Viruses 10 (12): 683, 2018. doi: 10.3390 / v10120683 Diagnosis of Viral Infections Some viral disorders can be diagnosed as follows: Clinically (ie, diagnosis based on well-known patient symptoms, eg, measles, rubella, roseola infantum, erythema infectiosum, and chickenpox) Epidemiologically (ie, diagnosis based on case definition during epidemic outbreaks, eg, influenza, norovirus, and mumps) Definitive laboratory diagnosis is necessary mainly when specific treatment may be helpful or when the agent may be a public health threat (eg, HIV).