Parapneumonic effusion (PPE) is a type of pleural effusion. Pleural effusion is a buildup of fluid in the pleural cavity — the thin space between your lungs and chest cavity. There is always a small amount of fluid in this space. However, having too much fluid in the pleural space can prevent your lungs from fully expanding and make it hard to breathe.

The fluid buildup in PPE is caused by pneumonia.

PPE is a buildup of fluid in the pleural cavity. Empyema is a buildup of pus — a thick yellow-white liquid made up of bacteria and dead white blood cells. It’s also caused by pneumonia.

You can develop empyema if PPE isn’t treated quickly enough. Between 5 and 10 percent of people with PPE get empyema.

PPE is divided into three types based on the kind of fluid that’s in the pleural space and how it needs to be treated:

  • Uncomplicated parapneumonic effusions. The fluid may be cloudy or clear, and it doesn’t contain bacteria. PPE will get better when you take antibiotics to treat pneumonia.
  • Complicated parapneumonic effusions. Bacteria have traveled from the lungs into the pleural space, causing a buildup of fluid and white blood cells. The fluid is cloudy. It will need to be drained.
  • Empyema thoracis. Thick, whitish-yellow pus builds up in the pleural space. This can happen if pneumonia isn’t treated quickly enough.

Symptoms of PPE include:

  • fever
  • cough, sometimes with phlegm
  • fatigue
  • shortness of breath
  • chest pain

Because these are also symptoms of pneumonia, the doctor may need to do a chest X-ray or ultrasound to find out for sure if you have PPE.

PPE is caused by the lung infection, pneumonia. Both bacterial and viral pneumonia can cause PPE, but bacteria more often cause it.

When you have an infection, your immune system releases white blood cells to attack the virus or bacteria. White blood cells can damage the tiny blood vessels in the lungs, causing fluid to leak out of them and into the pleural space. If PPE isn’t treated, white blood cells and bacteria can collect in the fluid and cause empyema.

Between 20 and 57 percent of people who are hospitalized for pneumonia each year in the United States develop PPE. You’re more likely to get PPE if your pneumonia isn’t treated for several days.

Older adults and children are most vulnerable to getting PPE from pneumonia.

Treating bacterial pneumonia with antibiotics as soon as possible can prevent PPE and empyema.

If you don’t get better with antibiotics, or your PPE has progressed to empyema, then your doctor may need to drain fluid from the pleural space. One way to do this is with a procedure called thoracentesis. The doctor will insert a needle between two ribs on your side. Then, a syringe is used to remove fluid from the pleural space.

Another option is to place a hollow tube called a chest tube or a catheter in your chest to drain the fluid.

If draining the fluid doesn’t work, you may need surgery to remove it. Options include:

  • Thoracoscopy. The surgeon makes a few small incisions in your chest and inserts a small camera and instruments. This procedure can be used to both diagnose PPE and remove fluid from the pleural space.
  • Video-assisted thoracic surgery (VATS). The surgeon inserts a tiny camera and small instruments through a few small incisions in your chest wall. The surgeon is able to see an image of your lungs on a video screen to remove the fluid.
  • Thoracotomy. The surgeon makes an incision in the chest wall between your ribs and removes the fluid.

The outlook depends how severe your condition is, and how quickly you’re treated. Taking antibiotics as soon as possible can prevent pneumonia from turning into PPE and empyema. People with PPE typically have more severe or advanced pneumonia, which can be very serious and even life-threatening.

With treatment, the outlook is good. After you’ve been treated, your doctor will follow up with chest X-rays and other tests to make sure the infection has cleared and the fluid is gone.