The decision to shorten the quarantine to six days, sources said, is based upon expert research and data — including the league’s own — that shows no one with a cycle threshold (CT) over 35 has shown to be infectious again after five or six days, sources said. CT measures how many times a test has to cycle to find the virus in an individual. For example, a 35 CT is fainter than a 20 CT. The NBA and NBPA has relied on data from its own infectious disease experts, the CDC and models and research in the United Kingdom.