Researchers in the Milwaukee area have developed a new automated test to identify most leading causes of bacterial bloodstream infections 42 hours faster than conventional methods, potentially reducing medical bills by about $21,000 for patients suffering from sepsis.
The automated nucleic acid test, developed by researchers at Froedtert Hospital & The Medical College of Wisconsin and acompany called Nanosphere, identifies genetic information of bacteria and antibiotic resistance for 12 of the most common bacteria that cause sepsis.
Sepsis caused by bacterial bloodstream infections results in up to 500,000 hospitalizations each year and accounts for 11% of intensive care unit admissions in the United States, according to a study released Tuesday evaluating the effectiveness of the new test. It has a mortality rate of 25% to 80% in critically-ill patients. Gram-positive bacteria — which differ from gram-negative bacteria because of their thick cell walls — account for 52% to 77% of all bacterial sepsis.
Researchers for the study, published Tuesday in the journal PLOS Medicine, collected and tested 1,252 blood cultures containing gram-positive bacteria at five clinical centers across the country, including the Medical College of Wisconsin in Wauwatosa, between April 2011 and January 2012. An additional 387 contrived blood cultures with bacterial targets that are uncommon in the United States were included to further evaluate the performance of the test, named the Verigene Gram-Positive Blood Culture Test.
"We had looked at diagnosis of bloodstream infections and one of the major limitations ... was that results were taking a great deal of time to get to the patient," said the study's lead author, Nathan Ledeboer, an associate professor of pathology and medical director of microbiology and molecular diagnostics at Froedtert and the Medical College of Wisconsin. "What this panel allows us to do is look at a large percentage of those organisms and to report on a number of different resistance factors."
When compared with the commonly used reference culture method, the accuracy of the test — in terms of the number of true positives and negatives — ranged from 92.6% to 100% for all 12 of the gram-positive bacteria in the 1,157 collected cultures that contained a single target. About 7.5% of the cultures contained organisms that were not included on the panel.
Conventional methods take about three days to produce bacterial identification and antibiotic resistance results after the blood culture turns positive; the new test delivers the same results within 2.5 hours. Because of the long incubation period, patients with bloodstream infections are routinely treated with a broad spectrum of anti-microbials that are sometimes ineffective, leading to extended hospital stays.
While other techniques deliver results in as little as 30 to 60 minutes after blood culture positivity have been developed, most are limited to looking at just one milliliter of blood and thereby only one or a few specific target bacteria. The Verigene system can parse through 20 to 40 milliliters of blood and identify 12 gram-positive bacterial targets and three genetic markers of antibiotic resistance directly from the positive blood cultures, Ledeboer said.
"We're getting ready to use it," said Gary Procop, chair of molecular pathology at the Cleveland Clinic. "It gives a rapid identification of the organism and key resistant factors which is really important in tailoring therapy."
He added that the Verigene test is more user-friendly than the faster tests, because it's automated.
Froedtert has used the test for about 500 patients since the Food and Drug Administration approved it in September — and it's worked "exceedingly well," Ledeboer said.
The Verigene testing device itself costs between $10,000 and $20,000, and cartridges for individual blood cultures cost $75 each.