What are the different types of pneumonia?

If you develop pneumonia at home, it's called community-acquired pneumonia (or CAP for short), even if you are admitted to the hospital during the course of the illness.

If you develop pneumonia while in a hospital, it is called hospital-acquired pneumonia (HAP for short) or nosocomial pneumonia. Pneumonia is considered to be hospital-acquired if it starts at least two days after you are admitted to the hospital, or within three months of leaving hospital.

This type of pneumonia (“hospital-acquired”) can also occur in a retirement home or nursing home, or at a medical facility such as a dialysis center.

Community-acquired bacterial pneumonia is usually caused by pneumococcal bacteria. Hospital-acquired pneumonia is often caused by staphylococcus bacteria, various intestinal (bowel) bacteria, or certain other bacteria such as Pseudomonas aeruginosa. Some of these bacteria might be multidrug-resistant, which means that certain antibiotics can't fight them. Because of this, hospital-acquired pneumonia usually needs to be treated with different types of antibiotics than community-acquired pneumonia does.

To be able to provide the right treatment, doctors also classify community-acquired pneumonia as mild, moderate or severe. They take the risk of complications into account here as well.

Pneumonia is considered to be mild if all of the following are true:

The patient

• is younger than 65 years old,
• is able to think and communicate clearly,
• has a normal blood pressure and pulse,
• isn't breathing too fast (less than 30 breaths per minute),
• has enough oxygen in their blood,
• hasn't used any antibiotics in the past three months,
• hasn't stayed in a hospital in the past three months, and
• doesn’t have any other serious medical conditions.

Then they aren't likely to have any complications. People with mild pneumonia can take antibiotics at home, in the form of tablets.

Pneumonia is considered to be moderate in people who have symptoms like drowsiness and confusion, low blood pressure, worsening shortness of breath, and risk factors such as other diseases and old age. These people need to have treatment at a hospital. Some are given a combination of two different antibiotics – at least at the beginning of the treatment.

Pneumonia is severe if vital organs or systems such as the heart, the kidneys or the blood circulatory system are at risk of failing, or if the lungs can no longer absorb enough oxygen. People then usually need treatment with antibiotics through a drip (infusion) in the intensive care unit of a hospital. Sometimes other treatments are needed too – for instance, with steroids or artificial respiration.

Pneumonia in children is only classified as either “not severe” or “severe.”

Experts also classify pneumonia based on factors other than how severe it is and where the patient picked up the infection. But that typically doesn't affect how the pneumonia is treated. Instead, it helps doctors to describe the disease better.

Typical pneumonia normally begins with a sudden high fever and chills, and then coughing with phlegm comes later.

Atypical pneumonia is caused by other, non-typical ("atypical") germs. Older people in particular have fewer or slightly different symptoms if they have atypical pneumonia: It then tends to start off rather slowly with a mild fever and/or headache and joint pain. Rather than coughing with phlegm, they're more likely to have a dry cough.

But atypical symptoms don't mean that the lung is less severely inflamed or that the course of the disease will be milder.

X-rays play an important role in distinguishing between these types: If an entire part of the lung (lobe) is visibly inflamed, it is known as lobar pneumonia. Depending on which lobe of the lung is affected, the pneumonia is referred to as upper, middle or lower lobe pneumonia.

If there are several areas of inflammation across different lung lobes, it is known as multilobar pneumonia. If the inflammation started in airway passages ( bronchi), it is called bronchopneumonia.

Sometimes it's the air sacs that are more inflamed (alveolar pneumonia), and sometimes it's the tissue between the air sacs (interstitial pneumonia).