Apple and Google have teamed up to launch a mobile phone tool to follow the contacts of people infected with coronavirus. The technology is a form of “contact tracing,” a method used to identify people who may have had contact with infected individuals in an attempt to prevent additional spread of disease. Health officials say the method is an effective way to help slow the spread of highly contagious viruses. The current coronavirus, which is affecting much of the world, causes the disease COVID-19. Many carriers of the virus do not know they have it because they have no immediate signs of illness. They could be spreading the virus unknowingly. Contact tracing is a way to identify others who may have been infected.