Community-acquired pathogens

There is a large reservoir of NoV in the commimity, as evidenced by surveys of community acquired and sporadic cases of gastroenteritis (Buesa et ah, 2002 Haustein et ah, 2009 Karsten et ah, 2009 Lindell et ah, 2005). Syndromic surveillance of vomiting reports also indicates that the presence of NoV infections is constantly fluctuating in different areas (Cooper et ah, 2008). This widespread reservoir means that NoVs are continually introduced into hospital settings where they can spread rapidly despite efforts to interrupt transmission (Cunliffe et al., 2010 Koopmans, 2009 Sommer et ah, 2009). Preventing the introduction of this widespread pathogen is nearly impossible (Koopmans, 2009 Yee et ah, 2007). 

Recognizing the presumed site of infection and most common pathogens associated with the infectious source should guide antimicrobial choice, dose, and route of administration. For example, community-acquired pneumonia is caused most commonly by S. pneumoniae, E. coli is the primary cause of uncomplicated UTIs, and staphylococci and streptococci are implicated most frequently in skin and skin-structure infections (e.g., cellulitis). 

List the common pathogens that cause community-acquired pneumonia, aspiration pneumonia, ventilator-associated pneumonia (early versus late onset), and health care-associated pneumonia. 

Streptococcus pneumoniae is the most common bacterial pathogen associated with community-acquired pneumonia. 

Community-acquired methicillin-resistant S. aureus (CA-MRSA) is becoming an increasingly common pathogen in cellulitis. CA-MRSA can be distinguished from health care-associated MRSA (HA-MRSA) by its genetic dissimilarity, host population, drug susceptibility patterns, and toxin production. 

Community-acquired pneumonia Health care-associated, ventilator-asociated, or nosocomial pneumonia (Early onset no risk factors for MDR pathogens) Third-generation cephalosporin plus a macrolide or doxycycline Third-generation cephalosporin OR Fluoroquinolone OR Ampicillin-sulbactam OR Ertapenem... 

Methicillin-resistant Staphylococcus aureus (MRSA) is a common hospital-acquired pathogen and is also increasing in the community. MRSA has presented a problem in the past because it required treatment with vancomycin. Community-acquired MRSA presents a major therapeutic challenge. MRSA can cause pneumonia, cellulitis, and other infections. Clinicians should be aware of the rate of hospital and community MRSA in your geographic area. New treatment options are available for MRSA. They include linezolid, tigecycline, and daptomycin. Prospective clinical trials have not demonstrated benefits of these agents over vancomycin.36-37... 

The vast majority of pneumonia cases acquired in the community by otherwise healthy adults are due to S. pneumoniae (pneumococcus) (up to 75% of all acute bacterial pneumonias in the United States). Other common bacterial causes include M. pneumoniae, Legionella, and C. pneumoniae, which are referred to as atypical pathogens. Community-acquired... 

For infections frequently encountered outside hospitals, e.g. uncomplicated urinary tract infection in young women, surveillance of resistance data of the most likely pathogens Escherichia coli) allows physicians to prescribe empiric therapy without performing cultures in the individual patient. However, in severely ill hospitalised patients, it is necessary to take samples for culture before starting empiric therapy. Microscopy of the Gram stained smear can help fine-tune empiric therapy at an early stage. Whether the infection is community-acquired or hospital-acquired, and whether the patient has been exposed to previous antimicrobial therapy should also be taken into account when choosing empiric therapy. 

Nafcillin, oxacillin, cloxacillin, and dicloxacillin are more resistant to bacterial (3-lactamases than is penicillin G. Consequently, these antibiotics are effective against streptococci and most community-acquired penicillinase-producing staphylococci. Methicillin, which is no longer marketed in the United States, is another penicillinase-resistant antibiotic similar to nafcillin and oxacillin. For historical reasons, staphylococci resistant to oxacillin or nafcillin are labeled methicillin resistant. Many hospitals are reservoirs for MRSA and methi-cillin-resistant Staphylococcus epidermidis (MRSE). These nosocomial pathogens are resistant in vitro to all (3-lactam antibiotics. 

Finally, there are many clinical entities, such as certain episodes of community-acquired pneumonia, in which it is difficult to identify a specific pathogen. In such cases, a clinical response to empiric therapy may be an important clue to the likely pathogen. 

Due to its powerful specific activity against commonly isolated community-acquired respiratory tract pathogens [33,149-158], including penicillin-sensitive and -resistant Streptococcus pneumoniae, methicillin-sensitive Staphylococcus aureus, Haemophilus spp., Moraxella catarrhalis and atypical pathogens such as Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella pneumophila and Klebsiella pneumoniae and anaerobic bacteria [159-162], moxifloxacin was developed as a respiratory tract anti-infective [163-168]. 

What are the important pathogens and appropriate treatment options for severe community-acquired pneumonia ... 

Studies of community-acquired pneumonia in the UK indicate that no organism is isolated in over 30% of cases (British Thoracic Society, 200f). Viruses are isolated in approximately f 3% of patients. Of the bacterial pathogens associated with community-acquired pneumonia, Streptococcus pneumoniae is the most important (isolated in almost 40% of cases), typically sensitive to benzylpeni-cillin and cephalosporin antibiotics. 

So-called atypical bacteria such as Chlamydia pneumoniae and Mycoplasma pneumoniae are the next most important group of community-acquired pneumonia pathogens, accounting for around one case in every eight in hospitalised patients. Atypical bacteria are not sensitive to beta-lactam antibiotics such as penicillins and cephalosporins and the treatment of choice is a macrolide such as erythromycin. 

Other less common pathogens include Staphylococcus aureus, Haemophilus influenzae and Gram-negative rods from the gastrointestinal tract. In severe community-acquired pneumonia, these pathogens must also be covered due to the high risk of mortality, hence the use of more broad-spectrum cephalosporins... 

The primary goal of therapy in community-acquired pneumonia is to reduce mortality. The secondary goal is to ensure prompt clinical response and symptom resolution with minimum risk of recurrence at an acceptable risk of treatment adverse effects. Other goals include reducing unnecessary disturbance of the patient s normal flora and the associated risk of superinfection with resistant pathogens such as Clostridium difficile. 

The patient s vital signs provide the most sensitive indicator of response to therapy and normalisation of heart rate, respiratory rate, oxygenation, blood pressure and temperature should be confirmed. Laboratory markers of infection such as CRP and WCC should be monitored to ensure normalisation. Failure to improve may indicate an incorrect diagnosis, a resistant pathogen, poor absorption of antibiotic, immunocompromise or local or distant complications of community-acquired pneumonia such as lung abscess. 

The treatment of community-acquired pneumonia may consist of humidified oxygen for hypoxemia, bronchodilators (albuterol) when bronchospasm is present, rehydration fluids, and chest physiotherapy for marked accumulation of retained respiratory secretions. Antibiotic regimens should be selected based on presumed causative pathogens and pulmonary distribution characteristics and should be adjusted to provide optimal activity against pathogens identified by culture (sputum or blood). 

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