It is, he says, both a sporadical and an epidemical disease, and when epidemical it is also contagious.
1650s (implied in sporadical), from Medieval Latin sporadicus "scattered," from Greek sporadikos "scattered," from sporas (genitive sporados) "scattered," from spora "a sowing" (see spore). Originally a medical term, "occurring in scattered instances;" the meaning "happening at intervals" is first recorded 1847. Related: Sporadically.
sporadic spo·rad·ic (spə-rād'ĭk, spô-) or spo·rad·i·cal (-ĭ-kəl)
Occurring at irregular intervals.
Occurring singly; not grouped.