A group of researchers collected demographic and clinical data from multiple hospitals across the nation to determine epidemiological features of nosocomial bloodstream infections. In this study, a nosocomial bloodstream infection was diagnosed if blood cultures drawn 48 hours after admission yielded a pathogenic organism. Analysis of the data collected over several decades shows that staphylococci are increasingly responsible for the identified cases. An increased use of which of the following is most likely the underlying cause of the observed trend?

Question

A group of researchers collected demographic and clinical data from multiple hospitals across the nation to determine epidemiological features of nosocomial bloodstream infections.  In this study, a nosocomial bloodstream infection was diagnosed if blood cultures drawn 48 hours after admission yielded a pathogenic organism.  Analysis of the data collected over several decades shows that staphylococci are increasingly responsible for the identified cases.  An increased use of which of the following is most likely the underlying cause of the observed trend?

Quizplus · Accepted Answer

11ec160b_3813_dd5e_9249_ef93b3d5e251_MD0001_00 Approximately 250,000 nosocomial bloodstream infections (BSIs) are estimated to occur in the United States each year. Prior to the 1980s, the leading cause was gram-negative aerobic organisms such as Escherichia coli that spread from primary infections in the genitourinary or gastrointestinal tract. However, the increasing use of intravascular catheters, which provide a portal of entry for skin flora to reach the bloodstream, has led to a shift in the underlying microbiology of BSI; most cases are now caused by skin commensals such as coagulase-negative staphylococci and Staphylococcus aureus. BSI is most common in those who have long-term (>12 days) central venous access as this provides sufficient time for skin flora to colonize the internal/external lumen of the catheter, to replicate within a biofilm of host (fibrin) and bacterial (glycoprotein) components, and to subsequently spread to the bloodstream. BSI should be suspected when a patient with an intravascular catheter develops new-onset fever or bacteremia. (Choice A) Although S aureus is a leading cause of infective endocarditis in patients with artificial heart valves, bacteremia is much more commonly caused by intravascular devices. (Choice B) The increased use of broad-spectrum antibiotics is associated with the development of drug-resistant organisms, including methicillin-resistant S aureus (MRSA). Although MRSA is a common cause of skin abscess and necrotizing pneumonia, the majority of S aureus bacteremia is caused by intravascular catheters. (Choice C) Injection drug use is a major risk factor for S aureus abscess, bacteremia, and infective endocarditis. However, injection drug use causes far fewer BSIs than intravenous catheters. (Choice D) Immunosuppression increases the risk of BSI due to reduced immunosurveillance. However, BSI is far more often due to the use of intravascular catheters. (Choice E) Indwelling urinary catheters increase the risk of urinary infection with subsequent hematogenous spread of the organism. However, most cases are caused by gram-negative enteric organisms such as E coli. Educational objective: Nosocomial bloodstream infections are usually associated with intravascular catheters, which allow skin commensals such as Staphylococcus aureus and coagulase-negative staphylococci to enter the bloodstream.

A Group of Researchers Collected Demographic and Clinical Data from Multiple