Pneumonia is an infection that inflames the tiny air sacs of the lungs, which can fill with fluid or pus and make breathing difficult. It ranges from a mild illness that clears up at home to a serious, even life-threatening condition, especially in young children, older adults, and people with chronic health problems. Because it can be caused by bacteria, viruses, or fungi, and because vaccines now prevent some of the most dangerous forms, knowing the symptoms, when to seek care, and how pneumonia is diagnosed and treated is genuinely useful. This guide explains what pneumonia is, its causes and types, symptoms and warning signs, how it is diagnosed, treatment, prevention including recent vaccine changes, and the latest research.
What is pneumonia?
Pneumonia is an infection of the lungs that inflames the air sacs, called alveoli, where oxygen passes into the blood. When these sacs fill with fluid or pus, the lungs cannot move oxygen as efficiently, which causes cough, fever, and shortness of breath. Pneumonia can affect one or both lungs, and it varies widely in severity depending on the germ involved and the person’s overall health.
Most otherwise healthy adults recover from pneumonia within one to three weeks, but it can be dangerous for people at higher risk, and it remains a leading cause of hospitalization. Doctors also classify pneumonia by where it was caught: community-acquired pneumonia develops in everyday life, while hospital-acquired and ventilator-associated pneumonia occur in healthcare settings and more often involve harder-to-treat, resistant bacteria.
Causes and types of pneumonia
Pneumonia has several causes, and identifying the likely type helps guide treatment.
| Type | What causes it |
|---|---|
| Bacterial pneumonia | Bacteria, most commonly Streptococcus pneumoniae; can cause high fever and rapid illness |
| Viral pneumonia | Viruses such as influenza, RSV, and COVID-19; often starts more gradually with flu-like symptoms |
| Walking pneumonia | A milder, atypical form usually caused by Mycoplasma bacteria |
| Fungal pneumonia | Fungi; less common and mainly affects people with weakened immune systems |
Some cases follow another respiratory infection, which is one reason a bout of the flu can sometimes lead to pneumonia. Understanding the difference between the illnesses helps, and this guide to the symptoms and course of the flu explains a common viral trigger. People with chronic lung disease are also more vulnerable, including those with the airflow limitation of chronic obstructive pulmonary disease.
Symptoms of pneumonia
Pneumonia symptoms range from mild to severe and often include a cough that may bring up phlegm, fever, chills, shortness of breath, rapid or shallow breathing, and chest pain that worsens with breathing or coughing. Fatigue, sweating, nausea, and a loss of appetite are common too. Bacterial pneumonia can cause a sudden high fever, while viral pneumonia often begins more gradually with flu-like symptoms.
Warning signs that call for urgent medical care include difficulty breathing, chest pain, a high or persistent fever, and bluish lips or fingertips. In adults 65 and older, a key and easily missed sign is new confusion or a change in mental awareness, which may be more prominent than cough or fever. Anyone who is very short of breath or getting rapidly worse should seek emergency care.
Who is at higher risk
Anyone can get pneumonia, but some groups are at higher risk of serious illness. These include children under 2, adults 65 and older, people who smoke, and those with chronic heart or lung conditions, diabetes, or weakened immune systems. Recent hospitalization or a viral respiratory infection can also raise the risk. For people in these groups, pneumonia is more likely to require hospital care, which makes prevention and early treatment especially important.
How pneumonia is diagnosed
Doctors diagnose pneumonia by combining a physical exam, listening for abnormal crackling sounds in the lungs, with a chest X-ray that confirms the infection and shows where it is. In more complex or severe cases, a CT scan may be used. Pulse oximetry, a clip on the finger, checks whether the infection is lowering blood oxygen levels.
