A confirmed case of coronavirus disease 2019 (Covid-19) was defined as one in which a nasopharyngeal swab specimen was positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by real-time reverse-transcriptase polymerase chain reaction. A suspected case was defined as one that met Council of State and Territorial Epidemiologists clinical criteria for Covid-19 without a positive test result. Confirmed cases were further classified as symptomatic (with symptom onset before the first positive laboratory test), presymptomatic (with the first positive laboratory test before subsequent symptom onset), and asymptomatic (positive laboratory test but clinical criteria never met).