Sensitivity of Commercially Available Dengue Virus PCR Assay Evaluated

Taiwanese researchers have concluded that the LightMix® Dengue virus extraction control kit (Roche Diagnostics) was able to successfully detect the dengue virus (DENV) in serum samples collected from adults exposed to the virus in 2015, according to research published in PLOS Neglected Tropical Diseases.¹

The Lightmix assay is a commercially available quantitative real-time (qRT) polymerase chain reaction (PCR) assay utilizing array detection to detect DENV.

The study found that the LightMix assay yielded a linear curve for viral loads (VL) between 10² and 10⁶ copies per reaction.  Researchers found 88.9% agreement between results from the nonstructural protein 1 (NS1) antigen combo kit and the LightMix analysis. Diagnostic sensitivity for the NS1 antigen combo kit was 89.4% vs 100% for the LightMix assay. Specificity for the NS1 antigen combo kit was 84.7% vs 100% for the LightMix assay.

A dengue outbreak from August to November in Tainan, Taiwan resulted in 22,563 confirmed infections and 112 deaths. Researchers at the Clinical Virology Laboratory of National Cheng Kung University Hospital collected serum samples from patients with infections categorized as mild, severe, or fatal according to World Health Organization criteria, and 1581 patients with suspected DENV.

Researchers screened sera using the one-step immunochromatographic Dengue DuoDengue NS1 Ag + Ab Combo assay that can simultaneously detect levels of NS1 antigen, and IgM and IgG within 15 minutes.

A total of 8989 samples were screened for NS1 antigen, 8954 samples for IgM and, IgG detection, and 1581 for qRT-PCR assay analysis. Another 8954 samples were screened via a rapid combination test for antigen and antibody detection for clinical diagnosis.

Samples collected from patients with suspected infections were simultaneously subjected to NS1 antigen, IgM and IgG, and qRT-PCR assay analyses. Of these samples, 41.8% tested positive for NS1 antigen, 11.2% for IgM, 6.9% for IgG, 6.9%, and 40.2% for DENV in the qRT-PCR assay.

The LightMix assay also detected DENV in 34 of the 44 samples collected from the fatal cases. Huey-Pin Tsai, from the Department of Pathology, National Cheng Kung University Hospital in Tainan, Taiwan, and colleagues noted that all of those samples, as well as 67 of 85 samples collected from patients with severe infections, tested positive for DENV2. None of those samples was positive for DENV1, DENV3, or DENV4.

“Accurate, rapid, and early diagnosis of DENV infections could reduce the risk of development of life-threatening dengue illness, particularly in NS1/IgM/IgG-negative cases,” wrote Tsai and colleagues. “Our results indicate that this LightMix dengue virus EC qRT-PCR assay could be helpful in predicting mortality in primary infected elderly patients, for early diagnosis of DENV infections, and for controlling future dengue outbreaks.”

Reference

1. Tsai H-P, Tsai Y-Y, Lin I-T, Kuo P-H, et al. Validation and application of a commercial quantitative real-time reverse transcriptase-PCR assay in investigation of a large dengue virus outbreak in Southern Taiwan. PLoS Negl Trop Dis. 2016; 10: e0005036. doi: 10.1371/journal.pntd.0005036.