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  • An infection that inflames air sacs, which may fill with fluid, in the lungs
  • Symptoms include a cough with colored mucus, fever, confusion, trouble breathing, and fatigue
  • Treatment involves antibiotics or getting rest to help the infection go away on its own
  • Involves Pulmonary, Critical Care & Sleep Medicine and Internal Medicine



Whether it’s bacterial, viral—or the friendlier sounding “walking” pneumonia—chances are you or someone you know has had this illness at some point. The infection, which is caused by bacteria, viruses or fungi, can occur in one or both of the lungs. It can be mild or life-threatening, especially to the elderly, the very young or those with compromised immune systems.

There are more than 30 different microorganisms (or microbes) that can cause pneumonia, and identifying the correct one isn’t always easy. At Yale Medicine, our physicians are experienced and skilled at treating everything from the most basic form of pneumonia to the more serious cases that might require hospitalization.

Researchers at Yale School of Medicine are studying how to better identify different types of pneumonia strains, so that the antibiotics given to patients are the best possible fit. “There has been a big push regarding antibiotics stewardship—how to treat patients appropriately with antibiotics, who needs antibiotics, and also what are some of the non-antibiotic alternatives to treat patients,” says Charles Dela Cruz, MD, a pulmonologist at Yale Medicine. 

What is pneumonia?

Pneumonia is an infection in which the air sacs in one or both of the lungs are filled with fluid or pus and become inflamed. The inflammation causes cough with phlegm, along with fever, chills and breathing troubles.

Pneumonia is often classified by where it was acquired. Hospital-acquired pneumonia, picked up during a hospital stay, is often more severe for two reasons. One, because the bacteria may be resistant to antibiotics and, two, the people who get it are already sick. Community-acquired pneumonia means it was acquired outside of a medical setting.

What causes pneumonia?

Pneumonia is caused by bacteria, viruses or fungus. There are literally dozens of different causes of pneumonia, grouped by the most common types. These are:

  • Bacterial pneumonia. This is caused by bacteria, the most common of which is streptococcus pneumoniae. The pneumonia might just affect one small area of your lung, or it may encompass all of both of your lungs.
  • Viral pneumonia. Responsible for about one-third of all pneumonia cases, this type is caused by various viruses, including flu (influenza). People may be more likely to get bacterial pneumonia if they first have viral pneumonia. Viral pneumonia is usually not as serious as bacterial and typically goes away more quickly.
  • Mycoplasma pneumonia. Also known as walking pneumonia, this type is considered atypical because its symptoms and physical signs may vary. Also, it causes a milder illness. It most often occurs in older children and young adults.
  • Fungal pneumonia. Fungi from soil or bird droppings can cause pneumonia in people who inhale large amounts of these organisms. One type, pneumocystis jirovecii pneumonia (PCP), generally affects people with weak immune systems, including those with AIDS.

Who is at risk for pneumonia?

Pneumonia strikes all ages, but it can be the most serious for certain populations, including: 

  • Infants
  • Children younger than 2
  • Adults over age 65
  • People with certain medical conditions, including heart failure or chronic lung problems
  • People who smoke

What are the symptoms of pneumonia?

Symptoms of pneumonia, no matter the type, include: 

  • Cough that may produce green, yellow or bloody mucus
  • Fever (can be as high as 105 for bacterial pneumonia)
  • Bluish color to lips and fingernails
  • Confused state or delirium (in adults over age 65)
  • Heavy sweating
  • Rapid or troubled breathing
  • Extreme fatigue
  • Rapid pulse
  • Sharp or stabbing chest pain when breathing or coughing

Symptoms that signal the need to see a doctor include trouble breathing, chest pain, a persistent fever of 102 degrees or higher, or a persistent cough. It’s especially important for people who fall into the higher risk groups to see a doctor.

How is walking pneumonia different?

