本文描述了一个简单的数学模型，用于研究群体免疫对隐孢子虫水传和非水传暴发流行病学的影响。该模型在标准电子表格软件包上运行。从本质上讲，该模型将一个种群分为四组，每组都有不断增加的用水行为。在每个组中都有易感者和免疫者，在每个周期中，易感者转化为免疫者与他们的耗水量和“水传染性”有关。每个周期都有一部分免疫接种被易感者取代，以反映死亡和新生儿的替代情况。 每一个模型都被运行到免疫者和易感者之间的平衡状态，水的传染性会发生变化，从而使总人口中的免疫比例不同。人口免疫力的增加（由先前的水传播感染引起）对任何后续疫情期间与用水相关的感染相对风险有显著的负面影响。当免疫百分比从0%增加到20%时，这种影响最为显著。由于非水消耗导致的先前接触对由于暴发中的水而计算的相对风险没有影响。包括9个参考文献、图表。

This paper describes a simple mathematical model to investigate the impact of herd immunity on the epidemiology of waterborne and non-waterborne outbreaks of cryptosporidiosis. The model was run on a standard spreadsheet package. Essentially the model divided a population into four groups each with increasing water consumption behavior. Within each group there were susceptibles and immunes and for each cycle, susceptibles converted to immunes in relation to their water consumption and "water infectivity". Each cycle a proportion of the immunes were replaced by susceptibles to reflect deaths and replacement by new births. Each model was run to equilibrium between immunes and susceptibles with the water infectivity varied to make different proportions of the overall population immune. Increasing population immunity (caused by prior waterborne infection) has a marked negative impact on relative risk of infection associated with water consumption during any subsequent outbreak. The affect is most marked as the percentage immune increases from 0 to 20%. Prior exposure due to nonwater consumption had no effect on calculated relative risks due to water in outbreaks. Includes 9 references, figures.