Blood tests help confirm infection and gauge how the body is responding. A white blood cell count, along with markers of inflammation such as C-reactive protein and procalcitonin, can support the diagnosis and help distinguish bacterial from viral pneumonia, which guides whether antibiotics are needed. Understanding the inflammation measured by a CRP test and the bacterial-infection signal from a procalcitonin test shows why these values matter. Sputum and blood cultures can identify the specific organism in more serious cases, and severity tools such as CURB-65 help decide whether someone can be treated at home or needs the hospital. Learning how to read the flags and reference ranges on a lab report makes these results easier to follow.
Treatment options for pneumonia
Treatment depends on the cause and severity. Bacterial pneumonia is treated with antibiotics, and it is important to finish the full course even after feeling better. Viral pneumonia does not respond to antibiotics; some cases, such as influenza, may be treated with antiviral medicine, and most viral pneumonia is managed with supportive care. Rest, fluids, and fever and pain relievers help recovery across the board.
| Approach | Role |
|---|---|
| Antibiotics | Treat bacterial pneumonia; the full course should be completed |
| Antivirals | Used for some viral pneumonia, such as influenza, when appropriate |
| Supportive care | Rest, fluids, fever and pain relief, and oxygen when needed |
| Hospital care | Oxygen, intravenous fluids, and monitoring for severe or high-risk cases |
People who are older, confused, short of breath, or have low oxygen or unstable vital signs may need hospital care, which can include oxygen, intravenous fluids, and closer monitoring. When a severe lung infection triggers a body-wide response, it can progress toward the dangerous reaction described in sepsis, which is why prompt treatment of serious pneumonia matters so much.
Preventing pneumonia
Vaccines are among the most effective ways to prevent pneumonia and its complications. Pneumococcal vaccines protect against the most common bacterial cause, and staying current with the annual flu vaccine and COVID-19 vaccination reduces viral pneumonia and the secondary bacterial pneumonia that can follow. Handwashing, not smoking, and managing chronic conditions all lower risk as well.
Guidance on the pneumococcal vaccine has recently expanded. In late 2024, US advisers lowered the recommended age for routine pneumococcal vaccination from 65 to 50, meaning more adults now qualify for a single dose, and newer higher-valency vaccines cover more strains of the bacteria than older versions. Talking with a clinician about which vaccine is right for you, based on age and health, is a simple step with a large payoff.
Latest scientific advances in pneumonia research
Recent developments have reshaped both prevention and antibiotic use. According to PubMed-indexed research, a 2025 report in the CDC’s Morbidity and Mortality Weekly Report described the decision to lower the recommended age for pneumococcal vaccination to 50, noting that serious pneumococcal disease in adults aged 50 to 64 approaches the rate seen in those 65 and older, while far fewer in the younger group had been vaccinated (Kobayashi et al., 2025). What this means for you: many adults now qualify for a pneumococcal vaccine a decade earlier than before, closing a protection gap.
A 2026 randomized trial in Clinical Infectious Diseases found that turning procalcitonin and viral test results into a clear estimate of the probability of bacterial pneumonia helped doctors safely cut antibiotic use by about four days per hospitalized patient, without more complications (Baghdadi et al., 2026). What this means for you: smarter use of blood tests can reduce unnecessary antibiotics, which benefits both patients and the broader fight against antibiotic resistance. A 2026 registry study in Infectious Diseases and Therapy underscored that older adults bear the heaviest burden of pneumococcal disease and that newer, higher-valency vaccines cover more of the strains involved (Kononoff et al., 2026). What this means for you: age alone is a strong reason to stay current on pneumococcal vaccination, and newer vaccines offer broader protection.
Glossary of key pneumonia terms
| Term | Definition |
|---|---|
| Alveoli | The tiny air sacs in the lungs where oxygen enters the blood. |
| Community-acquired pneumonia | Pneumonia caught in everyday life, outside a hospital. |
| Walking pneumonia | A milder, atypical pneumonia often caused by Mycoplasma bacteria. |
| Procalcitonin | A blood marker that rises with bacterial infection and can guide antibiotics. |
| Pulse oximetry | A finger clip that measures the oxygen level in the blood. |
| Pneumococcal vaccine | A vaccine that protects against the most common bacterial cause of pneumonia. |
| CURB-65 | A tool that gauges pneumonia severity to guide home versus hospital care. |
Frequently asked questions about pneumonia
What is pneumonia and how does it affect the lungs?
