Every year, pneumonia affects more than 1.5 million Americans seriously enough to require an emergency department visit, and it remains one of the leading causes of hospitalization and death worldwide. Despite advances in antibiotics and vaccines, pneumonia kills approximately 50,000 people in the United States annually, making it the eighth leading cause of death. This lung infection demands respect — particularly for older adults, young children, and anyone with a weakened immune system. Understanding the different types, recognizing symptoms early, and knowing when to seek care can be the difference between a routine illness and a life-threatening one. For context on how respiratory conditions fit within broader health concerns, see our medical conditions guide.
What Is Pneumonia?
Pneumonia is an infection that inflames the air sacs (alveoli) in one or both lungs. The air sacs may fill with fluid or pus, causing cough with phlegm, fever, chills, and difficulty breathing. According to the National Heart, Lung, and Blood Institute, pneumonia can range from mild enough to treat at home to severe enough to require intensive care and mechanical ventilation.
The infection can be caused by bacteria, viruses, fungi, or, less commonly, parasites. The causative organism, how the infection was acquired, and the patient’s underlying health all influence the severity, treatment, and outcome. Pneumonia can affect one lobe of a lung (lobar pneumonia), patches throughout both lungs (bronchopneumonia), or the tissues between the air sacs (interstitial pneumonia).
It’s important to distinguish pneumonia from bronchitis. While both can cause cough and chest discomfort, bronchitis involves inflammation of the airways (bronchial tubes) without the fluid-filled air sacs that characterize pneumonia. Bronchitis is usually viral and self-limiting; pneumonia is more likely to cause significant fever, require treatment, and lead to serious complications.
Types of Pneumonia
Community-Acquired Pneumonia (CAP)
CAP is the most common type and refers to pneumonia acquired outside of a hospital or healthcare facility. Streptococcus pneumoniae (pneumococcus) is the leading bacterial cause. Other common bacterial causes include Haemophilus influenzae, Mycoplasma pneumoniae (which causes “walking pneumonia”), Chlamydophila pneumoniae, and Legionella pneumophila. Respiratory viruses — influenza, respiratory syncytial virus (RSV), SARS-CoV-2, and rhinoviruses — are also major causes, particularly during seasonal peaks.
Hospital-Acquired Pneumonia (HAP) and Ventilator-Associated Pneumonia (VAP)
HAP develops 48 hours or more after hospital admission in a patient not on mechanical ventilation at the time of admission. VAP develops more than 48 hours after intubation and mechanical ventilation. These are caused by different, often more resistant organisms — including Staphylococcus aureus (including MRSA), Pseudomonas aeruginosa, and Klebsiella pneumoniae — and carry higher mortality rates than community-acquired infections.
Aspiration Pneumonia
This type occurs when food, liquid, saliva, or vomit is inhaled into the lungs. It is most common in people with swallowing difficulties due to stroke, neurological disorders, heavy sedation, or alcohol intoxication. The infection involves both chemical injury from stomach acid and bacterial infection from oral flora. Aspiration pneumonia tends to affect the lower lobes of the lungs, particularly the right lower lobe.
Fungal Pneumonia
Caused by fungi such as Histoplasma, Coccidioides, Blastomyces, and Cryptococcus, fungal pneumonia typically occurs in specific geographic regions or in immunocompromised individuals. Pneumocystis jirovecii pneumonia (PJP) is a particularly important opportunistic infection in people with advanced HIV/AIDS or other forms of severe immunosuppression.
Symptoms and When They’re Serious
Pneumonia symptoms can develop suddenly or gradually, depending on the causative organism and the patient’s overall health. Classic symptoms include cough (often productive with yellow, green, or rust-colored sputum), fever (which may be high — 102 to 105 degrees Fahrenheit — or low-grade), chills and rigors, shortness of breath, and chest pain that worsens with deep breathing or coughing (pleuritic chest pain).
According to the CDC, additional symptoms can include fatigue, loss of appetite, confusion (especially in older adults), nausea, vomiting, and diarrhea. Older adults and people with weakened immune systems may present atypically — with confusion, falls, or functional decline rather than typical respiratory symptoms. A lower-than-normal body temperature is sometimes seen in elderly patients with pneumonia.
“Atypical” pneumonia caused by Mycoplasma, Chlamydophila, or certain viruses tends to have a more gradual onset with dry cough, low-grade fever, headache, and muscle aches. This milder presentation is the origin of the term “walking pneumonia” — though even these infections can occasionally become severe.
