Pneumonia

Pneumonia is a condition that inflames the lung. It affects tiny air sacs called alveoli. People with pneumonia often have a cough, feel chest pain, have a fever, and may find it hard to breathe. How serious pneumonia is can differ for each person.

Most pneumonia happens because of infections from viruses or bacteria. Sometimes other microorganisms can cause it too. It is not always easy to know which germ causes it. Doctors look at symptoms, do a physical examination, and might use chest X-rays or blood tests. They may also look at sputum under a microscope to help figure out what is wrong.

Some health conditions can make pneumonia more likely. These include cystic fibrosis, chronic obstructive pulmonary disease (COPD), sickle cell disease, asthma, diabetes, or heart failure. Other risk factors are smoking, a weak ability to cough after an illness like a stroke, or a weakened immune system (immunodeficiency). Vaccines can help prevent some kinds of pneumonia, like those from Streptococcus pneumoniae bacteria, influenza viruses, or SARS-CoV-2. Good habits such as hand washing and treating respiratory symptoms quickly can also help prevent pneumonia. If bacteria cause pneumonia, doctors usually give antibiotics to treat it. In serious cases, people might need to stay in the hospital and could need oxygen therapy.

Signs and symptoms

People with pneumonia often have a cough with mucus, fever, trouble breathing, and chest pain when they breathe deeply. In children under five, common signs are fever, cough, and breathing that is fast or hard. Sometimes, more serious signs may show up, such as skin that looks blue or not wanting to drink.

Pneumonia from different germs can look a little different. For example, Legionella may cause stomach pain or diarrhea, while Streptococcus pneumoniae may cause coughing up colored mucus. Viral pneumonia often includes wheezing, whereas bacterial pneumonia does not usually include wheezing.

Cause

Pneumonia is usually caused by infections from bacteria, viruses, and sometimes fungi or parasites. Many different germs can cause it, but only a few are responsible for most cases. Sometimes, viruses and bacteria work together to make someone sick. In some cases, doctors cannot find the exact cause even after testing.

Bacteria like Streptococcus pneumoniae are a common cause, especially when people are out in the community. Other bacteria such as Haemophilus influenzae and Mycoplasma pneumoniae can also cause it. Viruses such as rhinoviruses, coronaviruses, and influenza are also common causes, especially in children and during flu season. Fungi usually cause pneumonia in people with weaker immune systems, while parasites are less common but can still affect the lungs.

Mechanisms

Pneumonia starts as an infection in the upper part of the respiratory system and spreads to the lungs. It causes lung inflammation. Normally, the upper airway helps protect us by fighting off harmful germs. In the lower airways, reflexes and special proteins help defend against infections. Sometimes, small amounts of contaminated secretions can get into the lower airways and cause pneumonia. How severe pneumonia becomes depends on the strength of the germ, how much is needed to cause infection, and how the body fights it back.

Bacteria usually enter the lungs when tiny amounts of germs from the throat or nose are aspirated, especially during sleep. Some bacteria, like Mycobacterium tuberculosis and Legionella pneumophila, can reach the lungs through contaminated air. Once in the lungs, bacteria can cause immune cells to release substances that lead to fever and other symptoms. These cells, along with fluid, fill the small air sacs in the lungs.

Viruses can reach the lungs through touching contaminated objects and then touching the face, or by inhaling infected droplets. Once inside, viruses can damage lung cells and cause inflammation. This can also make the body more vulnerable to bacterial infections, sometimes leading to bacterial pneumonia as well.

Diagnosis

Pneumonia is usually diagnosed using a chest X-ray and checking for physical signs. Lung ultrasonography can also help, especially when done by experts. In adults who look healthy and have normal lung exams, pneumonia is usually not the problem. Finding the exact cause can be tricky because there is no single test that can clearly tell if the infection is bacterial or not. A doctor’s judgment is often just as good as using special rules.

In children, doctors from the World Health Organization look for signs like coughing, trouble breathing, rapid breathing, or chest indrawing to diagnose pneumonia. For example, babies under two months should breathe fewer than 60 times a minute, while children aged one to five should breathe fewer than 40 times a minute to be considered okay. In children, low oxygen levels and chest indrawing are better signs than listening with a stethoscope. Other signs like grunting or flaring of the nose can also help in children under five.

