Inclusion Criteria:  be aged 21 years and older; be a resident of the USA; have a personal (i.e., not shared) iPhone 6s or newer running iOS 14 or later; be able to read and understand English; be able to provide informed consent; be willing to follow study procedures; be able to provide at least 5 coughs (voluntary and/or spontaneous); have enrolled in the COVID-Cough Study and successfully returned an at-home rt-qPCR test to the study partner laboratory  Exclusion Criteria:  Participant has one or more medical contraindication to voluntary cough, including the following:  Severe respiratory distress; History of pneumothorax; Eye, chest, or abdominal surgery within 3 months of enrolling for the study; or Hemoptysis (coughing up of blood) within 1 month of enrolling for the study;