The population suffered from periodic epidemics, including several serious outbreaks of bubonic plague. Major disease outbreaks or predicted pandemics can have similar effects. Cholera occurs as both outbreaks and chronically in certain areas. There have been five main cholera outbreaks and pandemics since 1825. Larger outbreaks known as pandemics are less frequent. There have been three major outbreaks of plague. Schools closed in many states in response to local flu outbreaks. The exact mechanism behind the seasonal nature of influenza outbreaks is unknown. They suffered through disease outbreaks and starvation. It can occur in outbreaks of disease. Mecca was regularly hit by cholera outbreaks. She died in 1927 during the influenza outbreaks of the 1920s. Fort Laramie marked the end of most cholera outbreaks. London had already suffered from a "series of debilitating cholera outbreaks". Eastern deciduous forests are subject to a number of serious insect and disease outbreaks.