Definition

Community-acquired pneumonia (CAP) is defined as pneumonia in a patient who has not been hospitalized or has not resided in a long-term care facility (such as a nursing home) within the past 14 days.

It is an infection of the lower respiratory tract associated with signs or symptoms of acute infection and new CXR infiltrate.

Immunocompromised patients can get CAP, but treatment in these individuals is different and an expanded differential diagnosis should be considered.

http://www.hawaii.edu/medicine/pediatrics/pemxray/v4c03.html

These are PA and lateral films of RML pneumonia (arrows).Note the indistinct borders, air bronchograms, and silhouetting of the right heart border.

PA and Lateral films of RUL pneumonia

Diagnosis for Case of the Week - April 2, 2004

66 year old man s/p renal transplant with Shortness of Breathand Weight Loss

http://www.radiology.vcu.edu/programs/residents/quiz/Pulm_COTW/2004%2004%2002%20cotw.htm

Community-acquired pneumonia

Key Highlights

Common symptoms include :

o cough, o fever and chills, o fatigue, o dyspnea, o rigors and o pleuritic pain

Important historical factors to narrow the differential diagnosis are :

o recent respiratory infection, o exposure to respiratory illnesses,o immunocompromise,o smoking, o alcohol,o travel and o occupational riskso > 65 years old

OFTEN DIAGNOSIS AND TREATMENT CAN BE BASED SOLELY ON HISTORY AND PHYSICAL EXAM.

The most specific and sensitive test is CXR (PA and lateral).

Initial treatment is empirical with antibiotics.

Other Factors

o chills then fevero chest paino abdominal paino lung percussion dullnesso bronchial breath soundso tactile vocal fremitus

1st Tests To Order

o CXRo CBCo basic metabolic profileo oximetry or ABGo blood cultureo sputum culture o sputum Gram stain

Other Tests to Consider

o rapid urinary antigen testso thoracentesiso serologyo PCR o M pneumoniae cold agglutininso rapid viral diagnostic testso CT chesto Bronchoscopy

treatment

Acute

all patients

supportive care

outpatients

previously healthy and drug-resistance unlikely macrolide or tetracycline therapy comorbidities or risk factors for drug-resistant S pneumoniae

infection fluoroquinolone or combination therapy

inpatients

non-ICU cases fluoroquinolone or combination therapy vancomycin or linezolid ICU cases (nonpseudomonal) combination therapy vancomycin or linezolid ICU cases (pseudomonal) combination therapy

COMPLICATIONS

ARDS

Pneumonia can be complicated by ARDS, which is a condition of noncardiogenic pulmonary edema and severe lung inflammation.

This complication is associated with a 30% to 50% mortality and is treated with low tidal volume plateau pressure limited mechanical ventilation.

EMPYEMA

Patients with pneumonia might have metastatic infections such as empyema. [21]

Treated with antibiotics and operative drainage.

ARTHRITIS

Patients with pneumonia might have metastatic infections such as septic arthritis.

MENINGITIS

Patients with pneumonia might have metastatic infections such as meningitis. [21]

Treated with antibiotics that are able to cross the blood-brain barrier.

INFECTIVE ENDOCARDITIS

Patients with pneumonia might have metastatic infections such as endocarditis. [22]

Treated with antibiotics but may require higher doses and longer durations than for pneumonia alone.

PERICARDITIS

Patients with pneumonia might have metastatic infections such as pericarditis. [21]

Treated with antibiotics but may also require drainage.

Patients with pneumonia might have metastatic infections such as peritonitis. [21]

Treated with antibiotics.

Prognosis

Although prognosis is generally good for patients treated with the appropriate antibiotics, roughly only 80% of patients treated with antibiotics have a resolution of clinical signs and symptoms. A meta-analysis of 127 study cohorts revealed a mortality of nearly 14%. The range is from about 5% for hospitalized and ambulatory patients to over 30% for patients in intensive care. Factors associated with increased risk of mortality are: male sex, pleuritic chest pain, hypothermia, systolic hypotension, tachypnea, diabetes mellitus, neoplastic disease, neurologic disease, bacteremia, leukopenia and multilobar radiographic pulmonary infiltrate.

Monitoring

Monitoring parameters for CAP management should include aspects from both antimicrobial therapy and the disease state. Patients need to be educated on potential adverse reactions to chosen antibiotics and appropriate actions to be taken if these occur. For example, patients should be counseled on the signs and symptoms of severe allergic reactions and should be provided with emergency contact information in case of drug side effects. Patients should also be closely monitored either in person or by telephone for signs and symptoms of disease resolution or for the worsening of disease.

Important parameters include vital signs, symptoms, and CBC and oxygen saturation. Although there is a lag time between improving clinical response and clearing of the CXR, a repeated CXR 4 to 6 weeks after treatment may be used to ensure the condition has not got worse.

Patient Instructions

The importance of adherence to medication should be emphasized, even if the patient is feeling better. Patients should be instructed to call the office if their symptoms do not improve within 72 hours.

