Community-acquired pneumonia

Pneumonia is the 6th leading cause of death in USA, and the 1st cause of death by infectious diseases among american population. It is most commonly cause by bacteria (Streptococcus pneumoniae, Hemophillus influenzae, Mycoplasma pneumoniae, Legionella pneumophilia, Chlamidiae pneumoniae, other gram-positive (ie, Staphylococcus aureus (MSSA-MRSA) and gram-negative organisms (Pseudomonas aeruginosa, Klebsiella pneumoniae), etc. It can be also caused by viral agents such as Influenzae, para-Influenzae, RSV (respiratory syncitial virus), adenovirus, etc. Some fungi species(Pneumocystis jiroveci, Cryptococcus neoformans, Coccidiodes immitis, Histoplasma capsulatum, Aspergillus fumigatus) plays also an important role in the etiology of pneumonia, especially among immunocompromissed patients.
The most common clinical symptoms and signs of patients with pneumonia are cough (usually productive), dyspnea, tachypnea, pleuritic pain, fever or hypothermia, hypoxemia, etc. Based on the etiology, remarkable laboratory findings are increased or decreased white blood cell count, abnormal liver function test, electrolytes abnormalities, etc.
Chest radiography may vary from normal CXR to lobar/multilobar infiltrates to diffusse bilateral interstitial infiltrates. Pleural effussion is not an uncommon finding.
Basic workup for patients with community-acquiered pneumonia includes blood cultures, urine analysis, urine culture, respiratory secretions cultures, Legionella and Streptococcus pneumoniae urine antigens. Depending on the epidemiology, serum cryptococcal antigen, Histoplasma urine antigen, HIV test, respiratory cultures for acid-fast bacilli organisms (Nocardia species, Actinomyces species, atypical mycobacteria, Mycobacterium tuberculosis), may be appropriate.
It is also important to classified these patients using the CURB-65 criteria (C stands for confusion, U stands for azootemia (BUN >19), R stands for respiratory rate >30/min), B stands for hypotension (systolic BP <90 and/or diastolic BP <60), and 65 is the cutoff age).
Initial empiric antimicrobial therapy should be initiated within the first 4 hours of arrival to ER, and is based on a combination of a B-lactam antibiotic (ie, ceftriaxone or cefotaxime) plus a macrolide (ie, azithromycin, clarythromacin) or a quinolone (ie, moxifloxacin, levofloxacin). If no complications, therapy is continue for a total of 5-7 days (in patients with Streptococcus pneumoniae infection), and 14-21 days (in cases of atypical pneumonias, such as those caused by Legionella, Mycoplasma, Chlamidiae species).
Prevention is based on vaccines administration (Influenza and Streptococcus pneumoniae; for guidelines, please see IDSA guidelines for vaccine administration).