What is Pneumonia?

What is Pneumonia?

Pneumonia is an infection in the lungs caused by bacteria, viruses, or fungi. Pneumonia can affect one or both lungs, and the symptoms include cough, fever, trouble breathing, and fatigue. Symptoms can be mild and go away without treatment, but sometimes they are severe and may require hospitalization.

Anyone can get pneumonia, but children younger than two years, adults 65 and older, and people with conditions that weaken their immune systems are at a higher risk of getting infected. Vaccines for certain types of pneumonia are available and are recommended for those at high risk.

Types of Pneumonia


The types of pneumonia are classified according to the cause of the disease and include:

  • Bacterial pneumonia is caused by a bacterial infection from certain types of bacteria and can develop on its own or following a viral infection such as a cold or the flu. Bacteria that can cause pneumonia include:
    • Streptococcus pneumoniae
    • Legionella pneumophila
    • Mycoplasma pneumonia
  • Viral pneumonia can be mild and may go away without treatment, but sometimes can require treatment. People who have viral pneumonia are at risk of also getting bacterial pneumonia.
  • Fungal pneumonia is a less common type of pneumonia and may infect people who have chronic health problems or weakened immune systems.
  • Walking pneumonia is a non-medical term that describes a mild case of pneumonia. Some doctors may call it “atypical pneumonia”.

Stages of Pneumonia


Bacterial pneumonia, the most common type of pneumonia, has four stages. The four stages are:

  • Stage 1 congestion. In the first 24 hours of infection, only some bacteria and white blood cells to fight infection are present. The lungs may have increased blood flow and swelling to the airways. Early symptoms are coughing and fatigue.
  • Stage 2 red hepatization. Bacteria multiply white and red blood cells in the airways and air-sacs (alveoli) give the lungs a red appearance. Symptoms may get worse than before.
  • Stage 3 gray hepatization. Damaged red blood cells in the lungs give the lungs a gray color. Symptoms continue to be present.
  • Stage 4 resolution. Inflammatory fluids and damaged cells in the lungs start to disappear and normal airways and air-sacs are returning to their normal state. Pneumonia symptoms improve and patients begin to feel better.

Signs & Symptoms of Pneumonia


Symptoms of pneumonia can be mild or more serious. Some people feel better, and their milder symptoms go away after one to two weeks. Most people, though, experience symptoms for a month or longer before they can return to their usual routine.

A primary care doctor can help by providing treatment if symptoms persist so that patients may return to their normal activities faster.

Pneumonia symptoms include:

  • Cough, often with phlegm
  • Fever
  • Shortness of breath
  • Chills
  • Sweating
  • Fatigue
  • Chest pain
  • Loss of appetite
  • Blueness of the lips and nailbeds

The symptoms can be different for people of different ages:

  • Newborns, infants, and children under the age of 5, may sometimes have no symptoms, but some may have:
    • High fever
    • Cough
    • Fast breathing or wheezing
    • Vomit
    • Fatigue
    • Restlessness
  • Older adults and people with severe illnesses or weak immune systems may have other symptoms, including:
    • Low body temperature (lower than normal)
    • Confusion or sudden changes in mental alertness

What Causes Pneumonia?


Bacterial, viral, and fungal infections can cause pneumonia. Bacteria are the most common cause of pneumonia.

  • Bacterial pneumonia is caused by certain types of bacteria and can develop on its own or following a viral infection such as a cold or the flu. Bacterial pneumonia can affect people of all ages, but young children and older adults are at a higher risk as well as people with a weakened immune system. Bacteria that cause pneumonia include:
    • Streptococcus pneumoniae
    • Legionella pneumophila
    • Mycoplasma pneumoniae
    • Chlamydia pneumoniae
    • Haemophilus influenzae
  • Viral pneumonia can be mild and may go away on its own but sometimes can require treatment. People who have viral pneumonia are at risk of also getting bacterial pneumonia. Viruses that cause pneumonia include:
    • Respiratory syncytial virus (RSV)
    • Viruses that cause the common cold and flu (influenza)
    • SARS-CoV-2, the virus that causes COVID-19
  • Fungal pneumonia is a less common type and may infect people with chronic health problems or weakened immune systems. Some of the types include:
    • Pneumocystis pneumonia (PCP)
    • Coccidioidomycosis
    • Cryptococcus
    • Histoplasmosis

Risk Factors for Pneumonia

Risk Factors

Anyone can get pneumonia>, but certain factors increase the risk of developing pneumonia including:

  • Age including children aged 2 and younger, and adults over the age of 65, are at higher risk.
  • Medical conditions for people with certain medical conditions are at higher risk, such as:
    • Lung disease
    • Weakened immune system
    • Flu or the common cold (people who have recently been sick are at higher risk of contracting pneumonia)
  • Smoking and other habits such as heavy alcohol use.
  • Living environment or being in close contact with other people who may have been exposed to pneumonia can increase the risk of being infected even when efforts to prevent such infections are put in place. These may include:
    • Hospitals
    • Long-term care facilities



Complications associated with pneumonia include:

  • Lung abscesses. Pockets of pus that form inside or around the lung.
  • Respiratory failure. A condition that can cause shortness of breath or a feeling of not having enough air and may require the use of a breathing machine or ventilator.
  • Pleural effusion. Water on the lungs, accumulation of fluid between the layers of the pleura, the thin membranes that line the lungs, and the inside of the chest cavity.
  • Sepsis. A condition that happens when the infection spreads to the bloodstream and may lead to organ failure.

How to Prevent Pneumonia


Vaccines can prevent certain types of pneumonia. They may also promote a healthy lifestyle may help prevent pneumonia, including:

  • Flu vaccine. A yearly vaccine can prevent the flu, increasing the risk of contracting bacterial pneumonia.
  • Pneumonia vaccine. Two types of pneumonia vaccines can help prevent pneumonia caused by bacteria -- pneumococcal conjugate vaccines (PCVs) and pneumococcal polysaccharide vaccines (PPSV23). The type of vaccine recommended is based on age and medical condition. In certain conditions, your doctor may recommend both types of vaccine.
  • Good hygiene including:
    • Washing hands well and often
    • Avoiding close contact with people who are sick
    • Staying home when sick to avoid infecting others
    • Cleaning and disinfecting surfaces that many people touch
  • Not smoking and avoiding excessive alcohol drinking.
  • Healthy lifestyle to maintain good health generally.
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Trust NewYork-Presbyterian for Pneumonia Care

At NewYork-Presbyterian, we are experienced in caring for a diverse population of patients. We offer services for adults, children, adolescents, and older patients of all backgrounds. Our primary care services of family medicine doctors, internists, and pediatricians are available at more than 15 practices throughout Manhattan. Same-day appointments can be made for urgent needs. Scheduling is easy, we offer early, late, and weekend hours, and we accept most insurance plans. Learn more about our primary care locations and or schedule a virtual visit.