When to seek emergency care: Call 911 or go to the nearest emergency room if you experience severe difficulty breathing, chest pain, confusion or altered mental status, bluish discoloration of the lips or fingertips (cyanosis), a high fever that doesn’t respond to treatment, or coughing up blood. These signs indicate potentially life-threatening pneumonia requiring immediate intervention.
Diagnosis
Diagnosis begins with a physical examination. Your doctor will listen to your lungs with a stethoscope for abnormal sounds such as crackles (rales), which indicate fluid in the air sacs, and decreased breath sounds, which suggest consolidation (a section of lung filled with fluid or inflammatory material). Fever, elevated heart rate, and low oxygen saturation on pulse oximetry provide additional clinical clues.
Chest X-ray is the standard imaging study for confirming pneumonia. It can reveal the location and extent of the infection and help distinguish pneumonia from other causes of respiratory symptoms. According to the American Thoracic Society, a chest X-ray showing a new infiltrate in the setting of compatible symptoms is the clinical standard for diagnosis.
Blood tests typically include a complete blood count (white blood cell count is usually elevated), inflammatory markers (C-reactive protein, procalcitonin), and blood cultures to identify bacteria in the bloodstream. Sputum cultures can help identify the specific organism and guide antibiotic selection. In hospitalized patients, additional tests may include urinary antigen tests for Legionella and Streptococcus pneumoniae, viral PCR panels, and in severe cases, CT scan of the chest or bronchoscopy.
Treatment
Treatment depends on the type and severity of pneumonia, the likely causative organism, and the patient’s overall health. For outpatient management of community-acquired pneumonia in otherwise healthy adults, the Infectious Diseases Society of America recommends amoxicillin as first-line therapy for typical bacterial pneumonia, or a macrolide (azithromycin) or doxycycline when atypical organisms are suspected. Patients with comorbidities may require a respiratory fluoroquinolone or combination therapy.
Hospitalized patients with moderate to severe pneumonia receive intravenous antibiotics, supplemental oxygen to maintain adequate saturation, intravenous fluids, and close monitoring. The choice of antibiotics depends on severity scoring systems such as the CURB-65 or Pneumonia Severity Index (PSI), which help predict which patients need ICU-level care. Severely ill patients may require mechanical ventilation, vasopressors for septic shock, and treatment in the intensive care unit.
Viral pneumonia treatment is primarily supportive — rest, fluids, fever management, and oxygen as needed. Antiviral medications are available for certain viruses: oseltamivir for influenza pneumonia (most effective when started within 48 hours of symptom onset), and remdesivir or other antivirals for severe COVID-19 pneumonia. Antibiotics are not effective against viruses but may be prescribed if bacterial co-infection is suspected. Fungal pneumonia requires specific antifungal medications such as fluconazole, itraconazole, or amphotericin B.
Recovery: What to Expect
Recovery from pneumonia takes longer than many patients expect. While symptoms like fever may resolve within a few days of starting antibiotics, fatigue and reduced exercise tolerance often persist for weeks to months. The American Lung Association notes that it may take 6 to 8 weeks to return to your normal energy level after pneumonia, and chest X-ray abnormalities can take even longer to clear.
During recovery, getting adequate rest, staying hydrated, completing the full course of prescribed antibiotics, and gradually increasing activity are important. Avoid smoking and secondhand smoke exposure. Deep breathing exercises and incentive spirometry can help re-expand the lungs and prevent complications like atelectasis (collapse of lung tissue).
Follow-up chest X-ray is often recommended 6 to 12 weeks after pneumonia, particularly in smokers, older adults, and those with severe disease, to confirm resolution and rule out an underlying process such as lung cancer that may have been obscured by the infection. If symptoms are not improving within 3 to 5 days of treatment, contact your doctor — the antibiotic may need to be changed, or complications may have developed.
Prevention: Vaccines and Other Strategies
Vaccination is the single most effective pneumonia prevention strategy. The pneumococcal conjugate vaccine (PCV20, marketed as Prevnar 20) is now recommended by the CDC for all adults aged 65 and older and for younger adults with certain risk factors including chronic heart, lung, liver, or kidney disease, diabetes, immunocompromising conditions, cochlear implants, cerebrospinal fluid leaks, smoking, and alcoholism.
Annual influenza vaccination reduces the risk of viral pneumonia directly and bacterial pneumonia indirectly (influenza damages the airway lining, making bacterial superinfection more likely). COVID-19 vaccination reduces the risk of severe COVID pneumonia. RSV vaccines, approved in 2023 for older adults and pregnant individuals, add another layer of protection against a common respiratory pathogen.
