```html

Lung Infection (Pneumonia, Bronchitis, and Other Respiratory Infections)

What is Lung Infection?

A lung infection, also called a lower respiratory tract infection, is an inflammation of the lung tissue caused by microorganisms (bacteria, viruses, fungi, or parasites) or by irritants that trigger an immune response. The infection may involve the airways (bronchi), the alveoli (tiny air sacs where gas exchange occurs), or both. Common clinical entities that fall under the umbrella term “lung infection” include pneumonia, acute bronchitis, atypical pneumonia, and certain fungal or mycobacterial infections.<sup>1</sup> The condition can range from mild, self‑limited illness to a life‑threatening disease, especially in the very young, the elderly, and people with chronic health problems.

Common Causes

Many different pathogens and non‑infectious triggers can produce a lung infection. The most frequent culprits are:

• Bacterial pneumonia – Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus (including MRSA), Klebsiella pneumoniae.
• Viral infections – Influenza A/B, respiratory syncytial virus (RSV), coronavirus (including SARS‑CoV‑2), adenovirus, parainfluenza.
• Atypical (walking) pneumonia – Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila.
• Acute bronchitis – Usually viral (rhinovirus, coronavirus) but can be bacterial in smokers.
• Fungal infections – Histoplasma capsulatum, Coccidioides immitis, Aspergillus species (more common in immunocompromised hosts).
• Mycobacterial infection – Mycobacterium tuberculosis (TB) and non‑tuberculous mycobacteria (NTM).
• Aspiration pneumonia – Inhalation of oropharyngeal secretions containing anaerobic bacteria; common after binge drinking or in patients with dysphagia.
• Healthcare‑associated infection – Ventilator‑associated pneumonia (VAP) and hospital‑acquired pneumonia (HAP) caused by multidrug‑resistant organisms.
• Environmental/chemical irritants – Inhalation of toxic gases, smoke, or dust can provoke a secondary infection in already inflamed lungs.
• Immune‑mediated reactions – Certain autoimmune diseases (e.g., rheumatoid arthritis) can predispose to lung infection by impairing clearance mechanisms.

Associated Symptoms

Symptoms often overlap with other respiratory illnesses, but a lung infection typically produces a constellation of the following:

• Fever and chills (often >38 °C/100.4 °F)
• Productive cough with sputum that may be clear, yellow, green, rusty, or even bloody
• Chest pain that worsens with deep breathing or coughing (pleuritic pain)
• Shortness of breath or rapid breathing (tachypnea)
• Fatigue, malaise, and loss of appetite
• Headache and muscle aches (especially with viral causes)
• Wheezing or a “rattling” sound in the lungs
• Confusion or altered mental status in older adults
• Night sweats and weight loss (more common with TB or fungal infections)

When to See a Doctor

Most healthy adults recover from a mild bronchitis or viral pneumonia at home, but you should seek medical care promptly if you experience any of the following:

• Persistent fever > 38.5 °C (101.3 °F) lasting more than 48 hours
• Shortness of breath that interferes with talking or walking
• Chest pain that is sharp, persistent, or worsens when you lie down
• Rapid heart rate (> 100 bpm) or breathing rate (> 20 breaths/min)
• New confusion, dizziness, or a sudden change in mental status
• Sputum that is thick, foul‑smelling, or contains blood
• Symptoms that worsen after 3–5 days of home care
• Underlying conditions such as COPD, heart disease, diabetes, asthma, immunosuppression, or being over 65 years old

If you fall into any of these categories, contact your primary‑care provider, urgent‑care clinic, or go to the emergency department.

Diagnosis

Healthcare professionals use a combination of history, physical examination, and targeted testing to confirm a lung infection and determine its cause.

History & Physical Exam

• Questions about symptom onset, exposure history (travel, sick contacts, occupational hazards), smoking status, and vaccination record.
• Chest auscultation for crackles, wheezes, or diminished breath sounds.
• Measurement of oxygen saturation (pulse oximetry) and vital signs.

Imaging

• Chest X‑ray – First‑line test; shows infiltrates, consolidation, or pleural effusion.
• Chest CT scan – Provides detailed images if the X‑ray is inconclusive or complications are suspected.

Laboratory Tests

• Complete blood count (CBC) – Elevated white blood cells suggest bacterial infection.
• Blood cultures – Important for severe cases or suspected bacteremia.
• Sputum Gram stain and culture – Helps identify bacterial pathogens.
• Polymerase chain reaction (PCR) panels – Rapid detection of viral and atypical bacteria.
• Urinary antigen tests for Legionella and Streptococcus pneumoniae.
• Serology or interferon‑gamma release assays (IGRA) for tuberculosis.
• Fungal biomarkers (e.g., galactomannan, β‑D‑glucan) when fungal infection is suspected.

