University of São Paulo: RT-LAMP test developed on the Pasteur-USP Scientific Platform identifies coronavirus in 30 minutes

The Pasteur-USP Scientific Platform (SPPU-USP), in partnership with the Oswaldo Cruz Foundation (Fiocruz) of Curitiba, developed a test for the diagnosis of covid-19 using the RT-LAMP technique (reverse transcriptase – isothermal loop-mediated amplification) , a more affordable method that can help extend diagnostic coverage. In an article published in Scientific Reports , the researchers showed that the test has a sensitivity of 90% (ability to detect positive cases) and 100% specificity (ability to exclude negative cases). The few RT-LAMP tests available on the market today reach, at most, 95% specificity.

It is a simple colorimetric reaction test, which can be done by collecting saliva or secretions from the nasopharynx. Samples are placed in small tubes with pink staining reagents, which change color to yellow in the presence of coronavirus. Although it also depends on imported reagents, LAMP costs 1/3 of the cost of PCR, the gold standard test, and does not require expensive equipment, being considered a good strategy to popularize the diagnosis. “What makes PCR so expensive is the equipment, which costs more than R$ 200,000 – few laboratories have access. LAMP can be done in any laboratory, even in schools”, says virologist Edison Durigon, from the Institute of Biomedical Sciences (ICB) at USP, one of the study coordinators.

Unlike RT-PCR, which uses equipment that requires different temperatures, RT-LAMP is an isothermal test, performed at a single temperature. The result comes out the same day or the next day. “The PCR is a more sophisticated reaction, which takes about 3 hours. It needs three temperatures (varies between 90°C, 65°C and 60°C) to make multiple copies of the RNA strand. In the LAMP, the primers are placed in a water bath at 65ºC and, in 30 minutes, you have millions of copies. The solution changes color when it detects the presence of the virus”, explains the researcher.

The patient’s viral load, however, ends up being a limitation: if the amount of virus is too low, the test can give an inconclusive result, generating an orange color. In this case, the test must be repeated or confirmed with an RT-PCR to avoid a false diagnosis. “In the PCR, from the third day of infection onwards, it is already possible to identify the virus. LAMP should be done from the fifth day onwards, so that there is enough viral load to be detected”, he emphasizes.

There is still no forecast when the test will be available on the market, but Durigon says that some private companies are already interested in developing it, in addition to Fiocruz itself. One of the advantages is that, while the commercial tests are patented, the SPPU test has all the information open to the scientific community, enabling its reproduction. “Our main intention is to contribute to science. Whether this is going to become a product depends a lot on the companies, on who will buy it to produce it on a large scale.”

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