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In that case, the antigen test wouldn't detect the virus. "What could feasibly happen is that someone could have a very low viral load in a nasal swab and not be detectable by the antigen tests, whereas they could have very high viral loads in saliva or throat or another specimen type - potentially infectious, viral loads." "We wanted to measure the viral load in each of those three specimen types, just to see if there's any differences in the dynamics there or how they evolve over time, and this has quite large implications for nasal antigen testing," Akana said. This doesn't mean the accuracy of at-home tests has declined, but rather researchers are better able to understand their limitations. "Then if we subsetted that to people who were infectious, meaning that they had high viral loads that are likely to be transmissible to other people, we found the performance was still fairly low - just above 60 percent," Viloria Winnett said. The authors of the study found that when looking at the performance of the test cross-sectionally, at-home antigen tests are only 44 percent accurate. "There are a lot of studies out there with kind of conflicting results, likely because the population that is actually doing the test makes a big difference for how well the tests performed." "We wanted to ask the question: How well do the rapid antigen tests detect people who are infected, and how well the rapid antigen tests detect people who are not just infected, but actually infectious and capable of transmitting the virus to other people?" Alexander Viloria Winnett, biology graduate student and study co-author, told Salon. Want more health and science stories in your inbox? Subscribe to Salon's weekly newsletter The Vulgar Scientist. Specifically, that the virus appears in a person's throat and saliva first, and then their nose. While they expected to observe similar virus levels in the three locations, their results told a different story that started to raise complexities and questions around at-home tests. In the new study, researchers at California Institute of Technology tracked viral loads in three places of the human body - nose, throat and mouth - over the course of a COVID infection. While it varies by brand, at-home tests generally work when a person swabs their own nostrils and then exposes the sample to a liquid chemical, which will then determine if they are positive or not by detecting the presence of the antigen being tested. The presence of antigens is an indicator that a patient has the SARS-CoV-2 virus, which causes COVID. At-home tests function by detecting the presence of substances called antigens that stimulate an immune response against COVID.