Community acquired pneumonia resident survival guide

# Overview
A lower respiratory tract infection in a previously normal individual acquired through normal social contact rather than contracting it in a hospital. Community-acquired pneumonia (CAP) is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs. CAP is a common illness and can affect people of all ages. It often causes problems like dyspnea, fever, chest pain, and cough. CAP causes fluid accumulation in the alveoli leading to poor gas exchange. CAP is common worldwide and is a leading cause of illness and death. Causes of CAP include bacteria, viruses, fungi, and parasites. CAP can be diagnosed by history and a physical examination alone, though x-rays, sputum examinations, and other diagnostic tests are often used. As CAP is often bacterial, the primary empiric treatment consists of wide-spectrum antibiotics. Some forms of CAP, such as pneumococcal pneumonia may be prevented by vaccination.

# Causes

## Life Threatening Causes
Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.  Complications of community acquired pneumonia, such as pleural effusion, lung abscess, bacteremia and septicemia are life-threatening conditions and must be treated as such irrespective of the causes.

## Common Causes
- Typical Bacteria
- Streptococcus pneumoniae
- Haemophilus influenzae
- Escherichia coli
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
- Atypical Bacteria
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Legionella pneumophila
- Viruses
- Influenza
- Parainfluenza
- Respiratory syncytial virus (RSV)
- Metapneumovirus
- Adenovirus
- Outpatient
- Streptococcus pneumoniae
- Mycoplasma pneumoniae
- Haemophilus influenzae
- Chlamydophila pneumoniae
- Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
- Inpatient (non-ICU)
- Streptococcus pneumoniae
- Mycoplasma pneumoniae
- Chlamydophila pneumoniae
- Haemophilus influenzae
- Legionella
- Aspiration
- Influenza A and B, adenovirus, respiratory syncytial virus, parainfluenza
- Yersinia enterocolitica
- Inpatient (ICU)
- Streptococcus pneumoniae
- Staphylococcus aureus
- Legionella
- Gram-negative bacilli
- Haemophilus influenzae
- Acinetobacter baumannii

# Management
Shown below is an algorithm depicting the management of community acquired pneumonia according to the Infectious Diseases Society of America (IDSA) and Thoracic Society Consensus Guidelines on the Management of Community Acquired Pneumonia in Adults.

## Empiric Antibiotics

## Empiric Antiviral

## Considerations in Severe Cases

## Pneumonia Severity Index

## CURB-65

# Do's
- If the patient presented to the emergency department, administer the fist dose of antibitoic therapy as soon as possible, preferably within 6 hours of presentation.
- Among patients admitted to the hospital, switch from IV to PO antibiotics as soon as the patient is hemodynamically stable with clinical improvement and ability to tolerate oral intake.  When the patient is switched to PO antibiotics, the patient can be discharged on PO home medications.
- The duration of antibiotics is at least 5 days; antibiotic treatment are not discontinued until  the patient is afebrile for 48-72 hours and with not more than one sign of instability.
- Use fibre-optic bronchoscopy in immunocompromised individuals to detect less common organisms, obtain a tissue biopsy, and identify anatomic lesions if any.
- Treat influenza A with oseltamivir or zonamivir only if time from onset of symptoms < 48 hours.
- Consider a F/U chest X-ray at 6 weeks to rule out an underlying lung malignancy.

# Dont's
- Inadvertently use of antibiotic for patients without community-acquired pneumonia who require treatment within 4 hours may increase the risk of Clostridium difficile colitis.  Hence, use antibiotics judiciously.