Antimicrobics and Infectious Diseases Newsletter最新文献

Legionellosis is a respiratory tract infection with considerable morbidity and mortality that is being recognized more commonly as an important cause of community-acquired pneumonia as well as nosocomial pneumonia. As with all severe respiratory infections, an aggressive diagnostic approach is warranted for legionellosis. Clearly the most rapid diagnostic measures available should be employed in the diagnosis of these infections. However, rapidity is of no value with tests that are low in specificity and may provide ambiguous results. The standards in Legionella diagnosis are culture, DFA, and urinary antigen tests. The methods have been improved, but the principals have remained the same for the past two decades. Culture and antigen testing are highly specific, while DFA and urine antigen testing provide rapid results. Newer rapid tests emploring genetic detection are being developed, and will be increasingly incorporated by clinical microbiologists. Therapy, however, should not be dictated by the results of the diagnostic efforts as a delay in instituting appropriate therapy for legionellosis significantly increases the morbidity and mortality of this disease. Accordingly, empirical therapy for Legionella spp. should be included in the treatment of severe community-acquired pneumonia. Although intravenous erythromycin has historically been the drug of choice, newer macrolides such as azithromycin as well as fluoroquinolones have superior in vitro activity, greater intracellular and pulmonary tissue penetration, and are available in intravenous form. Parenteral therapy should be given until there is a clear clinical response. Rifampin is also highly active against Legionella spp. and may be combined with a newer macrolide or a fluoroquinolone in cases of severe illness. Therapy can be switched to oral dosing after a clinical response and should be continued for three weeks in immunocompromised patients, two weeks in others.

Appropriate early antimicrobial therapy of patients with serious infections caused by S. aureus is well recognized as an important factor for a favorable outcome. The fact that MRSA strains often are multi-resistant leaves only few antibiotics available for the therapy of MRSA infections. As a consequence, clinicians in many countries resort to the use of glycopeptides to broadly cover the patient for a possible MRSA infection until the results of cultures and susceptibility testing are available. Such use of glycopeptides clearly increases the selective pressure for vancomycin resistance, an issue which is of great concern in view of the increasing problem with vancomycin-resistant enterococci. Moreover, there is an additional risk that the overuse of vancomycin may lead to the development of vancomycin-resistant stains of MRSA, a situation for which no treatment would be available! Finally, therapy with glycopeptides results in higher cost as compared to ß-lactamase stable penicillins due to the higher cost of the drug as well as higher associated costs of therapy such as vancomycin levels. Rapid/accurate detection of MRS A is important in order to decrease the use of glycopeptide antibiotics. Furthermore, rapid and accurate detection increases the possibilities of reducing or even controlling the spread of MRSA. DNAbased rapid assays have been developed and should be available commercially soon. At present, these rapid assays are also being evaluated against methicillin resistance in coagulase negative staphylococci (CNST). Such resistance is also encoded by the mecA gene. CNST infections are increasing, especially in immunocompromised patients with methicillin resistance being very common in these strains. The existing phenotypic susceptibility methods detection of methicillin resistance is so unreliable when testing CNST that many clinicians choose to treat with glycopeptide antibiotics regardless of the test results.