Pneumonia: Infection in the Lungs

Pneumonia is inflammation of the lung tissue, usually caused by infection. It affects the tiny air sacs where oxygen normally moves into the blood. Pneumonia ranges from an illness managed at home to severe disease requiring hospital and respiratory support.

What pneumonia is Pneumonia is inflammation of the lung tissue, usually caused by an infection. It mainly affects the tiny air sacs called alveoli and the surrounding tissue. Healthy alveoli fill with air when you breathe. Oxygen crosses their thin walls into nearby blood vessels, while carbon dioxide moves in the opposite direction. During pneumonia, affected air sacs become inflamed and may fill with fluid, inflammatory cells and secretions. This leaves less space for air and makes gas exchange less effective. Pneumonia may affect one limited area, several patches or large parts of one or both lungs. The amount of lung involved does not by itself determine how unwell someone becomes. Age, other illnesses, oxygen levels and the body's response also matter. Pneumonia is not every chest infection A chest infection is a broad term covering infections in different parts of the respiratory system. Bronchitis mainly affects the larger airways. Bronchiolitis affects smaller airways, particularly in babies. Pneumonia affects the deeper gas exchanging lung tissue. Symptoms can overlap, so cough, fever, coloured phlegm or chest discomfort cannot identify pneumonia by themselves. Pneumonia may begin suddenly or develop gradually over several days. The illness can be mild, moderate or severe. A person may also deteriorate after initially appearing to have a less serious respiratory infection. What causes pneumonia Bacteria and viruses are common causes. Influenza, respiratory syncytial virus and COVID 19 can cause viral pneumonia or be followed by bacterial pneumonia. Fungi can also cause pneumonia, but fungal pneumonia is uncommon in otherwise healthy people in the UK. It is more relevant when immune defence is significantly weakened or after particular environmental exposures. Clinicians cannot always identify the exact organism. Different microorganisms can produce similar symptoms, examination findings and chest X ray appearances. A person may also have more than one infection at the same time. Antibiotics act against bacteria, not viruses. However, NICE recommends antibiotics after a clinical diagnosis of community acquired pneumonia because bacterial infection may be present and cannot always be reliably excluded at the first assessment. Community acquired and hospital acquired pneumonia Community acquired pneumonia begins outside hospital or very soon after admission. It includes pneumonia developing in someone living in a care or nursing home. Hospital acquired pneumonia develops after a person has spent time in hospital and was not already incubating the infection on admission. Recent hospital care, previous antibiotics and local resistance patterns can affect which bacteria are likely. These labels describe where the infection was acquired. They help clinicians choose investigations and antimicrobial treatment. They do not state how severe the illness will be. Aspiration pneumonia Aspiration means material enters the airway instead of travelling down the oesophagus towards the stomach. Small amounts of saliva are sometimes inhaled without causing disease. Aspiration pneumonia develops when enough bacteria rich material from the mouth, throat or digestive tract reaches the lungs and causes inflammation and infection. Risk is higher when swallowing or consciousness is impaired. Possible contributing conditions include stroke, neurological disease, reduced alertness, swallowing difficulty and recurrent vomiting. Poor oral health can increase the number of harmful bacteria in material that is aspirated. Aspiration pneumonia is not the same as chemical pneumonitis. Chemical pneumonitis is sudden lung inflammation caused by inhaling an irritating substance, such as acidic stomach contents. Infection may not be present initially, although the two conditions can overlap. Who is more vulnerable to serious pneumonia Anyone can develop pneumonia. Babies, young children and older adults are more likely to become seriously unwell. Risk is also higher with long term heart or lung disease, frailty or significantly weakened immune defence. Recent hospital admission, surgery or invasive respiratory support can increase exposure to hospital associated organisms. Smoking damages airway defences and increases the risk of respiratory infection. Swallowing problems and reduced consciousness increase the risk of aspiration pneumonia. Risk factors do not diagnose pneumonia or predict the outcome with certainty. A previously healthy person can still develop severe disease, while many higher risk people recover fully. How pneumonia may present Common features include cough, breathlessness, fever, chest pain, tiredness and reduced appetite. A cough may be dry or produce phlegm. Chest pain caused by irritation of the lung covering may feel sharp and worsen during a deep breath or cough. This is called pleuritic pain. Older people may become newly confused or less able to manage normal activities. Babies may breathe rapidly, grunt, feed poorly or become unusually sleepy. The pattern varies with age, cause and severity. Not every person has every feature. Symptoms such as cough, fever and breathlessness also occur with many conditions other than pneumonia. How clinicians assess possible pneumonia In the community, a clinician can make a clinical diagnosis from the symptoms, examination and observations when pneumonia appears likely. A chest X ray is not required before every community diagnosis. The clinician checks breathing rate, oxygen saturation, pulse, blood pressure, temperature and alertness. They listen for abnormal breath sounds and examine for other possible causes of the illness. Low oxygen saturation may suggest impaired gas exchange. However, pulse oximeters have limitations