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Technological Contents in Virus Sampling Tube

Views: 0     Author: Site Editor     Publish Time: 2022-11-22      Origin: Site


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Technological Contents in Virus Sampling Tube

The COVID-19 pandemic keeps resurging in China and making the prevention situation critical. The quality of nucleic acid testing for COVID-19 plays an important role in prevention situation. Currently, virus sampling tubes are only required for Class I medical records, but products in market are varied in different qualities. The focus of bidding parameters is superficial, often concentrating on the material, specification and size of the sampling tubes, for inactivated sampling tubes or not, etc., ignoring more critical preservation performance indicators, which increases the difficulty of implementing the dynamic zero-Covid policy and tackling the impact of COVID-19 via targeted means.

I. What is a virus sampling tube and what is its function?

Virus sampling tubes are a kind of disposable testing consumables used to preserve the activity of virus samples or to maintain the stability of nucleic acids in samples.

The virus sampling tube is generally composed of three parts: a disposable sampling swab, a disposable virus sampling tube and a biological safety bag.

The red liquid in the virus sampling tube is the virus preservation solution, which can be divided into inactivated and non-inactivated types. According to the Implementation Guidelines for the Organization of Regional COVID-19 Nucleic Acid Test (Third Edition), it is suggested that the sampling tube containing guanidinium salt (guanidinium isothiocyanate or guanidinium hydrochloride, etc.) or surfactant should be selected for population screening. It has the advantage of quickly inactivating the COVID-19 in swabs, preventing cross infection in detection, inhibiting the activity of nuclease, and maintaining the stability of viral nucleic acid.

II. Technology content and performance index of swab

The disposable sampling swab is made by flocking technique with nylon fluff sprayed vertically onto glued ABS rods. With it, epithelial exfoliated cells from collected patient lesions can be detached and released into the preservation solution for viral detection in a complete and rapid manner.

(1) Advantages of nylon flocking swab

High adsorption: The adsorption efficiency of nylon flocking swab is 20%-60% higher than that of other swabs.

Fast collection: Flocked nylon swabs take only 3 seconds to 11 seconds to absorb and collect samples; while cotton swabs take up to 15 seconds to 120 seconds to collect samples.

High release: A domestic pathogen collection experiment found that the release efficiency of flocking nylon swab after pathogen collection was almost similar to that of the swab-free positive control group at different dilution concentrations; while the release efficiency of pathogens collected from cotton swabs was significantly lower, and the results were more affected by the dilution concentration.

(2) Safety of swab to human body

The regular monitoring of the pandemic has made nucleic acid screening a daily part of life, with three or four tests a week, and even some service industry personnel need to conduct daily nucleic acid testing, where swabs need to come into direct contact with the oral and nasal mucosa, so the safety of swab cannot be ignored.

ISO 10993-10: 2010 Biological Evaluation of Medical Devices - Part 10: Tests for Irritation and Skin Sensitization assesses the biosafety of sampling swabs from three separate dimensions, namely cytotoxicity, skin irritation and skin sensitization, to help us select sampling swabs that are safe for human body.

III. Technical specifications of virus sampling tube

The swab samples stored in the virus sampling tube need to be sent to the molecular laboratory for nucleic acid detection. Since the genetic material of the COVID-19 is RNA, which is extremely unstable in nature and easily degraded at too high a temperature, and the nuclease enzymes found everywhere can also cause its degradation. Therefore, the ability of the sampling tubes to stably preserve the RNA of the virus becomes the key to the accuracy of nucleic acid testing.

The quality of sampling tube is not only a matter of the visible indicators, but more importantly, the invisible indicators. The visible indicators include the directly observable quality indicators, such as the sampling tube material, process level, sealing, and filling accuracy. The invisible indicators include the preservation effect of viral nucleic acid, effect of the minimum detection limit, microbial indicators, virus inactivation efficiency, etc. These indicators are the key to determine the detection of viral nucleic acid.

Key indicator 1: Preservation effect of viral nucleic acid

The virus is inactivated in the preservation tube, releasing the genetic material RNA. Single strand RNA is extremely unstable in vitro, which is extremely prone to degradation and hydrolysis. The role of the virus preservation solution is to maintain the integrity of viral RNA and inhibit degradation and hydrolysis. Temperature, transportation conditions and storage days will all affect the integrity of RNA. The better the protection of RNA, the more accurate the nucleic acid detection of virus.

The preservation performance of different virus sampling tubes varies greatly. The above two brands of sampling tubes, A and D, have tested the nucleic acid detection results of viruses stored at 4 °C, 25 °C and 37 °C for 24 hours respectively. The Ct value of preservation tube A has almost unchanged from that of just sampled, indicating that the preservation effect is good, while the viral nucleic acid could not be detected in the preservation tube D from the 4th hour.


Key indicator 2: Preservation effect at minimum detection limit

The purpose of this indicator is to ensure that samples with low viral load can be detected without false negative misjudgment.

The national requirement is that the detection sensitivity of COVID-19 should not be higher than 500 copies/ml. In other words, as long as the sample concentration is not lower than 500 copies/ml, it should be detected. However, the reality is that after large-scale population screening or nucleic acid sampling in remote areas, the samples cannot be immediately sent to the laboratory for testing. The samples with low viral load may be degraded seriously to the concentration below 500 copies/ml, resulting in missed tests, i.e., false negative test results.

Key indicator 3: Microbial indicators 

Virus sampling tubes shall be manufactured by disposable non-toxic packaging and radiation inactivation process. The total aerobic bacteria (CFU/mL) ≤ 200; and total mold and yeast (CFU/mL) ≤ 100 are required.

The liquid in the virus sampling tube is the virus preservation solution, in which the color indicator phenol red is added. Under normal conditions, the liquid should be alkaline and purple red in color. Once the microorganism in the sampling tube fails to meet the requirement, its reproduction will cause the decrease of pH value of the liquid, and the preservation solution will turn from red to yellow. It can visually judge whether the microorganism reaches the requirement through the liquid color of the tube. The presence of microorganisms will accelerate the degradation of viral RNA and affect the sensitivity of nucleic acid detection.

Key indicator 4: Virus inactivation efficiency 

According to the notice in the Workbook for SARS-CoV-2 Nucleic Acid Test in Medical Institutions (Trial Edition 2), the population screening should select the sampling tube with the function of virus inactivation, such as guanidine salt (guanidine isothiocyanate or guanidine hydrochloride, etc.) or surfactant. Sample preservation solutions that directly inactivate the virus are highly desirable for the front line of the pandemic, which can greatly improve the safety of the sample collection and transportation process. It shall have high virus inactivation efficiency. As shown in the following table, the virus preservation tube can achieve 99.99% virus inactivation efficiency in 1 min.


With such a large demand for testing and market, there will inevitably be products of both good and bad in the market. But in the field of COVID-19 nucleic acid screening, which is related to the national economy and the people's livelihood, product quality is more important than price. We should adhere to the principle of quality first, ensure the accuracy of nucleic acid testing, and do not be penny wise and pound foolish.

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