Community-acquired pneumonia (CAP) is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs (pneumonia).

Community-acquired pneumonia (CAP) is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs (pneumonia). Pneumonia is an infection of the lung parenchyma. CAP is a common illness and can affect people of all ages. Mortality and morbidity rates of CAP are highest in elderly patients.CAP is an important cause of mortality and morbidity worldwide. It often causes problems like difficulty in breathing, fever, chest pains, and a cough.

PathophysiologyCAP is usually acquired via inhalation or aspiration of pulmonary pathogenic organisms into a lung segment or lobe. Less commonly, CAP results from secondary bacteremia from a distant source, such as Escherichia coli urinary tract infection and/or bacteremia. CAP due to aspiration of oropharyngeal contents is the only form of CAP involving multiple pathogens.

PrevalenceDespite a broad armamentarium of antimicrobials available to treat the disease, pneumonia remains the seventh leading cause of death in the United States. In 2003, the age-adjusted death rate caused by influenza and pneumonia was 22.0 per 100,000 persons. Estimates of the incidence of community-acquired pneumonia range from four to five million cases per year, with about 25% requiring hospitalization.

Symptoms

problems breathing coughing that produces greenish or yellow sputum a high fever that may be accompanied with sweating, chills, and uncontrollable shaking sharp or stabbing chest pain rapid, shallow breathing that is often painful Less common symptoms include:the coughing up of blood (hemoptysis) headaches (including migraine headaches) loss of appetite excessive fatigue blueness of the skin (cyanosis) nausea vomiting diarrhea joint pain (arthralgia) muscle aches (myalgia) The manifestations of pneumonia, like those for many conditions, might not be typical in older people. They might instead experience:new or worsening confusion hypothermia falls* Additional symptoms for infants could include:being overly sleepy yellowing of the skin (jaundice) difficulties feeding[2]

The patient's history can help narrow the microbial differential diagnosis. The chest radiograph is the cornerstone of diagnosis. The sputum Gram stain and culture are controversial, but still useful for targeting antimicrobial therapy. Serologic testing is slow and therefore often not useful for real-time diagnosis. Molecular methods are playing an increasing role in identifying difficult to culture pathogens. The pneumonia severity index uses history, examination, chest radiograph, and initial laboratory test results to identify low-risk patients for outpatient treatment.

other include long-recognized pathogens such as Haemophilus influenzae, Mycoplasma pneumoniae, and influenza A, along with newer pathogens such as Legionella species and Chlamydophilia pneumoniae. Other common causes in the immunocompetent patient include Moraxella catarrhalis, Mycobacterium tuberculosis, and aspiration pneumonia.

The causative agent of community-acquired pneumonia remains unidentified in 30% to 50% of cases.

Previously seen mainly in extended-care facilities and acute care hospitals, strains of methicillin-resistant Staphylococcus aureus (MRSA) have recently emerged as prevalent pathogens in community settings

Mechanism Frequency

Inhalation of infectious particles Common

Aspiration of oropharyngeal or gastric contents Common

Hematogenous deposition Uncommon

Invasion from infection in contiguous structures Rare

Direct inoculation Less common

Re-activation

More commom in immunocompromised

patients

In 2001, the American Thoracic Society, drawing on work by the British and Canadian Thoracic Societies, established guidelines for the management of adults with CAP which divided individuals with CAP into four categories based upon common organisms encountered.

Healthy outpatients without risk factors This group, the largest, is composed of otherwise healthy patients without risk factors for DRSP, enteric Gram negative bacteria, Pseudomonas, or other less common causes of CAP.

The primary microoganisms in this group are viruses, atypical bacteria, penicillin sensitive Streptococcus pneumoniae, and Hemophilus influenzae.

Recommended management is with a macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.

Outpatients with underlying illness and/or risk factors This group does not require hospitalization; its members either have underlying health problems (such as emphysema or congestive heart failure) or is at risk for DRSP and/or enteric Gram negative bacteria.

Treatment is with a fluoroquinolone active against Streptococcus pneumoniae such as levofloxacin or a beta-lactam antibiotic such as cefpodoxime, cefuroxime, amoxicillin, or amoxicillin/clavulanate plus a macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.

DRSP:drug resistant streptococcus pneumonia

Hospitalized individuals not at risk for Pseudomonas This group requires hospitalization and administration of intravenous antibiotics.

Treatment is with either an intravenous fluoroquinolone active against Streptococcus pneumoniae such as levofloxacin or beta-lactam antibiotic such as cefotaxime, ceftriaxone, ampicillin/sulbactam, or high-dose ampicillin plus an intravenous macrolide antibiotic such as azithromycin or clarithromycin for seven to ten days.

Individuals requiring intensive care at risk for Pseudomonas aeruginosa require specific antibiotics targeting this difficult to eradicate bacteria

One possible regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/tazobactam plus an intravenous antipseudomonal fluoroquinolone such as levofloxacin.

Another recommended regimen is an intravenous antipseudomonal beta-lactam such as cefepime, imipenem, meropenem, or piperacillin/ tazobactam plus an intravenous aminoglycoside such as gentamicin or tobramycin plus either an intravenous macrolide such azithromycin or an intravenous nonpseudomonal fluoroquinolone such as ciprofloxacin.

Anthrax Suspected or proven inhalation anthrax

should be treated with ciprofloxacin or doxycycline .

Clinical experience has suggested that rifampin may be an important agent in empirical regimens.

Duration of Therapy Although few data specifically address the duration of therapy, many cases of pneumonia are adequately treated with 10 to 14 days of antibiotics. Longer courses may be required for certain organisms that cause tissue necrosis, (e.g., Legionella spp., S. aureus, Pseudomonas aeruginosa), organisms that live intracellularly (e.g., C. pneumoniae), or comorbidities that compromise local (COPD) or systemic (hematologic malignancy) immunity.

Oral and Switch Therapies The use of oral or switch therapies offers potential reductions in duration of stay, antibiotic administration costs, complications of venous access, and disruption of families and careers. Many antibiotics are well absorbed from the gastrointestinal tract, suggesting the possibility of effective, fully oral treatment. Because well-controlled, risk-stratified data comparing oral and intravenous therapies are few, appropriate patient populations and treatment settings for full-course oral therapy have yet to be fully defined. Better data exist for the use of IV to oral switch therapies for the stable patient who has good gastrointestinal and swallowing function and adequate social support