and may be less accurate in some circumstances, including on pigmented skin. The number must be interpreted alongside the person's appearance, breathing effort and usual oxygen level. Adults presenting to hospital with suspected pneumonia usually have chest imaging to confirm the diagnosis. A chest X ray may show areas where air filled lung has become denser because of inflammation and fluid. This appearance is sometimes called consolidation. Lung ultrasound can sometimes support rapid diagnosis or examine complications involving the pleura. Imaging does not always identify the organism and may not distinguish every possible cause. Blood tests can assess inflammation, kidney function, liver function and other effects of severe illness. Microbiological tests may include sputum samples, respiratory swabs, blood cultures or urinary antigen tests. Not everyone needs every test. NICE advises against routine microbiological testing in adults with low severity community acquired pneumonia and children with non severe disease. Testing becomes more relevant with severe illness, suspected sepsis, treatment failure or hospital acquired infection. How severity is judged Severity is not determined by one symptom or one X ray feature. Clinicians consider breathing effort, oxygen level, circulation, alertness, age, other illnesses, complications and the speed of deterioration. For adults with community acquired pneumonia, clinicians may use CRB65 in primary care and CURB65 in hospital. These tools consider features associated with a higher risk of death, including confusion, fast breathing, low blood pressure and older age. CURB65 also includes a blood urea measurement. The scores support professional judgement rather than replacing it. Someone with a low score may still need hospital care because of low oxygen, significant comorbidity, pregnancy, frailty or a pleural complication. Severity in babies, children and young people is assessed mainly through clinical judgement. Concerning features include marked breathing difficulty, low oxygen saturation, grunting, severe chest indrawing, inability to drink or breastfeed, lethargy and reduced consciousness. These professional assessments are not home scoring systems. A person who is deteriorating or struggling to breathe needs medical help rather than an attempted self calculation. Treatment principles Treatment depends on severity, likely cause, recent healthcare exposure, other illnesses and the person's ability to take oral medicines. NICE recommends antibiotics for people diagnosed with community acquired pneumonia. Oral antibiotics are generally preferred when the person can take them and does not need intravenous treatment. More severe pneumonia may require hospital care, intravenous antibiotics, oxygen, carefully assessed fluids and close monitoring. Respiratory support may be required if standard oxygen does not maintain an appropriate level. Some adults admitted with high severity community acquired pneumonia may be offered a corticosteroid alongside antibiotics. This is a selected hospital treatment rather than routine treatment for everyone with pneumonia. When microbiological results become available, clinicians review the antimicrobial choice. They may change to a narrower spectrum antibiotic when this will treat the identified organism safely. If pneumonia has led to sepsis, respiratory failure or another serious complication, treatment follows the relevant emergency pathway. An accumulation of fluid or infection around the lung may require specialist assessment and sometimes drainage. Expected recovery Recovery speed varies. Most people improve, but cough, breathlessness and fatigue may continue after the infection has started resolving. For most adults receiving treatment, fever should resolve within about one week. Chest pain and sputum usually reduce substantially within four weeks, while cough and breathlessness may take about six weeks. Most symptoms have usually resolved by three months, although fatigue may remain. Some people take up to six months to feel back to normal, particularly after severe pneumonia. For most children, fever and breathing difficulty should resolve within three to four days after treatment starts. A cough may continue for up to four weeks if the child is otherwise recovering well. These are expected patterns, not deadlines. Symptoms that worsen rapidly, fail to begin improving within three days or are accompanied by increasing systemic illness require reassessment. Reducing future risk Vaccination can reduce the risk of infections that may cause pneumonia. Relevant programmes include pneumococcal, influenza, COVID 19 and respiratory syncytial virus immunisation for eligible groups. Vaccines do not prevent every case because pneumonia has many causes. Eligibility and schedules change, so current NHS advice should be followed. Stopping smoking improves respiratory defence and reduces pneumonia risk. Hand hygiene, covering coughs and avoiding close contact with vulnerable people while acutely unwell can reduce transmission of respiratory infections. People with swallowing difficulties may need assessment and an individual plan to reduce aspiration. This may involve speech and language therapy, oral care, positioning and review of food or fluid consistency. What this lesson should not be used for This lesson explains pneumonia as a disease. It cannot determine whether a particular cough, fever or chest pain is pneumonia. It should not be used to select antibiotics, interpret an oxygen reading alone or calculate a severity score at home. Seek clinical assessment when pneumonia is suspected, particularly when breathing, alertness, feeding or general condition is worsening.

Pneumonia affects the gas exchanging parts of the lungs. Bacteria and viruses are common causes, but symptoms alone may not reveal the organism. Clinicians combine the illness pattern, examination, oxygen level, severity assessment and appropriate investigations to decide how urgently the person needs care.