My guess is Covid based only on symptoms. Here's why, accurate Half the Time:
Accuracy during the first week of symptoms versus the second:
Rapid tests more accurately provided a positive COVID-19 result when administered during the first week of symptoms. The researchers found that rapid tests correctly identified COVID-19 in an average of 78.3 percent of cases during the first week.
In the second week, the average dropped to 51 percent.
Differences between brands:
The researchers found a large range of accuracies between manufacturers of the tests.
Coris Bioconcept scored the poorest and correctly provided a positive COVID-19 result in only 34.1 percent of cases. SD Biosensor STANDARD Q had the highest score and correctly identified a positive COVID-19 result in 88.1 percent of people.
In another study Trusted Source published in April 2021, researchers compared the accuracy of four types of COVID-19 rapid antigen tests. The researchers found that all four tests correctly identified a positive COVID-19 case about half the time.