Lung Infection

What is lung infection?

A lung infection is an illness in which germs such as bacteria, viruses, or fungi get into the lungs and cause inflammation (swelling and irritation of tissue). The lungs are the two spongy organs in the chest that move oxygen into the blood and remove carbon dioxide. When they become infected, the small air sacs (alveoli) and the airways that lead to them may fill with fluid, mucus, or pus, making it harder to breathe and to get enough oxygen.

“Lung infection” is a broad, everyday term rather than a single diagnosis. The most common type is pneumonia, an infection of the air sacs themselves. Other conditions often grouped under this term include acute bronchitis (infection of the larger airways, the bronchi), bronchiolitis (infection of the smallest airways, seen mainly in infants), tuberculosis (a slow-developing bacterial infection), and fungal lung infections, which are less common and usually affect people with weakened immune systems. A lung abscess, a pocket of pus inside the lung, is a rarer complication of infection.

Lung infections can affect anyone, at any age. They are more frequent and tend to be more serious in very young children, adults over about 65, people with long-term heart or lung disease, smokers, and people whose immune systems are weakened by illness or medication. Many mild lung infections clear on their own or with simple treatment, while others require hospital care. In a hospital setting, these conditions are usually managed by a pulmonology department (the specialty that deals with the lungs and breathing), often together with infectious disease and, when needed, intensive care specialists. This page explains what a lung infection is, common lung infection symptoms and causes, how doctors reach a diagnosis, and the main lung infection treatment options.

Symptoms of a lung infection

Lung infection symptoms depend on the germ involved, which part of the lung is affected, and the person’s age and general health. Symptoms may appear suddenly over a day or two, as often happens with bacterial pneumonia, or build gradually over a week or more, which is more typical of some viral and so-called “atypical” infections. Common lung infection symptoms include:

• Cough, which may be dry or may produce mucus (phlegm) that is clear, yellow, green, or occasionally streaked with blood
• Fever, chills, and sweating
• Shortness of breath, or breathing that feels faster or more effortful than usual
• Chest pain, often sharp and worse when breathing in deeply or coughing (this is called pleuritic pain)
• Wheezing or a whistling sound when breathing, more common in bronchitis and bronchiolitis
• Fatigue and general weakness
• Muscle aches and headache
• Loss of appetite
• Rapid heartbeat
• Bluish or gray lips or fingertips, a sign of low oxygen that always needs urgent attention

Symptoms can look different in certain groups. Older adults may have little or no fever and may instead become confused, unusually drowsy, or unsteady on their feet. Babies and young children may feed poorly, breathe very quickly, grunt, flare their nostrils, or pull in the skin between the ribs with each breath. People with weakened immune systems may develop a serious infection with only subtle early signs.

The stage of the illness also matters. Early on, a lung infection may feel like a bad cold or the flu. As it progresses, breathing symptoms usually become more prominent. Some infections, such as tuberculosis, develop slowly over weeks or months and may cause night sweats, weight loss, and a persistent cough rather than a sudden fever. A cough that lingers for several weeks after other symptoms improve is common and does not always mean the infection is still active, but it should be checked if it is not clearly improving.

Causes and risk factors

Lung infection causes fall into three main groups: viruses, bacteria, and fungi. Which germ is responsible often influences how the illness behaves and how it is treated.

• Viruses are the most frequent cause overall, especially in children. Common examples include influenza (flu) viruses, respiratory syncytial virus (RSV), rhinoviruses that cause colds, and coronaviruses, including the virus that causes COVID-19. Viral infections sometimes weaken the lungs’ defenses and allow a bacterial infection to follow.
• Bacteria are a common cause of pneumonia in adults. Streptococcus pneumoniae (pneumococcus) is a leading cause. Others include Haemophilus influenzae, Staphylococcus aureus, and bacteria such as Mycoplasma pneumoniae and Legionella, which cause what doctors call atypical pneumonia. Mycobacterium tuberculosis is the bacterium that causes tuberculosis.
• Fungi are a less common cause and mostly affect people with weakened immune systems or those exposed to large amounts of fungal spores in soil or bird droppings. Examples include Aspergillus, Histoplasma, and Pneumocystis.

