommended for older adults and people with underlying illnesses. This vaccine is not given every year, but a doctor can advise whether a person needs a booster after receiving the first shot, he added.