Question: I’ve been developing a bit of a cough and have a bit of a scratchy throat. I thought it might be allergies, but I’ve never had them before. Is there any way to differentiate between allergy symptoms and COVID-19?

Answer: Obviously, I’m not a doctor. If you’re concerned about your health, definitely talk to your doctor and always pay attention to your body. And if you feel sick, please stay home, call your doctor, and take action based on that conversation. All that preamble said, this is a great question and one that many of us are asking. Per Weather Channel, tree pollen in DC is HIGH right now. And if you’re not from the DC area, even if you’ve lived here for a couple of years, it’s likely that allergies will hit you harder. Here’s a great article on the topic. Now when it comes to differentiating allergies and COVID-19 symptoms, there are a few things that make the two very different. First, you will NOT have a fever with allergies, but you generally WILL have a fever with COVID-19. Second, you generally will have sneezing and a scratchy throat with allergies, but you will generally NOT have those symptoms with COVID-19. As with all my answers, we’re operating with limited data. We do know that clinical characteristics out of China among those hospitalized show that “the incidence of fever was 89.1%, the incidence of cough was 72.2%, and the incidence of muscle soreness or fatigue was 42.5%… Diarrhea, hemoptysis, headache, sore throat, shock, and other symptoms only occur in a small number of patients.”

Question: I saw there were reports that President Bolsonaro in Brazil tested positive for COVID-19 and then an hour later another test was apparently negative. Is there a way of knowing which one was the false one?

Answer: This question is both a political one and a science one. On the politics side, one has to think about the benefits and drawbacks of a country’s leader admitting to illness. Add that with the information flow on social media and challenges abound. I’m going to set aside the political piece now and focus on the science piece. It is possible to have a false positive (e.g. test says your positive but you really aren’t), just as it is possible to have a false negative (e.g. test says you’re negative, but you really have the virus). In the case of COVID-19, false-negatives are more likely. For false positive COVID-19 tests, it’s generally because of test contamination. This is lab-based error and is, to my knowledge, quite rare [see more about PCR tests in the Q&A from 3/9]. Meanwhile, a negative test result does not necessarily mean that the person is not infected with COVID-19. It means that the test did not pick up any of the virus in the sample, which could be because of a variety of factors. LabCorps has a good description of those factors here. Finally, if I were tested and learned that one test was positive and one negative, I’d assume I was positive, especially since I was presumably tested because I was likely exposed and/or exhibiting symptoms.