A group of CSIC researchers have found a way to detect with a PCR test, without the need for subsequent culture, if SARS-CoV-2 is alive or dead in the body. This tool, the main one to diagnose COVID-19, did not discriminate until now if the virus was dangerous for transmission. Scientists from the Institute of Agrochemistry and Food Technology, led by biologist Gloria Sánchez, have applied a treatment to the sample that allows the signal to be eliminated when the pathogen is inactive.
"We do the same procedure that we would do with a normal sample, but before doing the nucleic acid extraction, we proceed to the treatment of the sample. If the virus is inactive or the RNA is loose, the signal is not detected by PCR," he explains Sánchez, head of the Environmental Virology and Food Safety research group.
The PCR is very sensitive - to the minimum trace that it detects of viral RNA it is positive - and fast, but "without culturing the samples you are left with the doubt whether the virus is infectious or not," adds the researcher, who has already applied this same technique with other viruses in the field of food safety. Treatment makes the procedure easier: SARS-CoV-2 cell culture is complex because you have to work in a special laboratory, and that takes time and resources.
The Hospital Clínico de Valencia has collaborated in the research by providing the samples. At the clinical level, progress is useful, according to the researchers, in the cases of patients with positive CRP for months. Through a simple procedure, false positives can be detected, that is, people who do not infect despite the presence of virus RNA in their body and thus avoid isolation, says Carmen Cámara, secretary of the Spanish Immunology Society.
"Immunologists asked each other: and you, what do you do with immunosuppressed patients who test positive for 8, 12 or 16 weeks? Well, we kept them locked up as a precaution. Although we had the certain feeling that they were not infectious, but so far not We could demonstrate it with an easy laboratory test ", Chamber abounds, in a telephone conversation with elDiario.es.
The Spanish Society for Infectious Diseases and Clinical Microbiology underlined in a document, published a year ago, that "the detection of viral RNA" in a PCR "does not necessarily imply the presence of infective virus in clinical samples." Although it has been the most used technique throughout the pandemic, the results raised doubts when taking public health measures since PCR can detect viral RNA for very long periods and not always be related to a virus with capacity to infect.
The CSIC team has also discovered, through this technique, that wastewater "is not a vector for the transmission of the coronavirus" since the pathogen is inactivated in the samples they took. Sánchez explains that knowing if the virus was active was interesting for their field of research because it has allowed them to know if the treated waters, and used for irrigation, can preserve infectious pathogens. The Ministry for Ecological Transition launched an epidemiological surveillance tool together with Health to sample and analyze wastewater weekly.
"It is also interesting to rationalize the surface washing measures that people have done. It can make it possible to demonstrate that contagions through this route, as most of us suspect, do not exist and that most are produced through the air," adds Cámara.