Use of LoopDeelab during the COVID-19 Pandemic: An Innovative Device for Field Diagnosis

Abstract

Rapid and accurate diagnosis of SARS-CoV-2 infection is essential for the management of the COVID-19 outbreak. RT-LAMP LoopDeetect COVID-19 (LoopDeescience, France) is a rapid molecular diagnostic tool which operates with the LoopDeelab (LoopDeescience, France) device. RAPID COVID is a prospective double-blind research protocol which was conducted to evaluate the concordance between Loopdeetect COVID-19 and RT-PCR Allplex 2019 n-Cov (Seegene, Korea). Between 11 May 2020 and 14 June 2021, a total of 1122 nasopharyngeal swab specimens were collected, of which 741 were finally analysed. There were 32 "positive" and "indeterminate" RT-PCR results. The intrinsic performances of Loopdeetect COVID-19 are equivalent to other commercial RT-LAMP PCR COVID-19 kits, with a sensitivity and specificity of 69.23% [CI 95%: 48.21-85.67] and 100% [CI 95%: 99.58-100.00], respectively. To the best of our knowledge, LoopDeelab is the only LAMP PCR diagnostic device allowing such a fast and reliable analysis with low-cost equipment; this makes it a new and innovative technology, designed for field use. This device being portable, the development of other detection kits will be useful for the management of epidemics with a high attack rate and would facilitate the rapid application of health measures.

Keywords: COVID-19; LAMP PCR; Loopdeelab; Loopdeetect; RAPID COVID; SARS-CoV-2.

Figure 1

Sampling and testing site modifications. The first line shows the different testing sites and temperature conditions. The second line shows the different sampling and analytical methods. * RT-qPCR: Allplex 2019 n-Cov assay kit, Seegene, Korea. ** LAMP PCR: LoopDeetect COVID-19, LoopDeescience, Caen, France.

Figure 2

RT-LAMP assay (LoopDeetect COVID-19). After blowing the patient’s nose, the nasopharyngeal swab was performed with a flocked swab (a) and then placed in a liquid medium. After homogenisation, 25 µL of the liquid medium (b) were added to 475 µL of dilution buffer containing Tris EDTA (c). After homogenisation, 25 µL were added to a 1.5 mL microtube containing a lyophilised mix, including Master mix RT-LAMP and DNA-primer mix (d). The reaction tube carrying the sample was directly inserted into the LoopDeelab chamber (e). The scan was started by pressing the button on the device. The result was given directly without opening the tube, thus preventing contamination. The LoopDeelab (Loopdeescience, Caen, France) device concentrates technologies allowing us to heat the reaction tube and read different wavelengths after excitation by LED. A specific programme stored within the motherboard microprocessor controls the temperature and the wavelengths’ emission and reading (using diodes and spectrophotometer). An artificial intelligence calculates the figure of merit and gives a false or true result displayed directly on the LoopDeelab (red and green lights for positive and negative results, respectively).

Figure 3

LoopDeelab device.

Figure 4

RAPID COVID study results flow chart. The first line of the flow chart shows the number of patients enrolled during the three inclusion periods. The second line shows the number of patients that were included in the analysis and the reasons why some were excluded. The third line shows the number of “positive” or “indeterminate” samples and the proportion of symptomatic patients. The red vertical dotted lines indicate protocol changes.

Figure 5

Evolution of sensitivity of LoopDeetect COVID-19 according to Ct RdRp values. Allplex 2019 n-Cov assay kit (Seegene, Korea) was the gold standard for calculation of sensitivity. The blue, red and green curves represent the entire, symptomatic and asymptomatic populations, respectively. The red vertical line indicates the threshold Ct = 33.

Figure 6

Box plots of Ct RdRp distributions in different groups. Ct RdRp distributions in the entire population (left), symptomatic group (middle) and asymptomatic group (right).