Germs usually reach the lungs by being breathed in from the air after an infected person coughs or sneezes, or by traveling down from the nose and throat. In some cases, food, drink, saliva, or vomit is accidentally inhaled into the lungs, which is called aspiration; the germs carried with it can cause aspiration pneumonia. This is more likely in people with swallowing problems, reduced consciousness, or heavy alcohol use.

Doctors also describe lung infections by where they were acquired. Community-acquired infections start in everyday life. Hospital-acquired infections begin during a hospital stay and are sometimes caused by bacteria that are harder to treat. Ventilator-associated pneumonia can develop in people who are on a breathing machine in intensive care.

Several factors increase the risk of getting a lung infection or of having a more severe illness:

• Age under 2 years or over about 65 years
• Smoking, including exposure to secondhand smoke
• Chronic lung conditions such as chronic obstructive pulmonary disease (COPD), asthma, bronchiectasis, or cystic fibrosis
• Heart disease, diabetes, kidney disease, or liver disease
• A weakened immune system due to HIV, cancer treatment, organ transplant medicines, or long-term steroid use
• A recent viral illness such as a cold or the flu
• Difficulty swallowing or reduced consciousness, which raise the risk of aspiration
• Heavy alcohol use or poor nutrition
• Recent hospital stay, surgery, or being on a ventilator
• Crowded living conditions or close contact with someone who has tuberculosis

Diagnosis of a lung infection

Lung infection diagnosis begins with a conversation and a physical examination. Your doctor will ask about your symptoms, how quickly they started, any recent travel or contact with sick people, your smoking history, and other medical conditions. During the examination, the doctor will listen to your lungs with a stethoscope for crackling, bubbling, or wheezing sounds, and will check your temperature, breathing rate, heart rate, and blood pressure. A small clip placed on a fingertip (pulse oximeter) measures the oxygen level in your blood.

Depending on how unwell you are, further tests may be used to confirm the diagnosis, identify the cause, and judge severity:

• Chest X-ray: the most common imaging test. It can show areas of the lung that look cloudy or dense because they are filled with fluid or pus, which supports a diagnosis of pneumonia and helps show how much of the lung is involved.
• Blood tests: a complete blood count can show whether white blood cells (infection-fighting cells) are raised. Other blood tests measure markers of inflammation and check kidney and liver function. Blood cultures may be taken to see whether bacteria have spread into the bloodstream.
• Sputum tests: a sample of mucus coughed up from the lungs can be examined under a microscope and cultured (grown in a laboratory) to identify the germ and find out which antibiotics it responds to. Special tests on sputum are used to look for tuberculosis.
• Nose and throat swabs: rapid tests can detect viruses such as influenza, RSV, and the COVID-19 virus.
• Urine tests: certain urine tests can detect pneumococcus or Legionella.
• CT scan of the chest: a more detailed imaging test that may be used when the X-ray is unclear, when symptoms are not improving, or when a complication such as an abscess or fluid around the lung is suspected.
• Bronchoscopy: a thin, flexible tube with a camera is passed through the nose or mouth into the airways so the doctor can look inside and collect samples. This is reserved for more complex or unexplained cases.
• Pleural fluid sampling: if fluid has built up between the lung and the chest wall (a pleural effusion), a needle may be used to remove some for testing.

Doctors often use scoring tools that combine age, confusion, breathing rate, blood pressure, and certain blood results to estimate how severe a pneumonia is and whether it is safer to treat at home or in the hospital. In many mild cases, particularly in otherwise healthy people, treatment is started based on symptoms and examination alone, without every test on this list.