For adults with mild cases, simple checks are often enough. If everything looks normal, pneumonia is very unlikely. A blood test called C-reactive protein (CRP) can help support the diagnosis. If CRP levels are low, antibiotics are usually not needed. Another test, procalcitonin, can help decide if antibiotics are needed — higher levels mean antibiotics are encouraged. For serious cases that need hospital care, doctors check oxygen levels, do chest X-rays, and run blood tests.

During a physical exam, doctors might notice a fast heart rate, low blood pressure, or low oxygen levels. They may also hear unusual sounds in the chest or notice that one side of the chest doesn’t expand normally. Chest X-rays are commonly used to see pneumonia, especially for serious cases or when the cause is unclear. Sometimes, a CT scan is used for more detailed images, but it involves more radiation and cost. Lung ultrasound can also help diagnose pneumonia without radiation but needs special skills to perform.

Prevention

Preventing pneumonia includes vaccination, making healthy choices, and treating other health problems. Vaccines help protect both children and adults from certain bacteria and viruses that cause pneumonia. For example, flu shots are recommended for everyone over six months old, and special vaccines for Streptococcus pneumoniae are important for young children and older adults.

Other ways to prevent pneumonia include stopping smoking, improving indoor air quality, and practicing good hygiene like washing hands and coughing into your sleeve. Taking care of underlying health issues, such as treating HIV or diabetes, can also lower the risk of pneumonia. For pregnant women, testing for certain infections and treating them if needed can help protect babies from pneumonia.

Management

Antibiotics taken by mouth, rest, simple analgesics, and fluids usually help people get better. For young children with mild pneumonia, antibiotics may help a little but often do not change how quickly they get better. People with other health problems, older adults, or trouble breathing may need more care. If symptoms get worse or do not improve, going to the hospital might be needed. Children who are struggling to breathe or have very low oxygen should go to the hospital.

For adults, a score called CURB-65 can help decide if someone needs to be in the hospital. A score of 0 or 1 usually means they can stay at home. A score of 2 might need a short hospital stay or close watching. Scores of 3–5 mean hospitalization is recommended. For bacterial pneumonia, antibiotics are important and should be started right away. The type of antibiotic depends on the person’s age, health, and where they got the infection. In the UK, amoxicillin is often used first, while in North America, amoxicillin, doxycycline, or a macrolide like azithromycin are common. For severe cases that need hospital care, certain antibiotics like cephazolin together with a macrolide are recommended.

For viral pneumonia caused by flu viruses, medicines like oseltamivir can help if started within 48 hours of symptoms. There are no special medicines for most other viral pneumonias. In cases of aspiration pneumonia, antibiotics are used based on where and how the infection started, with common choices including clindamycin or a mix of antibiotics.

Prognosis

With treatment, most types of bacterial pneumonia get better in about 3–6 days. Symptoms usually disappear after a few weeks. X-ray results normally go back to normal within four weeks. The chance of death is low.

Older people or those with existing lung problems may take longer to recover.

Complications can happen, especially in older people or those with other health issues. These may include conditions such as empyema, lung abscess, bronchiolitis obliterans, and severe breathing difficulties.

Clinical prediction rules like the CURB-65 score and the Pneumonia severity index help doctors decide if a person needs to be hospitalized.

In some cases, fluid can collect around the lung. If this fluid becomes infected, it is called an empyema and may need to be drained. Rarely, bacteria can form a lung abscess, which might require special treatment or drainage.

Pneumonia can sometimes cause serious breathing problems. It can also lead to other health issues, especially in people with weaker immune systems.

Main articles: Pleural effusion, Empyema, Parapneumonic effusion, Thoracentesis, Drainage catheter, Surgery, Radiologist, Hypoxemia, Hyposplenism, Myocardial infarction

Epidemiology

Main article: Epidemiology of pneumonia

Pneumonia is a very common illness that affects many people every year all around the world. It can be serious, especially for young children and older adults. In children under five years old, pneumonia can be a cause of illness, particularly in places with fewer medical resources.

In some years, many children around the world have had pneumonia. Most of these cases happen in countries with limited healthcare. Vaccines can help prevent pneumonia, and doctors often suggest hospital care for young children with pneumonia to make sure they get the right treatment.

History

Pneumonia has been known for thousands of years. Ancient doctors like Hippocrates wrote about its symptoms. Later, scientists learned about the bacteria that cause it. By the 1900s, new medicines and vaccines helped save many lives from pneumonia.

Society and culture

Each year on November 12, people around the world observe World Pneumonia Day to learn more about this illness and encourage help for those who are sick.

Pneumonia can cost a lot of money to treat. Countries spend billions of dollars each year to help people get better.