Walking pneumonia, also known as atypical pneumonia, is caused by mycoplasma pneumoniae bacteria. It usually causes cold-like symptoms, in addition to a fever (often low grade) and a hacking cough. It is most common in school-aged children and young adults, says Annette Cameron, MD, a Yale Medicine pediatrician.  

Because this type of pneumonia typically causes milder symptoms, it may go undiagnosed for a while, especially if the child is able to participate in normal activities and isn’t as visibly sick as he or she would be with other forms of pneumonia. “And that’s why it’s called walking pneumonia,” Dr. Cameron says. “It might just be a little bit of malaise. Sometimes you can have community-acquired, or bacterial pneumonia, along with walking pneumonia, in which case we would just treat both of them.” 

How is pneumonia diagnosed?

A physician will first ask about your medical history and take a physical exam. This includes listening to your lungs with a stethoscope. The doctor does this to check for what is called “rales,” which are small clicking, bubbling or rattling sounds in the lungs.

“Rales, or crackling, is the classic sound when it comes to pneumonia, and when you are hearing it in a specific area of the lungs, then it is likely to be bacterial pneumonia,” Dr. Cameron says. “You don’t always need to get a chest X-ray if you hear the crackling, if there are other symptoms like a persistent cough, fever and a change in respiratory rate, which might be a little bit quicker.”   

Doctors also measure oxygen saturation (through a pulse oximeter, a small sensor clipped to a finger). 

“This can be a really subtle clue. Often times you can have a normal exam, especially with a little child who doesn’t know how to take deep breaths,” Dr. Cameron says. “But if the O2 saturation is a little off, maybe even 94 when we really want 97 or above, and the child is coughing a lot, we might want to do a chest X-ray to be sure. There is no strict formula. A lot of it depends on gut, or experience, in fitting the story together.”

Other tests, if needed, include:

  • Blood tests. This will show whether infection is present and possibly identify the organism causing it. But precise identification isn’t always possible.
  • Sputum test. A sample of fluid from your lungs (sputum) is taken after it coughed up. It then gets analyzed to see if there’s a lung infection. 

How is pneumonia treated?

Pneumonia treatment depends on numerous factors, including what type you have and how severe it is. Usually, it can be treated at home, but in serious cases, it may require a hospital stay.

“If the pneumonia is bacterial, it will respond to antibiotics and we typically start with amoxicillin,” Dr. Cameron says. “If it’s viral, antibiotics won’t help, but they might help walking pneumonia, in which case we would use azithromycin.”

If your pneumonia is bacterial and it is unknown which bacterium is causing the infection, your doctor will choose among various antibiotics for treatment. Fever and pain reducers, such as Tylenol or Motrin, will help with discomfort.

For viral pneumonia, getting plenty of rest and staying hydrated should be enough. The infection should go away on its own. 

What about the influenza and pneumococcal vaccines?

Because the flu is a common cause of pneumonia, consider getting your flu vaccine. “This is one of the reasons we recommend the flu vaccine, because not only can you get the flu virus and feel really miserable, but you can end up with a secondary bacterial infection which could be very serious or even fatal,” Dr. Cameron says.

There is also a pneumococcal vaccine, which offers protection from a common form of bacterial pneumonia. The shot is recommended for children younger than 5 and adults 65 and older. It is also advised for children and adults who are at an increased risk of pneumonia due to other health conditions. 

What stands out about Yale Medicine’s approach to pneumonia?

Pneumonia is a common infection in both children and adults and can often be easily treated. However, if specialized care is required, Yale Medicine physicians practice at both Yale New Haven Hospital and Yale New Haven Children’s Hospital.

Furthermore, our researchers are involved in developing ways to more quickly and accurately diagnose lung infections through the Yale Center for Pulmonary Infection Research and Treatment (CPIRT). “We don’t tend to think of pneumonia as a chronic condition. But some  patients end up with longer-term problems,” says Dr. Dela Cruz, director of the CPIRT. The center focuses on finding new potential treatment options and running clinical trials to better understand the disease.