UK researchers propose that seven symptoms considered together are the best indicator of COVID-19 infection in a community.

Imperial College London researchers and colleagues advised that being able to rapidly detect SARS-CoV-2 is essential to limit transmission. When testing capacity is strained, however, it is necessary to allocate tests using the most likely symptoms.

The study, with results published in PLOS Medicine, used throat and nose swabs with valid SARS-CoV-2 polymerase chain reaction (PCR) test results from 1.1 million volunteers in England aged 5 years and older. Researchers conducted eight testing rounds between June 2020 and January 2021 as part of the REal-time Assessment of Community Transmission-1 (REACT-1) study. They also asked participants about symptoms they had experienced in the week prior to testing.

Based on the data obtained in Rounds 2 to 7, a model was developed that listed seven symptoms that, jointly, were positively predictive of PCR positivity. The seven symptoms included loss or change of smell, loss or change of taste, fever, new persistent cough, chills, appetite loss, and muscle aches.

Only the first four of these symptoms are currently used in the UK to determine eligibility for community PCR testing.

The authors pointed out that in Round 8 of testing, their model predicted PCR positivity with an AUC of 0.77. Additionally, testing people in the community with at least one of the seven selected positively predictive symptoms yielded sensitivity, specificity, and positive predictive values of 74%, 64%, and 9.7%, respectively.

"The same 7 symptoms were selected as jointly predictive of B.1.1.7 infection in round 8, although when comparing B.1.1.7 with wild type, new persistent cough and sore throat were more predictive of B.1.1.7 infection while loss or change of sense of smell was more predictive of the wild type," the researchers explained. They noted that their modeling suggested that the use of the seven symptoms identified for PCR test allocation would result in 30% to 40% of symptomatic individuals in England being eligible for a test, versus 10%. If all of those eligible were tested, according to the researchers, 70% to 75% of positive cases could be detected.

"In order to improve PCR positivity detection rates and consequently improve control of viral transmission via isolation measures, we would propose to extend the list of symptoms used for triage to all 7 symptoms we identified," the authors said.

"These findings suggest many people with COVID-19 won't be getting tested—and therefore won't be self-isolating—because their symptoms don't match those used in current public health guidance to help identify infected people," stated lead author Paul Elliott, MBBS, PhD, FMedSci. He added, "We understand that there is a need for clear testing criteria, and that including lots of symptoms which are commonly found in other illnesses like seasonal flu could risk people self-isolating unnecessarily."

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