IntroductionMobile health applications are increasingly being used in health and clinical research. SARS-CoV-2 has proven to have high infectivity, making outbreaks difficult to contain. Early detection can help prevent spread, but there is a need to develop easy-to-use screening tools that can help identify potential infection as early as possible. Here, we describe the development of a machine learning classifier that can predict SARS-CoV-2 PCR positivity using smartphone-submitted vital sign measurements.MethodsThe Fenland App study followed 2,199 UK participants using a smartphone application from August 2020 and for a minimum of six months. Participants completed a baseline questionnaire and then monthly questionnaires about SARS-CoV-2 status and vaccinations. Three times a week, participants provided measurements of their blood oxygen saturation, body temperature, and resting heart rate via a pulse oximeter, digital thermometer, and their smartphone. The participants participated in self initiated SARS-CoV-2 testing as per concurrent public health guidelines.We built predictive models SARS-CoV-2 PCR positivity status as obtained from national surveillance PCR test results.ResultsA total of 77 positive and 6,339 negative SARS-CoV-2 tests were recorded during the study. The final model achieved an ROC AUC of 0.695 ± 0.045. There was no difference in model performance when using 4, 8 or 12 weeks of baseline data before a SARS-CoV-2 test (F(2) = 0.80, p = 0.472). Addition of demographic or symptom information had no impact on model performance.ConclusionsUsing only three smartphone collected vital sign measurements, it is possible to predict SARS-CoV-2 PCR positivity, using a four week baseline period. Smartphone based remote monitoring of patient vital signs could allow for earlier screening for potential infections. This method could be applicable to any infectious disease that causes physiological changes in vital signs.