Beyond vaccines, hand hygiene is the most basic and effective infection control measure. Avoiding close contact with people who are visibly ill, not smoking (smokers have significantly higher pneumonia rates), moderating alcohol intake, maintaining good oral hygiene (to reduce aspiration risk), and managing chronic conditions effectively all contribute to pneumonia prevention. Understanding the cost implications of hospitalization further underscores the value of preventive measures.
Pneumonia in Special Populations
Adults over 65 face the highest pneumonia mortality — the fatality rate for hospitalized elderly patients with pneumonia ranges from 10 to 30 percent. Age-related immune decline (immunosenescence), chronic diseases, reduced cough reflex, and higher aspiration risk all contribute. Pneumonia in older adults frequently precipitates functional decline, cognitive worsening, and loss of independence even after the acute infection resolves.
Children under 5, particularly those under 2, are also at elevated risk. According to the World Health Organization, pneumonia is the single largest infectious cause of death in children worldwide. In the United States, childhood pneumonia deaths have declined dramatically thanks to vaccines and antibiotics, but the disease still causes significant morbidity.
Immunocompromised patients — those with HIV/AIDS, organ transplants, active cancer treatment, or autoimmune diseases treated with immunosuppressive medications — are vulnerable to a wider range of organisms, including opportunistic infections that rarely affect healthy individuals. Their pneumonia may present atypically and progress rapidly, requiring a higher index of suspicion and more aggressive diagnostic workup.
Frequently Asked Questions
Is pneumonia contagious?
The organisms that cause pneumonia — bacteria, viruses, and fungi — can spread from person to person through respiratory droplets, direct contact, or environmental exposure. However, exposure to these organisms doesn’t necessarily cause pneumonia; in many cases, the same organism might cause only an upper respiratory infection or no illness at all. The development of pneumonia depends on the virulence of the organism, the dose of exposure, and the host’s immune defenses. Standard hygiene precautions — handwashing, covering coughs — reduce transmission risk.
How long does pneumonia last?
The timeline varies by type and severity. With appropriate antibiotics, bacterial pneumonia symptoms often begin improving within 48 to 72 hours, though full recovery takes 1 to 3 weeks for mild cases and 4 to 8 weeks or longer for severe cases. Viral pneumonia may last 1 to 3 weeks. Fatigue is typically the last symptom to resolve and can persist for months. If symptoms are not improving within 3 to 5 days of treatment, medical reassessment is needed.
Can you get pneumonia more than once?
Yes. Having pneumonia once does not provide lasting immunity against future episodes, especially since many different organisms can cause the infection. Recurrent pneumonia — defined as two or more episodes in a year or three or more episodes over any period — warrants investigation for underlying causes such as immunodeficiency, structural lung disease, aspiration, or an obstructing lesion like a tumor.
What is the difference between pneumonia and COVID-19?
COVID-19 is a specific viral infection caused by SARS-CoV-2 that can cause pneumonia as one of its manifestations. Not everyone with COVID-19 develops pneumonia — many have mild upper respiratory symptoms or no symptoms. When COVID-19 does cause pneumonia, it typically produces bilateral (both lungs) ground-glass opacities on imaging. Other viruses, bacteria, and fungi can also cause pneumonia. Treatment differs: COVID pneumonia may be treated with specific antivirals and anti-inflammatory drugs, while bacterial pneumonia requires antibiotics.
Should I go to the hospital for pneumonia?
Many cases of pneumonia in otherwise healthy adults can be treated safely at home with oral antibiotics. You should seek hospital care if you have severe shortness of breath, oxygen levels below 94 percent (if you have a pulse oximeter), high fever unresponsive to treatment, inability to keep fluids or medications down, confusion, or significant underlying health conditions. Your doctor can use severity scoring tools to help determine whether outpatient or inpatient treatment is appropriate for your situation.
Protecting Yourself and Your Family
Pneumonia is both common and preventable in many cases. The most impactful step you can take is staying current on recommended vaccines — pneumococcal, influenza, COVID-19, and RSV vaccines each target major pneumonia-causing pathogens. If you’re over 65, have chronic diseases, smoke, or are immunocompromised, talk to your doctor about your vaccination status at your next visit.
If you’re diagnosed with pneumonia, follow your treatment plan closely. Take all prescribed medications for the full course. Rest, hydrate, and give your body the time it needs to recover — pneumonia is not a condition to push through. Monitor for worsening symptoms, and don’t hesitate to call your doctor if you’re not improving as expected.
For caregivers of high-risk individuals — elderly parents, young children, immunocompromised family members — vigilance matters. Early recognition of pneumonia symptoms, prompt medical evaluation, and preventive measures like vaccination and aspiration precautions can meaningfully reduce the burden of this age-old but still dangerous disease.