Prognosis of a disease can be given by -

.the time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease in question is called incubation period.factors that determines it includes generation time,infective dose,poal of entry and individual susceptibility.it is helpful in tracing the source of infection,period of surveillance,immunization,identification of point source ot propagated epidemics,and also aids in prognosis.shoer the incubation period ,worser the prognosis would be,as in the case of tetanus,rabies etc. ref:park&;s textbook,ed 22,pg no 96