Organon §241

To find the remedy that is best for almost all patients in an epidemic who are not suffering from developed psora, discover the symptom complex common to all.

Those epidemics of intermittent fever that occur outside areas where such fevers are endemic have the nature of chronic diseases composed of single, acute attacks. Each epidemic has its own self-same character which is common to all of the individuals who are taken ill. If the character of the epidemic disease is discovered according to the symptom complex common to all the patients [i.e. , the genus epidemicus], this will point to the homeopathically fitting (specific) remedy for the totality of the cases. This remedy almost always helps in those patients who enjoyed tolerably good health before the epidemic, that is, who were not chronically sick with developed psora.