The appearance of the coronavirus (COVID-19) in late 2019 has dominated the news in the last few months as it developed into a pandemic. In many mathematics and physics classrooms, instructors are using the time series of the number of cases to show exponential growth of the infection. In this manuscript we propose a simple diffusion process as the mode of spreading infections. This model is less sophisticated than other models in the literature, but it can capture the exponential growth and it can explain it in terms of mobility (diffusion constant), population density, and probability of transmission. Students can change the parameters and determine the growth rate and predict the total number of cases as a function of time. Students are also given the opportunity to add other factors that are not considered in the simple diffusion model.

中文翻译：

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扩散作为病毒感染传播的第一个模型

冠状病毒 (COVID-19) 在 2019 年末的出现在过去几个月中占据了新闻的主导地位，因为它已经发展成为大流行病。在许多数学和物理课堂中，教师正在使用病例数的时间序列来显示感染的指数增长。在这份手稿中，我们提出了一个简单的扩散过程作为传播感染的模式。该模型不如文献中的其他模型复杂，但它可以捕捉指数增长，并且可以从流动性（扩散常数）、人口密度和传播概率方面对其进行解释。学生可以更改参数并确定增长率并预测作为时间函数的病例总数。学生还有机会添加在简单扩散模型中未考虑的其他因素。