Patient should be instructed to increase water intake to at least eight 8 to 12-oz glasses per day, unless otherwise contraindicated. If a patient is a smoker, the importance of smoking cessation during this illness should be stressed. Patient should be explained how smoking impairs natural mechanisms to eliminate pathogens and debris.

To control systemic symptoms of pneumonia, aspirin or acetaminophen is recommended (aspirin should not be used in pediatric patients). Patient should be advised to avoid cough suppressants.

Patients should be advised that fatigue is common during the acute phase and that more rest than usual may be necessary. The patient can increase activity as tolerated after the acute phase.

Primary Prevention

CDC guidelines recommend pneumococcal polysaccharide vaccine should be administered to: [12]

Persons aged 65 years or greater Immunocompetent persons aged 2 years or greater who are

at increased risk for illness and death associated with pneumococcal disease because of chronic illness

Persons aged 2 years or greater with functional or anatomic asplenia

Persons aged 2 years or greater living in environments in which the risk for disease is high

Immunocompromised persons aged 2 years or greater who are at high risk for infection.

Protection lasts for over 6 years in most people, although the protective value may be lost at a faster rate in elderly people than in younger adults. Anyone at risk of serious pneumonia should be revaccinated 6 years after the first dose.

Secondary Prevention

Pneumococcal vaccine helps to prevent CAP

Pneumonia: there is poor-quality evidence that vaccination with pneumococcal vaccine may be no more effective than no vaccination at reducing the rates of acquiring definitive pneumococcal pneumonia in immunocompetent adults.

Evidence Level C

Poor quality observational (cohort) studies or methodologically flawed randomized controlled trials (RCTs) of < 200 participants

Emerging Therapies

TelithromycinThis new ketolide antibiotic is particularly active against resistant S pneumoniae strains. Telithromycin is indicated for mild-to-moderate CAP. However, the most recent ATS/IDSA guidelines comment that additional safety data is required before making specific recommendations for its use.

Diagnostic Criteria

Criteria for severe community-acquired pneumonia

Minor criteria:

Respiratory rate 30 breaths/minute or greater PaO2/FiO2 ratio 250 or less Multilobar infiltrates Confusion/disorientation Uremia (BUN ≥20 mg/dL) Leukopenia (WBC <4000 cells/mm^3) Thrombocytopenia (platelet count <100,000 cells/mm^3) Hypothermia (core temperature <96.8ºF [36ºC]) Hypotension, requiring aggressive fluid resuscitation

Major criteria:

Invasive mechanical ventilation Septic shock with need for vasopressors

ICU admission is recommended for patients with major criteria or 3 of the minor criteria.

Etiology

Streptococcus pneumoniae (also known as pneumococcus) is the most common cause of CAP.

CAP can also be caused by Haemophilus influenzae, Staphylococcusaureus, Moraxella catarrhalis, Klebsiella pneumoniae and other gram-negative bacilli.

Atypical microorganisms and respiratory viruses can also cause CAP. A 1996 prospective study identified the prevalence of various pathogens in 346 consecutive patients with CAP. Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella species accounted for 29%, 18% and 16% of cases, respectively.

Many viruses associated with CAP follow a seasonal pattern, including influenza virus, respiratory syncytial virus (RSV) and parainfluenza virus. Other viruses that can cause CAP in adults include adenovirus and hantavirus. For infants and young children, RSV is the most common cause of lower respiratory tract infections, with an estimated 25% of children hospitalized with pneumonia having RSV as the causative etiology.

Pathophysiology

Most of the infectious agents that cause CAP are aspirated into the lung. CAP that results from aspiration of oropharyngeal contents is the only form of CAP with multiple pathogens. Among older patients, microaspiration of oropharyngeal secretions is common and is more prevalent among patients with comorbidities and those taking medications that cause sedation.

An infection usually occurs when one component of the defense mechanism is not functioning properly. This results in microbial colonization of the upper respiratory tract. Microbes can enter and invade the lower respiratory tract by many methods and 6 mechanisms have been identified in the pathogenesis of pneumonia in immunocompetent adults:

Inhalation of infectious particles Aspiration of oropharyngeal or gastric contents Hematogenous deposition of bacteria in the lung Invasion from infection in contiguous structures Direct inoculation Reactivation.

Certain pre-existing conditions such as cystic fibrosis, COPD, corticosteroid use, immunodeficiency, stroke, drug and alcohol use, and pulmonary edema can hinder the ability of the host defense system to expel the possible pathogens that can predispose an individual to acquiring CAP.

Bacterial pathogenesis depends on the virulence and number of organisms aspirated. For encapsulated organisms, such as S pneumoniae, the presence of different capsular polysaccharides, which prevent the host serum bactericidal activity (antibodies and complement), and opsonic activity of polymorphonuclear leukocytes and macrophages may contribute to the pathogenesis and poor outcomes.

Once CAP is established, host humoral and cellular responses and early appropriate antimicrobial therapy are critical for containing the infection, preventing complications and improving outcome. Unfortunately, the rapid emergence of antibiotic resistance and immune deficiency has complicated treatment decisions.