Treatment options for a lung infection

Lung infection treatment options depend on the likely cause, how severe the illness is, and the person’s age and overall health. The aims are to clear the infection, support breathing and oxygen levels, relieve symptoms, and prevent complications.

Observation and self-care. Many viral lung infections, including most cases of acute bronchitis, do not respond to antibiotics and are managed by resting, drinking enough fluids, and using simple measures to ease symptoms while the body clears the virus. Your doctor may advise a follow-up visit if symptoms are not improving within a set period or if they worsen.

Medications.

• Antibiotics are used when a bacterial infection is suspected or confirmed. The choice depends on the likely bacteria, local patterns of antibiotic resistance, allergies, and where the infection was acquired. It is important to take the full course as prescribed, even if you feel better sooner, unless your doctor tells you otherwise. Tuberculosis requires a specific combination of antibiotics taken for several months.
• Antiviral medicines may be prescribed for some viral infections, such as influenza or COVID-19, particularly when started early or in people at higher risk of severe illness.
• Antifungal medicines are used for fungal lung infections and are usually managed by specialists.
• Symptom relief may include medicines to reduce fever and ease pain, and in some cases inhaled medicines (bronchodilators) that relax the airways to help wheezing. Cough suppressants are used cautiously because coughing helps clear mucus from the lungs.

Hospital care and procedures. People who are very short of breath, have low oxygen levels, are confused, cannot keep fluids down, or have other serious conditions may be admitted to the hospital. Treatment there can include oxygen given through a mask or nasal tubes, fluids and antibiotics given through a vein, and close monitoring. In severe cases, breathing support may be needed, ranging from high-flow oxygen to non-invasive ventilation (a tight-fitting mask connected to a machine) or, in intensive care, mechanical ventilation through a breathing tube. If infected fluid collects around the lung (an empyema), it may need to be drained with a tube placed through the chest wall.

Surgery. Surgery is rarely needed for lung infections. It is generally reserved for complications that do not resolve with medicines and drainage, such as a persistent lung abscess or thick, infected fluid around the lung that cannot be cleared with a chest tube.

Rehabilitation and recovery. After a serious lung infection, recovery can take weeks. A physiotherapist may teach breathing and coughing techniques to help clear mucus and rebuild stamina. For people with underlying lung disease, a structured pulmonary rehabilitation program, which combines supervised exercise and education, may be recommended. A follow-up chest X-ray is sometimes arranged to confirm that the lungs have cleared, particularly in older adults and smokers.

Living with a lung infection and outlook

For most otherwise healthy people, the outlook after a lung infection is good. Fever often settles within a few days of starting appropriate treatment, though cough and tiredness commonly last for several weeks. Feeling “back to normal” can take longer than expected, and this does not usually mean something has gone wrong. Gradually increasing activity, getting enough rest and fluids, and avoiding smoke are reasonable steps during recovery.

The outlook is less predictable in older adults, in people with long-term heart or lung disease, and in those with weakened immune systems. In these groups, a lung infection can be serious and may lead to complications such as fluid around the lung, a lung abscess, spread of infection into the bloodstream (sepsis), or worsening of existing conditions. Some people, especially after severe illness or intensive care, experience lasting breathlessness, weakness, or low mood, and may benefit from ongoing support and rehabilitation.

Repeated lung infections are a reason to look for an underlying cause, such as an undiagnosed airway disease, a swallowing problem, or an immune condition. Your doctor may suggest further tests in this situation. Because no one can guarantee how an individual illness will progress, attending follow-up appointments and reporting new or worsening symptoms promptly are the most reliable ways to protect your recovery.

Some lung infections can be reduced in likelihood, though not entirely prevented. Vaccines are available against several common causes, including influenza, pneumococcus, RSV for certain age groups, and COVID-19; your doctor can advise which are appropriate for you. Not smoking, washing hands regularly, and managing long-term conditions well also help lower risk.

Frequently asked questions

What is lung infection and is it the same as pneumonia?

