Two Simple Ways to Improve Diagnosis of Infectious Diseases

Valeria Fabre, MD


March 15, 2018

Editorial Collaboration

Medscape &

Bloodstream Infections and Clostridium difficile

Two recent studies published in Infection Control and Hospital Epidemiology draw attention to two simple clinical practices that can have a great impact on diagnosis and management of C difficile (laxative use)[1] and bloodstream infections (blood sample volume for blood cultures).[2]

The most recent National and State Healthcare-Associated Infections (HAIs) Progress Report shows that there has been significant reduction in central line-associated bloodstream infection (CLABSI) and a milder improvement in hospital-onset C difficile infection (CDI) in acute care hospitals in the United States in recent years. However, when we look at the state level, we see a similar number of states that have performed better and worse for both CLABSI and CDI, emphasizing the need for continuing to work on prevention strategies to tackle both of these HAIs.

Laxatives and Diarrhea

Ahmad and colleagues[1] conducted a retrospective observational study of 211 patients admitted to a US teaching community hospital who tested positive for C difficile and received laxatives before the testing. Of note, almost 40% (82/211) of the patients had received one or more laxatives within 7 days before C difficile testing, and 18% (15/82) continued to receive laxatives for >24 hours after a positive C difficile test.

Diarrhea resolved within 48 hours in 41% (12/29) of patients who had received laxatives within 24 hours before testing, including patients who did not receive C difficile treatment, suggesting that the cause of diarrhea in many patients undergoing C difficile testing is noninfectious.

This study not only shows that a large proportion of C difficile testing is inappropriate due to laxative use at the time of C difficile testing but also shows inappropriate laxative use in C difficile-positive patients. Several reports have demonstrated reductions in inappropriate C difficile testing by restricting orders in the electronic health record or rejecting inadequate specimens, although there has been less attention to laxative use after C difficile tests come back positive, which may influence CDI treatment.

More Blood in the Culture Vial

Another article reports on clinical variables that influence blood culture volume recovery. Obtaining an adequate sample volume for blood cultures is important in the detection of bacteremia because underfilling blood culture bottles is associated with increased levels of blood contamination, increased time to positivity, and reduced sensitivity for detecting bloodstream infections.

Jones and colleagues[2] conducted a retrospective study of 568 blood cultures from 128 unique adult patients collected during a 6-day observation period at a tertiary care center in the United States. Blood volume was estimated by weight after incubation. The study revealed that only a minority of bottles contained the recommended 8- to 10-mL blood sample volume. Only 25% of bottles collected from central venous catheters and 10% of bottles collected from peripheral venipuncture had sufficient blood sample volume. Furthermore, insufficient blood volume was more common in samples collected from peripheral venipuncture than in those obtained from central catheters (average, 2.5 mL less blood). The study was not powered to look at the effect of draw location on culture positivity, but it raises awareness of an important aspect of bacteremia detection that must be monitored to optimize blood culture yield and contamination rates.


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