There is still a possibility of transmission after the positive to negative test, but some infectious diseases lose their infectiousness, you need to consult your physician for details. Positive to negative there is still the possibility of infection, such as the new coronavirus infection, after treatment, the nucleic acid test became negative, but only the CT value of nucleic acid test has reached the negative index, do not rule out the possibility that the virus is still active, it can not completely rule out the possibility of infection, but only the viral load is relatively low. However, some infectious diseases become negative after treatment, such as tuberculosis, after treatment, tuberculosis mycobacteria test is negative, at the same time the tuberculosis foci in the lungs become old tuberculosis foci, it is generally not infectious, and the probability of resurgence is very low. Specific need to consult the doctor, subject to the doctor’s opinion.