Tehran University of Medical Sciences Journal of Biostatistics and Epidemiology 2383-4196 7 2 2021 07 04 221 223 Yousef Alimohamadi Pars Advanced and Minimally Invasive Medical Manners Research Center, Pars Hospital, Iran University of Medical Sciences, Tehran, Iran. Mojtaba Sepandi Health Research Center, Life Style Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran. Taher Teymouri Rasool Akram Hospital, Iran University of Medical Sciences, Tehran, Iran Hadiseh Hosamirudsari Department of Infectious Diseases, Baharloo Hospital, Railway Square, Tehran University of Medical Sciences, Tehran, Iran. 2021 04 05 2021 04 09 Introduction: Epidemic curves are a type of time series data consisting of the number of events that occur over a period of time. The time unit in this data can be a day, a week, or a month, etc.  Methods: In the current letter, the authors tried to explain the growth factor and its effect on epidemic curves by using some literature.  Results: In the outbreaks setting, the number of cases can increase with different patterns. When the number of cases is increasing exponentially, it means that the number of cases is increasing at a certain speed, which is determined by a factor called an exponential growth factor. When this factor is greater than one, it means that the cases are increasing exponentially, and when this coefficient is equal to 1, it means that we have reached an inflection point that we will face a change in the growth rate of the cases.  Conclusion: Some factors such as reducing the contact between infected and healthy people, run the social distancing program, and so on can have an effective role in decreasing epidemic growth factor and controlling the epidemic. https://jbe.tums.ac.ir/index.php/jbe/article/view/468