“Lung infection” is a general term for any infection involving the lungs or the airways inside them, while pneumonia is a specific type of lung infection affecting the air sacs where oxygen passes into the blood. Pneumonia is the most common serious lung infection, but bronchitis, bronchiolitis, tuberculosis, and fungal infections are also lung infections. Your doctor will usually give a more specific diagnosis after examining you and, if needed, arranging tests.

What are the first lung infection symptoms to watch for?

Early lung infection symptoms often resemble a cold or the flu: cough, tiredness, mild fever, and body aches. Signs that the infection may be affecting the lungs more seriously include shortness of breath, chest pain when breathing in, a cough producing colored or blood-streaked mucus, and a high or persistent fever. In older adults, new confusion or drowsiness can be an early sign even without fever.

What are the most common lung infection causes?

Viruses such as influenza, RSV, and the COVID-19 virus are the most frequent lung infection causes overall. Bacteria, particularly pneumococcus, are a common cause of pneumonia in adults. Fungi are a rarer cause and mainly affect people with weakened immunity. Accidentally inhaling food, drink, or vomit can also introduce germs into the lungs and cause aspiration pneumonia.

How is lung infection diagnosis confirmed?

Lung infection diagnosis usually starts with a physical examination, including listening to the lungs and checking oxygen levels with a finger sensor. A chest X-ray is the most common test used to confirm pneumonia. Blood tests, sputum cultures, and nose or throat swabs may be used to identify the germ and assess severity. In complex cases, a CT scan or bronchoscopy may be needed.

What are the main lung infection treatment options?

Lung infection treatment options range from rest, fluids, and symptom relief for mild viral infections, to antibiotics for bacterial infections, antivirals for certain viruses, and antifungal medicines for fungal infections. More severe illness may require hospital care with oxygen, intravenous medicines, and breathing support. Procedures or surgery are reserved for complications such as infected fluid around the lung or an abscess.

Can a lung infection go away on its own?

Many mild lung infections, especially viral bronchitis, do improve without specific treatment as the body’s immune system clears the virus. However, bacterial pneumonia usually needs antibiotics, and delaying treatment can allow the infection to worsen. It is difficult to tell viral from bacterial infection based on symptoms alone, so a medical assessment is advisable if symptoms are more than mild or are not improving.

How long does it take to recover from a lung infection?

Recovery time varies with the cause, severity, and the person’s health. Fever often improves within a few days of effective treatment, but cough and fatigue commonly persist for several weeks. After a severe infection or a hospital stay, full recovery can take a month or longer. If symptoms are not steadily improving, or if they return after getting better, a follow-up assessment is recommended.

When to see a doctor

Many mild respiratory illnesses can be managed at home, but a lung infection can worsen quickly, particularly in young children, older adults, and people with long-term health conditions. See a doctor if you have a cough with fever lasting more than a few days, a cough producing colored or bloody mucus, chest pain when breathing, or any symptoms that are getting worse rather than better. Seek help sooner if you are over 65, pregnant, or have a heart, lung, or immune condition.

Seek urgent or emergency care if you or someone you are caring for has any of the following red-flag signs:

• Severe difficulty breathing, breathlessness at rest, or being unable to speak in full sentences
• Blue, gray, or very pale lips, face, or fingertips
• Chest pain that is severe, persistent, or accompanied by a racing heartbeat
• Coughing up significant amounts of blood
• New confusion, extreme drowsiness, fainting, or difficulty waking
• A very high fever that does not come down, or a fever with shaking chills and a rapid pulse
• Signs of dehydration, such as passing very little urine, or being unable to keep fluids down
• In babies: rapid or labored breathing, grunting, pauses in breathing, poor feeding, or unusual floppiness or irritability
• Symptoms that improve and then suddenly worsen

These signs may indicate low oxygen levels, sepsis, or another serious complication that needs prompt medical evaluation. This page is for general information only and does not replace assessment by a qualified clinician.