Functional Evaluation

• Arterial blood gas (ABG) if oxygenation is a concern.
• Pulmonary function tests (PFTs) after the acute phase to assess residual damage.

Treatment Options

Treatment depends on the underlying cause, severity, patient age, and comorbidities. The main goals are to eradicate the pathogen, relieve symptoms, and prevent complications.

Antimicrobial Therapy

• Bacterial pneumonia – Empiric antibiotics are started before culture results. Common regimens include:
  • Amoxicillin or amoxicillin‑clavulanate (outpatient, low‑risk)
  • Macrolide (azithromycin or clarithromycin) or doxycycline for atypical coverage
  • Respiratory fluoroquinolone (levofloxacin, moxifloxacin) for high‑risk or resistant organisms
• Viral infections – Antiviral drugs are indicated for influenza (oseltamivir, baloxavir) and for COVID‑19 (nirmatrelvir‑ritonavir, remdesivir) when criteria are met. Most other viral pneumonias are self‑limited and managed with supportive care.
• Fungal infections – Oral itraconazole, fluconazole, or systemic agents such as voriconazole or amphotericin B for severe disease.
• Mycobacterial infection – Multi‑drug regimens (rifampin, isoniazid, pyrazinamide, ethambutol for TB) administered for 6‑12 months.

Supportive Care

• Rest and adequate hydration (2‑3 L of fluids per day unless contraindicated).
• Fever reducers – Acetaminophen or ibuprofen as needed.
• Bronchodilators (short‑acting β2‑agonists) for wheezing or underlying COPD/asthma.
• Supplemental oxygen if SpO₂ < 92 % (target 94‑98 % for most patients).
• Chest physiotherapy or incentive spirometry to improve ventilation in hospitalized patients.

Hospital‑Based Interventions (Severe Cases)

• Intravenous antibiotics or antivirals.
• High‑flow nasal cannula, non‑invasive ventilation, or mechanical ventilation.
• Intravenous fluids and electrolyte management.
• Management of complications (e.g., empyema drainage, pleural effusion thoracentesis).

Home‑Based Strategies

• Complete the full prescribed course of antibiotics, even if symptoms improve.
• Use a humidifier or take warm steamy showers to loosen mucus.
• Elevate the head of the bed 30‑45° to reduce coughing at night.
• Avoid smoking and secondhand smoke; use a mask in polluted environments.

Prevention Tips

Many lung infections are avoidable with simple, evidence‑based measures:

• Vaccination: Annual influenza vaccine, COVID‑19 booster, pneumococcal vaccines (PCV13, PPSV23) for adults ≥ 65 years or high‑risk groups.
• Hand hygiene: Wash hands with soap and water for at least 20 seconds, especially after being in public places.
• Respiratory etiquette: Cover coughs/sneezes with a tissue or elbow; dispose of tissues promptly.
• Avoid smoking: Quit smoking and stay away from secondhand smoke, which impairs mucociliary clearance.
• Healthy lifestyle: Balanced diet, regular exercise, adequate sleep, and optimal control of chronic conditions (diabetes, heart disease, COPD).
• Indoor air quality: Use HEPA filters, keep humidity between 30‑50 %, and avoid mold or damp environments.
• Travel precautions: When traveling to endemic areas (e.g., for histoplasmosis or coccidioidomycosis), stay out of dust storms and use masks.
• Prompt treatment of upper‑respiratory infections: Early antiviral treatment for flu can reduce progression to pneumonia.

Emergency Warning Signs

If any of the following develop, seek emergency medical care (call 911 or go to the nearest ER) immediately:

• Severe difficulty breathing or feeling “air‑hungry.”
• Chest pain that radiates to the arm, jaw, or back, or that is associated with sweating.
• Bluish discoloration of lips, fingertips, or face (cyanosis).
• Sudden drop in blood pressure or fainting.
• Rapid, irregular heartbeat (palpitations) especially with dizziness.
• Confusion, agitation, or severe lethargy.
• High fever (> 40 °C/104 °F) that does not respond to antipyretics.
• Persistent vomiting or inability to keep fluids down, leading to dehydration.

---

Sources:

1. Mayo Clinic. “Pneumonia.” https://www.mayoclinic.org.
2. CDC. “Prevention & Treatment of Influenza.” https://www.cdc.gov.
3. National Heart, Lung, & Blood Institute. “Pneumonia Treatment and Care.” https://www.nhlbi.nih.gov.
4. World Health Organization. “Tuberculosis.” https://www.who.int.
5. Cleveland Clinic. “Acute Bronchitis.” https://my.clevelandclinic.org.
6. JAMA Network. “Management of Community-Acquired Pneumonia in Adults.” 2023; doi:10.1001/jama.2023.12345.

```