Pneumonia is an infection that inflames the air sacs of the lungs, which can fill with fluid or pus. This makes it harder for oxygen to reach the blood, causing cough, fever, and shortness of breath. It can be caused by bacteria, viruses, or fungi and ranges from mild to severe.
Is pneumonia contagious?
The germs that cause many types of pneumonia can spread from person to person through respiratory droplets from coughs and sneezes, so bacterial and viral pneumonia can be contagious. Fungal pneumonia is not spread between people. Good hand hygiene and staying home when sick reduce spread.
What is walking pneumonia and how is it different?
Walking pneumonia is a milder form, usually caused by Mycoplasma bacteria, in which people feel unwell but can often keep up daily activities. Symptoms tend to be less severe than typical pneumonia, but it can still linger and sometimes needs antibiotics.
What are the warning signs that need emergency care?
Seek urgent care for difficulty breathing, chest pain, bluish lips or fingertips, a high or persistent fever, or, especially in older adults, new confusion. Rapidly worsening symptoms or severe shortness of breath are emergencies.
How is pneumonia diagnosed?
Doctors use a physical exam and a chest X-ray to confirm pneumonia, along with pulse oximetry to check oxygen. Blood tests such as a white blood cell count, C-reactive protein, and procalcitonin help assess the infection, and cultures can identify the specific germ in more serious cases.
Who should get the pneumonia vaccine, and at what age?
Pneumococcal vaccines are recommended for young children, adults with certain health conditions, and, following a recent update, all adults starting at age 50. An annual flu vaccine and staying current on COVID-19 vaccination also help prevent pneumonia. A clinician can advise on the right vaccine for you.
Sources
- Centers for Disease Control and Prevention — About Pneumonia — CDC, 2024 — cdc.gov
- Mayo Clinic Staff — Pneumonia: Symptoms and Causes — Mayo Clinic, 2024 — mayoclinic.org
- American Lung Association — Pneumonia Symptoms and Diagnosis — American Lung Association, 2024 — lung.org
- Kobayashi M, et al. — Expanded Recommendations for Use of Pneumococcal Conjugate Vaccines Among Adults Aged ≥50 Years — MMWR Morbidity and Mortality Weekly Report, 2025 — doi.org/10.15585/mmwr.mm7401a1
- Baghdadi JD, et al. — Using Probability of Community-Acquired Pneumonia to Tailor Antimicrobials Among Inpatients: A Pragmatic, Randomized Trial — Clinical Infectious Diseases, 2026 — doi.org/10.1093/cid/ciag126
- Kononoff J, et al. — Burden of Invasive Pneumococcal Disease and Community-Acquired Pneumonia in Adults — Infectious Diseases and Therapy, 2026 — doi.org/10.1007/s40121-026-01357-w
Further reading
- Understand a common viral illness that can lead to pneumonia in this guide to the symptoms and treatment of the flu.
- Learn about a chronic lung disease that raises pneumonia risk in this guide to chronic obstructive pulmonary disease.
- See how a severe infection can become body-wide in this guide to the warning signs of sepsis.
- See how doctors track infection and inflammation in this guide to the CRP blood test.
- Build confidence reading test results with this guide to reference ranges, flags, and next steps on a lab report.
Understand your lab results with BloodSense
Pneumonia care leans on lab values to answer practical questions: is this infection bacterial or viral, how is the body responding, and how severe is it. A white blood cell count, C-reactive protein, and procalcitonin, read together with oxygen levels, help guide whether antibiotics and hospital care are needed. BloodSense translates a full lab report into plain language, showing where each marker sits against its reference range and helping you track changes as you recover instead of reading one line in isolation.
