Illness of a person onboard a vessel that may adversely affect the safety of a vessel or port facility is a hazardous condition per 33 CFR 160.216 and must be reported to the U.S. Coast Guard Captain of the Port (COTP). Cases of persons who exhibit symptoms consistent with COVID-19 must be reported to the COTP.
WORLD HEALTH ORGANIZATION GUIDANCE SPECIFIC TO MARITIME Operational considerations for managing COVID-19 cases/outbreak on board ships https://www.who.int/publications-detail/operational-considerations-for-managing-covid-19-cases-outbreak-on-board-ships