From Keck Medicine of USC:

Pneumonia is a potentially serious condition: An estimated 1 million adults in the United States seek care in a hospital due to pneumonia every year, and 50,000 die from it.

“Pneumonia causes inflammation, fluid or pus to build up in the air sacs of the lungs, which are called alveoli,” explains Carrie Ward, MD, a primary carephysician at Keck Medicine of USC and a clinical assistant professor of medicine at the Keck School of Medicine of USC. “The alveoli are responsible for air exchange, and when they fill with fluid or are inflamed, they can’t effectively do their job, and the body receives less oxygen.”

Here’s what you need to know about pneumonia, including when to see a doctor.

1. Pneumonia can have different causes

Pneumonia is a lung infection most often caused by a virus or bacteria, and less often by fungi or chemical irritants, according to Ward. Pneumonia is usually contagious and can be spread through air droplets from coughing or sneezing, or from touch.

Bacterial pneumonia is often caused by Streptococcus pneumoniae, also called pneumococcal pneumonia. Other bacteria can lead to different types of pneumonia, such as Legionella pneumophila, which causes Legionnaires’ disease.

Viruses that cause pneumonia include influenza, the common cold (rhinovirus), respiratory syncytial virus (RSV) and COVID-19.

“COVID-19 pneumonia typically affects both lungs and is associated with a great deal of inflammation,” Ward points out. “This is why the infection can cause a significant cough and shortness of breath, and for some people, it can lead to the need for oxygen supplementation and even mechanical ventilation.”

Researchers are looking into how pneumonia from COVID-19 is different from pneumonia from other causes, why it causes significant long-term damage to the lungs and what kinds of new treatments might best target it.

2. You should call your doctor if you have these symptoms

It may be hard to tell if you have pneumonia just from how you feel, but there are things to look out for.

According to Ward, symptoms of pneumonia include:

• Cough, which can include mucus or phlegm
• Fever or chills
• Fatigue
• Shortness of breath
• Chest pain, especially when breathing or coughing

“To monitor your symptoms, I recommend keeping a working thermometer and a blood oxygen reader, called a pulse oximeter, at home,” she says.

If you have any of the following symptoms, Ward recommends seeking medical attention:

• A fever above 102°F, even after taking fever-lowering medications like acetaminophen or ibuprofen
• Blood oxygen level lower than 95%
• Coughing up blood — or sputum that contains blood

She adds that people whose immune systems are compromised (either by a medical condition or a medication) should contact their doctor if they think they are having pneumonia symptoms.

3. Pneumonia isn’t something you can diagnose yourself

Although you may suspect you have pneumonia based on your symptoms, only a doctor can tell for sure.

Ward says that pneumonia is diagnosed with a combination of the following:

• A physical exam, to listen for abnormal sounds in the lungs and to see how the patient is breathing
• Vital signs, to check temperature, heart and respiratory rate, blood pressure and oxygen saturation
• Blood tests, to check for signs of inflammation or blood infection
• Chest X-ray, to look for evidence of infection in the lung tissues

“Sometimes, special tests are utilized to examine respiratory secretions to help diagnose certain types of infectious pneumonia,” she adds.

4. Pneumonia can be serious — but not always

A case of pneumonia doesn’t necessarily require a hospital stay: If you are diagnosed with pneumonia but your symptoms aren’t severe, your doctor may direct you to manage it at home.

COVID-19 aside, bacterial pneumonia can be more serious than viral pneumonia — unless you have a case of pneumonia caused by the bacteria Mycoplasma pneumoniae, often referred to as walking pneumonia, the non-medical term for atypical pneumonia. Although it’s often mild, atypical pneumonia can still make you feel pretty bad and can also be spread to others.

5. Pneumonia treatment depends on the kind you have

How to fight pneumonia is based on the type you’re diagnosed with. For bacterial pneumonia, you’ll be given antibiotics to treat the infection. Unfortunately, treatment for viral pneumonia isn’t always so easy: You may be given antiviral medication, but you also might be instructed to ride out the virus at home. If this is the case, you may be told to take over-the-counter pain or fever medications, drink hot fluids and get plenty of rest.

If your pneumonia is severe and requires a hospital stay, you may get fluids (and antibiotics if necessary) through an IV and oxygen therapy to help you breathe. People with the most severe cases may be put on a ventilator. Most people will recover from pneumonia, although symptoms can linger for weeks.

6. You can reduce your chances of getting pneumonia

The measures you take for preventing other contagious diseases help prevent pneumonia as well.

“To protect yourself from pneumonia, including COVID-19 pneumonia, wear a mask, practice physical distancing and wash your hands or use hand sanitizer often,” Ward says.

Vaccines, like the flu vaccine, can help reduce your risk for getting infections that can lead to pneumonia; additionally, there’s a vaccine to prevent pneumococcal pneumonia for certain people.

“Remember to get your annual influenza vaccination, and if you are over 65 years old or are immunocompromised, get your pneumonia vaccinations,” Ward says. “When it is your turn for the COVID-19 vaccination, be sure to get that, too.”

Because smokers are at greater risk for pneumonia, if you are contemplating quitting smoking, your doctor can provide you with great resources to help you succeed and protect your lung health, she adds.