Testing for sepsis takes days, which puts patients at danger. A novel approach could reduce wait times.

Treatment for bloodstream infections must begin quickly, although identifying the bacterium causing the infection may take many days. Researchers publish July 24 in Nature about a potential rapid-diagnosis sepsis test that could shorten testing times from several days to approximately 13 hours by eliminating the need for a drawn-out blood culture stage.

The research is pushing the boundaries of quick diagnosis for bloodstream infections, according to Penn State biomedical engineer Pak Kin Wong, who was not involved in the study. “They are moving in a direction that will significantly enhance the clinical treatment of sepsis and bloodstream infections.”

An immune system response to an infection, sepsis is a potentially fatal illness that affects around 2 million Americans annually and results in over 250,000 deaths (SN: 5/18/08). Additionally, the illness may worsen into septic shock, which is characterized by a sharp drop in blood pressure and harm to the liver, kidneys, lungs, and other organs. Since a wide variety of bacteria can cause it, species identification is essential for individualized patient care.

When doing a traditional sepsis test, the patient’s blood must first undergo a 24-hour blood culture in order to produce more germs that can be detected. After a second culture for purification, the sample is tested to determine the optimal course of action. Patients are given broad-spectrum antibiotics for the two to three days that testing takes; these are blunt instruments used to ward off an infection that is unclear at first and is better treated with tailored antibiotics once the particular bacteria causing the infection have been identified.

Tae Hyun Kim, a nanoengineer, and associates discovered a method to circumvent the initial 24-hour blood culture.

The first step in the workaround is to inject nanoparticles coated with a peptide that binds to a variety of blood-borne diseases into a blood sample. The bound germs accompany the nanoparticles when they are extracted by magnets. Direct delivery of those germs to the pure culture is made. According to Kim of Seoul National University in South Korea, the bacteria can multiply more quickly because of this binding and sorting mechanism, even in the absence of foreign substances like blood cells and the broad-spectrum antibiotics that were previously administered.

According to Kim, eliminating the first blood culture step also depends on a novel imaging technique. Scientists watch whether and how the antibiotics stop the bacteria’s development or kill them in order to assess the bacterium’s susceptibility to different antibiotics. Both types of bacteria are kept in the same environment. More subtle alterations than the human eye can pick up on are picked up by the team’s image detecting technology. Therefore, compared to the traditional method, it can detect the species and antibiotic susceptibility with considerably less bacterium cells, negating the need for lengthy culture durations to build larger colonies.

Wong notes that even if the new approach seems promising, there is always a chance that a novel test would miss bacteria that are truly in the bloodstream, leading to false negative results. According to him, “undertreatment of bloodstream infection can be fatal.” This can therefore result in failing to treat an active infection. “The classical blood culture technique is very effective in preventing false negatives, despite its extreme slowness.”

Kim and colleagues tested their new technique in 190 hospital patients with suspected infections in tandem with traditional sepsis testing after conducting laboratory-based experiments. According to the experts, the testing produced a 100% match for the accurate identification of the bacterial species. These accuracy results are good thus far, but further clinical testing is required, according to Kim.

In order to create a completely automated sepsis blood test that can generate findings fast—even during hospital lab closures—the team is still working to improve its design. Kim states, “We really wanted to make this happen and commercialize it so that we could affect the patients.”