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Community-Acquired Pneumonia: Diagnostic and treatment Perspectives

Asthma, Age related illnesses, General | November 22, 2014 | Author: The Super Pharmacist

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Community-Acquired Pneumonia: Diagnostic and treatment Perspectives

Community-acquired pneumonia (CAP) is one of the leading causes of death worldwide and is associated with a high economic burden. Although the mortality rate in patients with CAP was dramatically reduced by the introduction of antibiotics in the 1950s, it has not decreased greatly since that time.

Pneumonia is an inflammation or infection of the lungs that causes them to function abnormally.

Community-acquired pneumonia (CAP) is defined as pneumonia not acquired in a hospital or a long-term care facility. 

Symptoms of Pneumonia

Symptoms of PneumoniaCommon clinical symptoms of pneumonia include cough, fever, chills, fatigue, dyspnea (shortness of breath), rigors (shaking or exaggerated shivering which can occur with a high fever), and pleuritic chest pain (resulting from 'pleurisy,' an inflammation of the pleura or the lining of the lungs). Depending on the organism responsible for the infection, a patient’s cough may be persistent and dry,
or it may produce sputum.

Other presentations may include headache and myalgia (muscle aches). Certain pneumonias, such as legionella, may also produce gastrointestinal symptoms.

Causes of Community-Acquired Pneumonia

Community-acquired pneumonia is usually acquired via inhalation or aspiration of pathogenic organisms into the lungs. Pneumonia can be classified as typical or atypical, although the clinical presentations are often similar.

Typical pneumonia is usually caused by bacteria such as Streptococcus pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis. Streptococcus pneumoniae remains the most common agent responsible for CAP. 

Atypical pneumonia is caused by Chlamydophila (Chlamydiapsittaci (psittacosis),  Francisella tularensis (tularemia), Coxiella burnetii (Q fever), Legionella species, M pneumoniae, and Chlamydophila  (Chlamydia)  pneumoniae

Importantly, bacteria such as Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa are not common causes of CAP in otherwise healthy hosts. Staphylococcus aureus may cause CAP in individuals with influenza (e.g. human seasonal influenza and H1N1 [swine] influenza). Klebsiella pneumoniae  CAP occurs primarily in individuals with chronic alcoholism.

Causes of Community-Acquired PneumoniaThe common pathogens causing CAP are reported to be very similar in many parts of the world, including the United States, Europe, Latin America, Asia-Pacific and sub-Saharan Africa, with a few exceptions. 
In most areas, the most common organism is Streptococcus pneumoniae (pneumococcus) and this holds true in cases treated in the outpatient, inpatient, or even the intensive care setting.

Other common pathogens are the atypical pathogens. Atypical pathogens include Mycoplasma pneumoniae, Legionella and Chlamydophila species. 

Guidelines for treatment of CAP

The Australian Government has produced guidelines that recommend (empiric) treatment for CAP based on pneumonia severity. The most recent (2011) Australasian Therapeutic Guidelines recommends the use of either CORB or SMART-COP instead of the PSI (or CURB-65) for scoring pneumonia severity. Therapy is predicated on the severity of illness.

Mild Community-acquired pneumonia. Usually treatment is conducted as an outpatient. Amoxicillin orally is recommended, while doxycycline or clarithromycin are recommended for atypical organisms such as M. pneumoniae.

Moderate Community-acquired pneumonia. For moderate CAP, the Australian guidelines recommend the use of benzylpenicillin intravenously plus either doxycycline or clarithromycin orally.

Severe Community-acquired pneumonia. In patients with severe CAP, the Australian guidelines recommend the use of intravenous benzylpenicillin with gentamicin and azithromycin intravenous/orally. If there is a documented penicillin allergy, intravenous ceftriaxone plus azithromycin is recommended. Adherence to empiric antibiotic guidelines for the management of patients with CAP has been demonstrated to reduce mortality and morbidity, shorten the length of hospital admission, and decrease healthcare costs. However, there is substantial evidence to suggest that national guidelines for management of patients with CAP in Australia are often poorly adhered to in clinical practice.

Guidelines for treatment¬†of CAPAccording to a 2014 study conducted at the School of Medicine, Deakin University, Victoria, Australia, authors found that greater than 50% of patients with CAP in their institution received broad-spectrum antibiotics, such as a third-generation cephalosporin (ceftriaxone) as either monotherapy or in combination with another antibiotic.

Similar findings have been reported in other Australian studies. 

While cautioning against the dangers of widespread use of third-generation cephalosporins, authors of this study indicate that, despite the global increase in pneumococcal resistance and high rates of penicillin resistance measured internationally, rates of penicillin resistance remain low in Australia. Significantly, they quote public health reports which show that, in 2001, 12% of all invasive pneumococcal isolates were penicillin resistant, while in 2006, 10.6% of invasive pneumococcal isolates were resistant or of intermediate susceptibility to penicillin, a figure which is lower than the resistance rates in 2005. These authors qualify their recommendations by acknowledging geographic variation in susceptibility to penicillin within Australia, but conclude that benzylpenicillin remains a reasonable first-line treatment for patients with CAP.

U.S. Guidelines for CAP?

Two of the most widely referenced guidelines for CAP are those of the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS). In response to confusion regarding differences between their respective guidelines, the IDSA and the ATS convened a joint committee to develop a unified CAP guideline document. Enthusiasm for developing these guidelines derives, in large part, from evidence that previous CAP guidelines have led to improvement in clinically relevant outcomes.

Routine evaluation

A chest X-ray is required for the routine evaluation of patients who are likely to have pneumonia, to establish the diagnosis and to aid in differentiating CAP from other common causes of cough and fever, such as acute bronchitis.

Recommendations for further diagnostic testing remain controversial. The overall low yield and infrequent positive impact on clinical care argue against the routine use of common tests, such as blood and sputum cultures. Conversely, these cultures may have a major impact on the care of an individual patient and are important for epidemiologic reasons, including the antibiotic susceptibility patterns used to develop treatment guidelines.

A list of clinical indications for more extensive diagnostic testing has, therefore, been developed, primarily on the basis of 2 criteria: (1) when the result is likely to change individual antibiotic management and (2) when the test is likely to have the highest yield. Routine diagnostic tests to identify an etiologic diagnosis are optional for outpatients with CAP.

Pre-treatment blood samples for culture and an expectorated sputum sample for stain and culture (in patients with a productive cough) should be obtained from hospitalised patients with the clinical indications listed above, but are optional for patients without these conditions. 

The most clear-cut indication for extensive diagnostic testing is in the critically ill CAP patient. Such patients should have blood drawn for culture and an endotracheal aspirate obtained if they are intubated. Urinary antigen tests for Legionella pneumophila and Streptococcus pneumoniae should be performed. 

Once the etiology of CAP has been identified on the basis of reliable microbiological methods, antimicrobial therapy should be directed at that pathogen.

Although recent research suggests that azithromycin may be associated with increased cardiovascular events, two studies have documented that in elderly patients hospitalized with community-acquired pneumonia, early survival benefits with azithromycin greatly exceeded the risk of nonfatal MI.

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