Community acquired Pneumonia - What should you know ?

Background - 

      Community-acquired pneumonia (CAP) is a common and potentially serious respiratory infection that affects individuals who have not been hospitalized or living in a long-term care facility within 14 days prior to the onset of symptoms. CAP can be caused by a variety of pathogens including bacteria, viruses, and fungi. In this article, we will discuss the epidemiology, etiology, pathophysiology, clinical features, diagnosis, and management of CAP.

Epidemiology-

       CAP is a significant cause of morbidity and mortality worldwide. It is estimated that approximately 4 million cases of CAP occur annually in the United States, resulting in over 1 million hospitalizations and 50,000 deaths. The incidence of CAP increases with age, with the highest rates observed among individuals over the age of 65. Other risk factors for CAP include chronic lung disease, heart disease, immunosuppression, and smoking.

Etiology-

                The etiology of CAP varies depending on the patient population, geographic location, and season. The most common bacterial pathogens responsible for CAP include Streptococcus pneumoniae, Haemophilus influenzae, and atypical bacteria such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila. Viral pathogens such as influenza virus, respiratory syncytial virus, and adenovirus are also common causes of CAP, particularly in children. Fungal pathogens such as Pneumocystis jirovecii and Histoplasma capsulatum may cause CAP in immunocompromised individuals.

Pathophysiology-

          CAP typically begins with the inhalation of a pathogen, which then colonizes the upper respiratory tract. If the host's immune defenses are compromised, the pathogen may spread to the lower respiratory tract and cause pneumonia. The pathophysiology of CAP involves an inflammatory response in the lungs, leading to alveolar damage, impaired gas exchange, and respiratory failure in severe cases.

Clinical Features-

     The clinical presentation of CAP can vary depending on the underlying pathogen, patient age, and comorbidities. Common symptoms include cough, fever, dyspnea, chest pain, and sputum production. Physical examination may reveal tachypnea, crackles on lung auscultation, and signs of respiratory distress. In severe cases, sepsis, shock, and acute respiratory distress syndrome (ARDS) may develop.

Diagnosis-

    The diagnosis of CAP is based on a combination of clinical features, laboratory tests, and imaging studies. Chest radiography is the most commonly used imaging modality to diagnose CAP, with typical findings including lobar or segmental consolidation, pleural effusions, and interstitial infiltrates.

    

    Blood cultures, sputum cultures, and respiratory viral panels may also be obtained to identify the underlying pathogen. In severe cases, arterial blood gas analysis and bronchoscopy with bronchoalveolar lavage may be necessary to confirm the diagnosis.

Management-

       The management of CAP depends on the severity of the illness and the underlying pathogen. Empirical antibiotic therapy should be initiated promptly for all patients with suspected CAP, with selection based on local resistance patterns and patient factors such as comorbidities and recent antibiotic use. Supportive care including oxygen therapy, bronchodilators, and fluid resuscitation should also be provided as needed. In severe cases, mechanical ventilation and vasopressor support may be necessary. Vaccination against S. pneumoniae and influenza have often proved helpful in decreasing the clinical severity of pneumonia in susceptible individuals. 

FAQs of CAP - 

a) What are the major causes of community acquired pnuemoniae ?  

   Streptococcus pneumoniae, Haemophilus influenzae,Moraxella catarrhalis, Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella species.

b) What is the most common treatment regimen of community acquired pneumoniae ? 

Depending on the local antibiotic policy, diagnostic parameters and patient's clinical condition 14 day regimen of Injection Ceftriaxone/Cefotaxime/Amoxicillin with or without addition of a macrolide like Azithromycin/Clarithromycin or Doxycline is considered as the treatment of choice. Iatroconazole can be considered if there is high degree suspicion of histoplasmosis or coccidioidomycosis. Treatment with Oseltamivir is considered for 5 days when respiratory secretions are Real Time RT-PCR positive for Influenza. 

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