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Patients' Gut, Not Medical Professionals’ Dirty Hands, Causes Many Bloodstream Infections

Patients’ Bodies Most Common Source of Hospital-Acquired Bloodstream Infections

A hospital stay of longer than several days often leads to infections. Using new bioinformatics software, investigators from the Stanford University School of Medicine discovered the most common source of bloodstream infections stemmed from patients’ large intestines rather than germs from visitors or other patients.

More than 40 percent of immunocompromised patients—including some 23,000 annual recipients of bone-marrow transplants—develop bloodstream infections during hospital stays of two to six weeks.

The ability to trace infections to their actual origins, rather than simply administering broad-spectrum antibiotics, is a huge step toward addressing the risk factors that cause such infections, according to Ami Bhatt, MD, PhD, assistant professor of hematology and genetics.

In future, medical practitioners could quickly discover whether the pathogen causing the bloodstream infection came from a skin tear, leaked through the intestinal wall, or came from the surface of an inserted catheter or a hospital wall. This discovery would ensure that better informed steps were taken to eradicate the infection.

The scientists analyzed blood and stool samples from 30 patients who had incurred bloodstream infections after having bone-marrow transplant procedures at Stanford Hospital between early October 2015 and early June 2017. The goal was to determine whether the particular strain of pathogen isolated from a patient's blood also showed up in the stool specimen, collected before surgery.

As one bacterial species can consist of thousands or millions of different strains, analysis can prove difficult. Finding E. coli in a patient's blood and again in his stool does not necessarily mean they are the same strain, said Dr. Bhatt. But the researchers’ computational tool, StrainSifter, vastly sped up the process of analyzing the genomes of all the individual microbial strains in each patient’s stool to determine whether any of them precisely matched any of the multiple strains found in the patient's gut.

Exactly half, 15, of the stool samples turned out to contain detectable levels of exactly the same bacterial strain that had caused the bloodstream infections. Because the gut normally contains more than 1,000 different bacterial strains, it is assumed to be a probable culprit for bloodstream infections. However, prior to the Stanford study, this assumption had not been proven.

The study did not find much evidence that a patient's bloodstream pathogen matched microbial strains found in blood or stool samples of other patients, contrary to what is often assumed.

Source: MedicalXpress, October 15, 2018

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