Background COVID-19 is an infectious disease characterized by various clinical presentations. Knowledge of possible symptoms and their distribution allows for the early identification of infected patients. Objective To determine the distribution pattern of COVID-19 symptoms as well as possible unreported symptoms, we created an app-based self-reporting tool. Methods The COVID-19 Symptom Tracker is an app-based daily self-reporting tool. Between April 8 and May 15, 2020, a total of 22,327 individuals installed this app on their mobile device. An initial questionnaire asked for demographic information (age, gender, postal code) and past medical history comprising relevant chronic diseases. The participants were reminded daily to report whether they were experiencing any symptoms and if they had been tested for SARS-CoV-2 infection. Participants who sought health care services were asked additional questions regarding diagnostics and treatment. Participation was open to all adults (≥18 years). The study was completely anonymous. Results In total, 11,829 (52.98%) participants completed the symptom questionnaire at least once. Of these, 291 (2.46%) participants stated that they had undergone an RT-PCR (reverse transcription-polymerase chain reaction) test for SARS-CoV-2; 65 (0.55%) reported a positive test result and 226 (1.91%) a negative one. The mean number of reported symptoms among untested participants was 0.81 (SD 1.85). Participants with a positive test result had, on average, 5.63 symptoms (SD 2.82). The most significant risk factors were diabetes (odds ratio [OR] 8.95, 95% CI 3.30-22.37) and chronic heart disease (OR 2.85, 95% CI 1.43-5.69). We identified chills, fever, loss of smell, nausea and vomiting, and shortness of breath as the top five strongest predictors for a COVID-19 infection. The odds ratio for loss of smell was 3.13 (95% CI 1.76-5.58). Nausea and vomiting (OR 2.84, 95% CI 1.61-5.00) had been reported as an uncommon symptom previously; however, our data suggest a significant predictive value. Conclusions Self-reported symptom tracking helps to identify novel symptoms of COVID-19 and to estimate the predictive value of certain symptoms. This aids in the development of reliable screening tools. Clinical screening with a high pretest probability allows for the rapid identification of infections and the cost-effective use of testing resources. Based on our results, we suggest that loss of smell and taste be considered cardinal symptoms; we also stress that diabetes is a risk factor for a highly symptomatic course of COVID-19 infection.

BACKGROUND COVID-19 is an infection characterized by various different clinical presentations. Knowledge of possible symptoms and their distribution allows an early identification of infected patients. OBJECTIVE To determine the distribution pattern and possible unreported symptoms an app-based self-reporting tool was created. METHODS The COVID-19 Symptom Tracker study is an app-based daily self-reporting study. Between 08 April and 15 May 2020, a total of 22,327 individuals installed the smartphone app (COVID-19 Symptom Tracker) on their mobile device. An initial questionnaire asks for demographic information (age, gender, post code) and a past medical history with relevant chronic diseases. The participants are notified daily to report whether they are suffering from current symptoms and have been tested for SARS-CoV-2. When seeking healthcare advice additional questions regarding diagnostics and therapy are asked. Participation is open for every adult (minimum age 18 years). The study is completely anonymous. RESULTS 11,829 (52.98%) participants completed the symptom questionnaire at least once. 291 of these participants stated that a RT-PCR test for SARS-CoV-2 was performed. 65 reported a positive and 226 a negative test result. The mean average number of reported symptoms in the group of untested participants was 0.81 (SD: 1.85). Participants with a positive test showed a mean average of 5.63 symptoms (SD: 2.82). Most significant risk factors are diabetes (OR: 8.95; CI: 3.30-22.37) and chronic heart disease (OR: 2.85; CI: 1.43-5.69). We identified chills, fever, loss of smell, nausea and vomiting and shortness of breath as the top five of the strongest predictors for a COVID-19 infection. The odds ratio (with 95% confidence interval) for loss of smell was 3.13 (1.76-5.58). Nausea and vomiting (OR: 2.84; CI: 1.61-5.00) has been reported as an uncommon symptom however our data suggest a significant predictive value. CONCLUSIONS Self-reported symptom tracking helps to identify novel symptoms of the COVID-19 disease and estimate the predictive value of certain symptoms. This helps to develop reliable screening tools. A clinical screening with a high pre-test probability allows the rapid identification of infections and a cost-effective use of testing resources. Our data stress the necessity for an awareness of loss of smell and taste as a cardinal symptom and suggest that diabetes is a risk factor for a highly symptomatic course of a COVID-19 infection. CLINICALTRIAL DNA