Pneumonia

Pneumonia is an inflammatory condition of the lung that mostly affects tiny air sacs called alveoli. People with pneumonia often have a cough that can produce mucus or be dry, feel chest pain, have a fever, and find it hard to breathe. The seriousness of pneumonia can vary a lot from person to person.

Most of the time, pneumonia happens because of infections caused by viruses or bacteria, and sometimes by other microorganisms. It isn’t always easy to find out which germ is to blame. Doctors usually figure out if someone has pneumonia by looking at their symptoms, doing a physical examination, and sometimes using chest X-rays, blood tests, or looking at sputum under a microscope to help confirm their diagnosis.

There are several things that can make a person more likely to get pneumonia, such as having health conditions like cystic fibrosis, chronic obstructive pulmonary disease (COPD), sickle cell disease, asthma, diabetes, or heart failure. Other risk factors include a history of smoking, having a weak ability to cough after an illness like a stroke, or having a weakened immune system (immunodeficiency). Vaccines are available to prevent certain kinds of pneumonia, such as those caused by Streptococcus pneumoniae bacteria, influenza viruses, or SARS-CoV-2. Good habits like hand washing and treating respiratory symptoms quickly can also help stop pneumonia. If a doctor thinks pneumonia is caused by bacteria, they will usually prescribe antibiotics to treat it. In serious cases, people may need to stay in the hospital and could benefit from oxygen therapy if their oxygen levels drop.

Signs and symptoms

People with infectious pneumonia often have a productive cough, fever, shortness of breath, and sharp chest pain during deep breaths. In children under five, common signs include fever, cough, and fast or difficult breathing. Sometimes, more severe signs may appear, such as blue-tinged skin or unwillingness to drink.

Pneumonia caused by different germs can have slightly different signs. For example, Legionella may cause abdominal pain or diarrhea, while Streptococcus pneumoniae may lead to rusty-colored sputum. Viral pneumonia often includes wheezing, whereas bacterial pneumonia does not as commonly.

Cause

Pneumonia happens mostly because of infections by bacteria, viruses, and sometimes fungi or parasites. Even though many types of germs can cause it, just a few are behind most cases. Sometimes, both viruses and bacteria can work together to cause the illness. In some cases, doctors can’t find the exact cause even after testing.

Bacteria like Streptococcus pneumoniae are a common cause, especially in community settings. Other bacteria such as Haemophilus influenzae and Mycoplasma pneumoniae can also be responsible. Viruses such as rhinoviruses, coronaviruses, and influenza also play a big role, 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 often begins as an infection in the upper respiratory tract that spreads to the lower respiratory tract. It is a type of lung inflammation. Normally, the upper airway helps protect us by competing with harmful germs for nutrients. In the lower airways, reflexes and special proteins help defend against infections. Small amounts of contaminated secretions can sometimes 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 combination of physical signs and a chest X-ray. Recently, lung ultrasonography has become more important because it can be more accurate than X-rays when done by experts. In adults who look healthy and have normal lung exams, pneumonia is usually not the problem. However, 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 to decide if someone has pneumonia.

In children, doctors from the World Health Organization define pneumonia based on signs like coughing, trouble breathing, rapid breathing, or chest indrawing. 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 for certain sounds. Other signs like grunting or flaring of the nose can also help in children under five.

For adults, simple checks are often enough if the case is mild. 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

Prevention of 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 by mouth, rest, simple analgesics, and fluids usually help people get better. For children aged 2 to 59 months with pneumonia that isn’t very serious, antibiotics may reduce the chance of treatment failure by 20%, but they don’t make a big difference in getting better or preventing the illness from coming back. However, people with other health problems, older adults, or those who are having a hard time breathing may need more advanced care. If symptoms get worse, don’t improve with home treatment, or complications happen, going to the hospital might be necessary. In children, those who are struggling to breathe or have very low oxygen levels should be taken to the hospital.

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

For viral pneumonia caused by flu viruses, medicines like oseltamivir can help if started within 48 hours of symptoms beginning. There are no specific 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 combination of antibiotics.

Prognosis

With treatment, most types of bacterial pneumonia improve within 3–6 days, and symptoms usually go away after a few weeks. X-ray results typically return to normal within four weeks, and the chance of death is low, less than 1%. However, older people or those with existing lung problems may take longer to recover.

Complications can occur, especially in older individuals 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 lead to serious breathing problems, making it hard to get enough oxygen. It can also cause sepsis, especially in people with weaker immune systems. Other serious conditions like heart attacks or blood clots should also be considered if symptoms are severe.

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 around 450 million people every year all around the world. It is especially serious for young children and older adults. In children under five years old, pneumonia is a leading cause of death, particularly in places with fewer medical resources.

In 2008, about 156 million children around the world had pneumonia. Most of these cases and deaths happen in countries with limited healthcare access. Vaccines can prevent many of these cases, and doctors often recommend hospital care for young children with pneumonia to ensure they get the right treatment.

History

Pneumonia has been known for thousands of years. Ancient doctors like Hippocrates described its symptoms, and later scientists discovered the bacteria that cause it. By the 1900s, new medicines and vaccines greatly reduced deaths from pneumonia.

Society and culture

Each year on November 12, people around the world observe World Pneumonia Day to raise awareness and encourage action against this illness.

Pneumonia causes significant economic burdens globally, with billions of dollars spent each year on treatment and care. In the United States alone, costs for treating pneumonia were very high, showing how much resources are needed to help people recover.