Community-Acquired Pneumonia (CAP): Causes, Symptoms, and Treatment Guide

By  at July 26, 2025  , , ,  No comments


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Community-acquired pneumonia is one of the most common infectious diseases globally and a significant cause of hospitalization. Whether caused by bacteria, viruses, or fungi, it can quickly become severe if not treated early. Here's everything you need to know—from symptoms to treatment.


What Is Community-Acquired Pneumonia?


CAP is a lung infection that people get outside of hospitals or health care facilities. It causes the air sacs in the lungs to become inflamed and filled with fluid or pus, making it hard to breathe.


What Causes Community-Acquired Pneumonia?


Common Bacterial Causes



Atypical Bacteria


These won't show up on standard tests and have milder symptoms:



Viral Causes


Especially during flu season or outbreaks:


Fun fact: Pre-COVID, human rhinovirus was one of the most frequently isolated viruses in adults hospitalized with CAP.


Unusual and Rare CAP Pathogens



Who Is Most at Risk?


CAP can occur in anybody, but certain groups are more at risk:


  • Patients with COPD, asthma, or heart disease
  • Smokers and alcoholics
  • Adults over 65
  • Immunocompromised patients
  • People recovering from recent viral infections like the flu


Symptoms: How to Know If It's CAP


Classic Pneumonia Symptoms:


  • Fever and chills
  • Productive cough with yellow or green mucus
  • Chest pain that worsens on breathing
  • Shortness of breath
  • Crackling sounds in lungs


Symptoms of Atypical Pneumonia:


  • Low-grade fever
  • Dry cough
  • Headaches, ear pain
  • Muscle pains, diarrhea, or abdominal pain
  • Skin rash or confusion (especially in the elderly)


How Is Pneumonia Diagnosed?


Doctors may use the following tests:


Imaging:


  • Chest X-ray to confirm lung infiltrates
  • CT scan in complicated or immunocompromised patients


Lab Tests:


  • CBC with differential
  • CRP and procalcitonin (for inflammation)
  • Blood cultures and sputum tests
  • PCR testing for viruses or atypical bacteria
  • Legionella urinary antigen test

⚠️ Always test for influenza and COVID-19 during outbreaks or flu season.


When Does Pneumonia Require Hospitalization?


Use These Risk Scores:


Pneumonia Severity Index (PSI) – More accurate for determining hospitalization

CURB-65 – Quick score using:


  • Confusion
  • Urea level
  • Respiratory rate
  • Blood pressure
  • Age 65+


ICU Admission:


Requires mechanical ventilation or vasopressors

OR at least 3 minor symptoms such as:


  • Low oxygen levels
  • Confusion
  • Low white blood cell count


First-Line Treatment Options for CAP


Outpatient (No Comorbidities):



Outpatient (With Comorbidities):


Beta-lactam + macrolide

  (e.g., amoxicillin-clavulanate + azithromycin)

OR a respiratory fluoroquinolone

  (e.g., levofloxacin)


Inpatient Treatment:


Ceftriaxone + azithromycin

OR levofloxacin alone

Add vancomycin or linezolid if MRSA is suspected

Use piperacillin/tazobactam if Pseudomonas is likely


How Long Should Pneumonia Be Treated?


  • Uncomplicated CAP: 5 days
  • Complicated or severe cases (MRSA/Pseudomonas): 7+ days
  • Patients must be afebrile for 48–72 hours before stopping antibiotics


Pro Tips for Faster Recovery

  • Rest and hydrate
  • Use a humidifier to loosen breathing
  • Follow your asthma or COPD action plan
  • Get vaccinated against influenza and pneumococcal disease


Prevention of Community-Acquired Pneumonia


  • Get your flu vaccine annually
  • Stay up-to-date with COVID-19 vaccinations
  • Ask about the pneumococcal vaccine (especially if 65+ or high risk)
  • Avoid smoking
  • Wash your hands often


Final Takeaway


Community-acquired pneumonia can be treated—but early detection and quick care are essential. Whether you have a classic bacterial infection or a viral pneumonia like COVID-19, understanding your symptoms and risk factors guides the right treatment.

If you're having a persistent cough, shortness of breath, or chest pain—don't wait. Get a physician ASAP.


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