Rates of contaminant identification are increasing, as newer methods of testing improve the identification of bacteria, even in small amounts. Central venous catheters are associated with higher rates of contamination than venipuncture. Bacteria may also be present in medical devices, such as central venous catheters. 18 For example, normal skin bacteria may be introduced when a single needle venipuncture is performed. Contamination occurs when bacteria from an outside source are introduced into a collected sample. When evaluating blood cultures, it is important to differentiate between bacteremia and contamination. Considerations for interpreting results for blood, respiratory, urine, skin and soft tissue, bone and joint, cerebral spinal fluid, and stool cultures are provided below. 17 Poor culture-collection technique may also increase the risk of contamination. Sites that are well known for contamination include sputum and nasal passages. Sites that are typically thought of as sterile include cerebral spinal fluid, blood, and pericardial fluid. Those colonized with bacteria increase the risk of contamination from normal flora and may lead to false results. 14 – 16Ĭultures may be obtained from sites that are either colonized with bacteria or sterile. If cultures are drawn post-antibiotic administration, there may be a decrease in the blood-culture yield, which can increase the cost and length of stay for the patient. 13 Obtaining cultures before antibiotic administration can assist clinicians in identifying the offending organism, allowing potential de-escalation through proper treatment. 12 In septic patients, the administration of appropriate antibiotics within one hour can reduce mortality. Surviving Sepsis Campaign guidelines recommend that antibiotics be administered within one hour of sepsis diagnosis and that cultures should not delay antibiotic administration for more than 45 minutes. Medical professionals should obtain cultures quickly to guide therapy, simultaneously taking into consideration the importance of prompt antibiotic administration. Throughout the article, we use the term antibiotic instead of antimicrobial, as we did not cover the testing of viruses or fungi. 9, 10 This paper covers the timing of cultures, common culture sites, interpreting the Gram stain, the role of rapid diagnostic tests, conventional antibiotic susceptibility testing, and automated testing. Furthermore, bacterial resistance may develop, which can lead to treatment failure. 6 – 9 Inappropriate use may lead to increased adverse effects, secondary infections, drug interactions, additional costs, prolonged lengths of stay, and hospital readmissions. 2 – 5 The inappropriate use of antibiotics has been reported to be as high as 50%, although estimates can vary by institution and how “appropriate” is defined. 1 In hospital settings, studies suggest that approximately 50% of patients receive at least one antibiotic during their inpatient stay, 30% of which includes broad-spectrum antibiotics. This means that pharmacists in a variety of other positions must take on these roles in order to improve appropriate antibiotic prescribing. Currently, there is a shortage of pharmacists trained in infectious diseases to fill antimicrobial stewardship positions across the United States.
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