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Title: Outcomes of Staphylococcus aureus bacteremia
Keywords: Staphylococcus aureus, bacteremia, MRSA, Infectious Disease consultation, Spa type, endocarditis
Issue Date: 18-Jul-2009
Citation: PRABHA PARTHASARATHY (2009-07-18). Outcomes of Staphylococcus aureus bacteremia. ScholarBank@NUS Repository.
Abstract: Staphylococcus aureus bacteremia (SAB), a leading cause of community and healthcare associated bacteremias is well known for complications such as a high mortality rate, endocarditis, metastatic infections and recurrence. The epidemiology of SAB is different worldwide due to differing rate of Methicillin Resistant Staphylococcus aureus (MRSA) and different comorbidities in the population. While most of the reports are available from the Western World, there is scant information in the Asian context. Hence, we decided to undertake this study at the National University Hospital with the main aim to define the outcomes of SAB. In addition, we evaluated the effect of an Infectious Disease (ID) consultation in a randomized trial and performed genotyping by the Staphylococcus Protein A (Spa) Typing method on a subset of strains. We recruited 300 consecutive patients with SAB making this one of the largest cohorts of SAB patients to be studied in Asia. . The SAB and MRSA bacteremia rate was 3.42 and 1.44 per 1000 discharges or deaths. The epidemiology was characterized by a high percentage of MRSA (42%) and underlying comorbidities(88.4%). The mortality, infective endocarditis and recurrence rate was 29, 14.5% and 9.9% of all SAB cases respectively. On a multivariate logistic regression, MRSA infection, elderly age, malignancies, history of skin disease, and a higher APACHE score were associated with mortality; persistent bacteremia and IV drug use was associated with metastatic infections. In MRSA patients, metastatic seeding was commonly isolated bony infection and infective endocarditis. 21% of the MRSA strains had a vancomycin MIC of 2 or higher. The higher MIC was associated with bony metastatic infection and persistent bacteremia. An ID consultation when evaluated in a randomized trial was associated with a better standard of care; however, outcomes of mortality and recurrence were comparable. The results are still preliminary and further evaluation of other outcome parameters is needed before drawing conclusions. Genotyping of MRSA revealed 9 Spa types, 89% of which belonged to t032 (ST22, E-MRSA15, 21%) and t037 (ST 239-241, 68%). There was only one case of C-MRSA. Spa type t032 was associated with more endocarditis and pneumonia, however, mortality and recurrence was similar to t037. In conclusion, the epidemiology and outcomes at our center were similar to those reported from the Western World such as USA or UK. The high proportion of infections due to MRSA warrants an intensification of the current infection control practices. There is a need for use of scoring systems such as APACHE II and Charlson score to adjust for underlying comorbidities. SAB patients including MRSA cases are prone for metastatic infections; hence a high degree of suspicion and imaging, in particular Transesophageal echocardiography is warranted. Amidst concerns of rising rates of the emergent E-MRSA 15 (t032), the outcome of bacteremia due to this clone was not different from others. Spa typing is a convenient and a good screening molecular typing method to draw relevant epidemiological conclusions.
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