The fact that an applesauce has tested positive in a rapid test does not prove that they are ineffective

Since the beginning of December, hundreds of users have shared a video that they say would demonstrate that rapid antigen tests for COVID-19 are not reliable. When recording, a test gives a positive result for a sample of applesauce. However, the reaction of the kit does not support the claim that this diagnostic tool is ineffective. What it reveals is that your results are invalid if the procedure does not follow the manufacturer’s instructions.

The 2:15 minute video has been shared since December 9 on Facebook (1, 2, 3) and Twitter. In it, a person shows a covid-19 antigen test and a small packet of applesauce. He then opens the container and, using what appears to be a cotton swab, collects a sample of the applesauce and sends it to the diagnostic kit. After a while, the person holds the test in front of the camera – the result is positive.

“Positive covid test with apple dessert … seems to explain the large number of people infected with covid … and the flu is gone”wrote one user when posting the video.

Similar publications circulate in English, Spanish, German and French.

The tests available to detect COVID-19 can be divided into three categories. The first includes PCR (polymerase chain reaction) tests, which analyze whether there is a very specific part of the new coronavirus genome in the sample, using a biochemical process. The Robert Koch Institute (RKI) calls this type of test, used by laboratories around the world, the “gold standard” for diagnosis.

The second is that of serological tests, which check if a person has antibodies to SARS-CoV-2 in the blood. Scientists use this method to calculate how many people have had an infection. The government of the city of Buenos Aires, for example, used it to determine that 10.1% of its population had the disease in mid-September of this year.

Finally, there are antigen tests, which are less accurate than PCR tests, but provide results more quickly. These tests are also less sensitive than PCR tests, which means that they need a higher viral load to identify infection. This means that, especially if the infection occurred recently, the antigen test can give “false negatives.”

PCR detects the genetic material of the new coronavirus, while antigen tests are designed to identify the molecules that surround the virus.

The AFP control team has already seen a similar video in which Polish paramedics subject a fruit juice to rapid antigen testing and, on that occasion, they consulted Juan Sabatté, doctor in microbiology and researcher at the National Research Council Scientific and Technical (Conicet). from Argentina.

“These tests generally detect components of the SARS-VOC-2 virus using specific antibodies.”, said. When identified, a reaction with colors and “Band-shaped (the line that appears indicates that it is positive)”.

The United States Food and Drug Administration (FDA) indicates that “Positive antigen test results are very accurate”, but warns about “A higher probability of false negatives, which means that negative results do not rule out the possibility of infection”. If the patient receives such a result, the FDA recommends confirming it with a PCR test.

A study published by researchers at the Berlin Medical University Charité, not yet peer-reviewed, concluded that there are differences in the quality of these tests, but that most have a high level of specificity.

Examining the video

The test you see in the video is one of the type of antigens, more precisely the “Rapid MEDsan SARS-CoV-2 Antigen Test”. The manufacturer’s logo can be easily identified on the engraving.

The MEDsan company product instructions indicate that the result is positive when two colored bands are seen. The document also details that the exam is only suitable for examining “Nasopharyngeal and / or oropharyngeal secretions in humans” and that the proof “Not designed for use with other body fluids and samples”.

AFP did not detect any obvious manipulation in the viral video. Asked by the AFP verification team, Kai Markus Xiong, a MEDsan spokesman, also did not doubt the authenticity of the video. However, he noted that it is not possible to see if the exam was performed correctly.

“We do not know if the person in the video is infected with the coronavirus and if the test was stored correctly”, said. Added that “Proper and professional decontamination is not possible” when working on a cloth surface, as appears to be the case with video.

At the request of AFP, MEDsan conducted its own experiment to recreate the result shown in the video. Two employees who tested negative on the PCR test tested various substances for antigen, including alcohol-based disinfectants, strawberry jam, glass cleaner, apples, and apple juice. As a result, they got two positives for the disinfectant and one weak positive for the jelly.

For MEDsan, the results of these tests do not contradict the reliability of their kits: “We did not develop this product [para ser usado com] applesauce is not our job “. Their objective, they explained, is for the test to present reliable results in humans and, therefore, the result when used in food does not raise doubts about its effectiveness in detecting SARS-CoV-2.

“The test should be considered as a tool to be used by trained professionals”Xiong added. Professionals should ensure that factors that could change the result, such as food, do not affect the test. “You also won’t be with your mouth full doing a test like that”, said.

Correct conditions

AFP showed the video to experts in immunology and biochemistry, who also noted that the conditions under which the test is performed, particularly the acidity level, are crucial to obtaining a valid result. Furthermore, they emphasized that these tests are designed to be used only with the samples for which they were evaluated.

“It is not an achievement to distort the conditions of a test until it gives false results”Thomas Decker, professor of immunobiology at the University of Vienna, told AFP. “The test was developed to allow an antibody to bind to antigens, not to react to certain foods.”he added.

The expert was forceful and compared the experiment viralized in the networks to affirm that “A car no longer works if we put applesauce in the tank [de gasolina]“.

Along the same lines, Anette Beck-Sickinger, a professor of biochemistry at the University of Leipzig, Germany, stated that this test, like any biochemical process, “It can only work if done under the right conditions”.

To perform an antigen test under the proper conditions, the sample must first be immersed in a buffer solution, which allows the pH value to stabilize. However, this solution “It is not capable of neutralizing large amounts of acid (such as an apple or a mango)”Beck-Sickinger explained.

Modifying test conditions, such as pH or temperature, can “Cause a non-specific antibody reaction”, causing a false positive, he detailed. That is, an incorrect application of the test leads to incorrect results.

In summary, the viralized video does not demonstrate that antigen tests are not capable of detecting covid-19, but they can give incorrect results if performed under inappropriate conditions, without respecting the manufacturer’s instructions. Although rapid tests are less reliable than other methods, such as PCR tests, if used correctly they can indicate the existence of a new coronavirus infection.