1. World Health Organization. Coronavirus disease 2019 (COVID-19) situation report – 81. Geneva, Switzerland: World Health Organization; 2020. https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200410-sitrep-81-covid-19.pdf?sfvrsn=ca96eb84_2
2. CDC. Coronavirus disease 2019 (COVID-19): cases in U.S. Atlanta, GA: US Department of Health and Human Services, CDC; 2020. https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/cases-in-us.html
3. US Department of Homeland Security. Advisory memorandum on identification of essential critical infrastructure workers during COVID-19 response. Washington, DC: US Department of Homeland Security; 2020. https://www.cisa.gov/sites/default/files/publications/CISA_Guidance_on_the_Essential_Critical_Infrastructure_Workforce_Version_2.0_Updated.pdf
4. Guan WJ, Ni ZY, Hu Y, China Medical Treatment Expert Group for Covid-19. Clinical characteristics of coronavirus disease 2019 in China. N Engl J Med 2020;NEJMoa2002032. https://www.nejm.org/doi/10.1056/NEJMoa2002032
5. Livingston E, Bucher K. Coronavirus disease 2019 (COVID-19) in Italy. JAMA. Epub March 17, 2020. https://jamanetwork.com/journals/jama/fullarticle/2763401