Diagnosing and treating viral infections. One example is a method of diagnosing absence of severe acute respiratory syndrome 2 (SARS-CoV-2), the method including: isolating a human in a covid-free environment for an isolation period; performing measurements of a core temperature during the isolation period; and if each of the measurements of the core temperature indicate a lack of fever, declaring the human free of SARS-CoV-2. Another example is a method including treating coronavirus in a human by: receiving a core temperature measurement; receiving a test result regarding the SARS-CoV-2 virus; responsive to the human having both fever and the presence of the SARS-CoV-2 virus, submerging the trunk and the legs of the human in water with a surfactant, and the human at least partially submerged for a treatment period of at least three hours; and controlling a temperature of the water during the treatment period.