Automated System Diagnoses Respiratory Infections

The assay technology, called Respiratory Virus Nucleic Acid Test SP (RVNATsp), is 98% sensitive and 96% specific. By comparison, the conventional alternative, the culture methods are nearly 100% specific, but only 70% sensitive.

In a study carried out at the Medical College of Wisconsin, (Milwaukee, WI, USA), clinical nasopharyngeal swab specimens were assayed by nucleic acid-based tests: the semiautomated respiratory virus nucleic acid test (VRNAT) and the fully automated respiratory virus nucleic acid test SP (RVNATsp). This microarray was tested on 720 patient samples collected throughout the US. Detection of viral ribonucleic acid (RNA) in both tests is based on nucleic acid amplification followed by hybridization to capture probes immobilized on a glass slide. A novel technology utilizing gold nanoparticle-conjugated probes is utilized to detect the presence of captured target DNA. This microarray-based approach to detection has proven to be more sensitive than the traditional culture/direct fluorescent-antibody assay (DFA) method for detecting RSV and influenza viruses in clinical specimens.

Evaluation of the fully automated RVNATsp, which is built on the same detection technology as the VRNAT but contains an updated processor enabling complete automation, revealed the two tests to be functionally equivalent. Thus, the RVNATsp is a fully automated sample-to-result test capable of reliable detection of select respiratory viruses directly from clinical specimens in 3.5 hours. The tests are made by Nanosphere (Northbrook, IL, USA) as part of their Verigene Systems. The VRNAT is a semiautomated predecessor to the automated RVNATsp. The test combines external nucleic acid extraction and reverse transcriptase polymerase chain reaction (RT-PCR) with Nanosphere's proprietary nanoparticle hybridization technology for detection and identification of Influenza A, Influenza B, and RSV on the Verigene System.

Nathan A. Ledeboer, PhD, the lead author of the study, said," Instead of relying on insensitive but rapid influenza tests for diagnosis in the clinic, or waiting 24 hours or more for molecular results to come back, we can now provide molecular level sensitivity in less than three hours. This will mean that hospitalized patients with influenza and RSV infections will be isolated faster, which will decrease the risk of transmission to other patients in the hospital." The study was published in November 2010, in the Journal of Clinical Microbiology.

Related Links:
Medical College of Wisconsin
Nanosphere