Should the sampling swabs used for coronavirus nucleic acid detection and antigen detection be sterilized? Why does it turn yellow?

       In the current epidemic situation, the detection of covid-19 nucleic acid and antigen is indispensable. I believe everyone has a lot of contact with the small sampling swab during nucleic acid and antigen detection. However, many people are still worried about whether the small sampling swab has been sterilized. Why does the swab turn yellow and will it affect us?

       Sampling is the first step of testing. Many friends have questions about whether the disposable sampling swab is “sterilized” or “non sterilized”, and whether it needs to be sterilized. Let’s take a look at these questions

1. What material is generally used for sampling swabs?

      Disposable collection swabs are different from cotton swabs used in daily life and belong to medical device products.

      Common sampling swab head materials include flocking, sponge, etc. It shall have the characteristics of easy elution, no toxic effect on pathogens and contacted cells and tissues, and no impact on subsequent detection.

2. What is “sterile” and what is “non sterile” / “non sterile”

       [sterility]: refers to the state without viable microorganisms. After sterilization, the theoretical probability of the existence of viable microorganisms should not exceed the negative 6th power of 10. Therefore, in some use environments with high requirements, “sterile” medical devices are required.

       [non sterile / non sterile]: Although this kind of medical devices can not be as strict as “sterile” medical devices, which are almost “free of bacteria”, they are not “dirty”. All medical devices must meet certain health requirements, such as strictly controlling the number of microorganisms, before they can be qualified for marketing.

      The sampling head is the core part of a disposable sampling swab. Take it as an example, the sampling head of a common cotton swab can be made of medical absorbent cotton, polyester staple fiber, electrostatic flocking fabric and other materials. If the “non sterile” medical absorbent cotton is used, it must comply with the Chinese pharmaceutical industry standard medical absorbent cotton. The manufacturer must provide the microbial limit for the reference of medical institutions and other users.

3. Will the sampling swab with “bacteria without sterilization” affect the antigen detection?

      This is a misunderstanding caused by confusing bacteria and viruses.

      It should be noted that the antigen detection “looks for” the N protein of novel coronavirus carried by the covid-19 infected person. The display window of the reagent strip contains an antibody that can recognize the viral protein, which is like a dam. It can only intercept the antibody latex / colloidal gold conjugate that binds to the viral antigen, and present it in the form of antibody antigen antibody latex / colloidal gold (referred to as double antibody sandwich method) so as to develop color in the display window. Therefore, even if the sampling swab carries “bacteria”, the detection reagent card will “ignore” and focus on finding the N protein of novel coronavirus carried by the coronavirus infected person. Since the reagent card is not interfered by “bacteria”, the result of antigen detection will not be affected.

4. Is it necessary to sterilize the “non sterilized” / non sterilized “sampling swabs before use?

      It is not recommended to use household disinfectant to disinfect the sampling swab head. The disinfectant may have the risk of destroying the sampling sample, thus affecting the original test results. The sampling swab is a medical device product, which is used to scrape the cells and virus samples into the extraction solution / virus preservation solution for relevant detection. The qualified sampling swab is non-toxic and harmless.

5. Why are some sampling swabs “yellow”, and how is it caused?

      As mentioned above, some sampling swab heads are made of sponge (also known as polyurethane foam), which will cause thermal oxidation yellowing under light (UV) and high temperature conditions or gas fumigation yellowing caused by contact with nitrogen oxides (NOx) in the air due to the characteristics of the swab materials. This is an inevitable phenomenon in the current production process of polyurethane foam, so it is recommended to store it at 2-30 ℃ away from light to avoid or slow down yellowing.

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