聚集性疫情是指在一个特定的地理位置或时期内，出現异常和相对不常见的疾病疫情[1]。通常情况下，当流行病学家意識到可能出現聚集性疫情時，他们会向当地的公共卫生部门报告[2]。如果聚集性疫情規模進一步擴大，此種情況可能被重新認定为疾病爆发。
Aggregations of relatively uncommon events or diseases in space and/or time in amounts that are believed or perceived to be greater than could be expected by chance. Putative disease clusters are often perceived to exist on the basis of anecdotal evidence, and much effort may be expended by epidemiologists and biostatisticians in assessing whether a true cluster of disease exists.