Johns Hopkins Bloomberg School of Public Health recently launched a free online course to train contact tracers in an effort to help slow the spread of COVID-19. From JHU's website: A long-used public health tool, contact tracing aims to break the chain of transmission of infectious diseases. The new Coursera class, "COVID-19 Contact Tracing," teaches the basics of interviewing people diagnosed with the virus, identifying their close contacts who might have been exposed, and providing…