inclusion criteria: * a contact person from confirmed case of sars-cov-2 infection * medical staff exposed from confirmed case of sars-cov-2 infection in hospitals * persons exposed to sars-cov-2 in covid-19 outbreak situation with certain workplaces, religious groups, and military, etc. * subjects of study include both symptomatic and asymptomatic contacts.

inclusion criteria: * a contact person from confirmed case of sars-cov-2 infection * medical staff exposed from confirmed case of sars-cov-2 infection in hospitals * persons exposed to sars-cov-2 in covid-19 outbreak situation with certain workplaces, religious groups, and military, etc. * subjects of study include both symptomatic and asymptomatic contacts.

inclusion criteria: - a contact person from confirmed case of sars-cov-2 infection - medical staff exposed from confirmed case of sars-cov-2 infection in hospitals - persons exposed to sars-cov-2 in covid-19 outbreak situation with certain workplaces, religious groups, and military, etc. - subjects of study include both symptomatic and asymptomatic contacts.

inclusion criteria: - a contact person from confirmed case of sars-cov-2 infection - medical staff exposed from confirmed case of sars-cov-2 infection in hospitals - persons exposed to sars-cov-2 in covid-19 outbreak situation with certain workplaces, religious groups, and military, etc. - subjects of study include both symptomatic and asymptomatic contacts.