Why are there frequent outbreaks of infectious diseases after entering the 21st century, tell us your opinion?

After entering the 21st century, natural disasters and localized wars have led to frequent outbreaks of infectious diseases: excerpt People often misunderstand the relationship between natural disasters and infectious diseases. People associate infectious diseases with corpses, and thus worry that "after a big disaster, there will be a big epidemic". However, the risk of post-disaster outbreaks is primarily associated with population movement. The availability of clean water and sanitation, the density of the population, the health status of the population itself, and the availability of appropriate health care all interact with the local epidemic ecology and ultimately influence the risk of transmissible disease outbreaks and the mortality rate of infected populations. Here we summarize the risk factors that trigger epidemics after a disaster, assess the potential for serious outbreaks, and prioritize post-disaster epidemic prevention efforts. Natural disasters are calamities caused by atmospheric, geological or hydrological factors, including earthquakes, volcanic eruptions, mudslides, tsunamis, floods and droughts. Natural disasters can erupt suddenly or be slow-onset and have significant safety and health, social and economic impacts. Over the past two decades, natural disasters have killed millions of people globally and affected the lives of more than a billion others, causing immeasurable economic losses (1). Developing countries that are underfunded, have weak infrastructure, and lack pre-disaster emergency response programs tend to be more traumatized in disasters. Most deaths associated with natural disasters, especially those caused by sudden-onset disasters, come from smashing and crushing injuries, or drowning. In contrast, deaths from infectious diseases are less common after disasters. Corpses and Disease Large numbers of deaths due to disasters tend to heighten concerns about disease outbreaks (2), yet in fact, there is no evidence that large numbers of corpses lead to post-disaster infectious disease outbreaks (3). When deaths are caused by the natural disaster itself, there is no risk of causing an infectious disease outbreak for the survivors (4). The risk of an outbreak of infectious disease due to corpses exists only in certain situations that require special precautions, such as cholera (5) or hemorrhagic fever. Please refer to Table I in the Appendix for the principles of disposal of dead bodies. Regardless of the facts, the likelihood of post-disaster outbreaks is often exaggerated by health authorities and the media. Despite attempts by scientists to clarify these unfounded misconceptions, the 'threat of an impending epidemic' is a recurring theme in media coverage of disaster areas. The primary issue: population movement The risk of spreading infectious diseases after a disaster is primarily related to the number and characteristics of the people moving, including the availability of potable water and available latrines in the immediate vicinity, the nutritional status of the moving population, the proportion of the population immunized against infectious diseases such as measles, and the availability of health care services, to name a few. (8) The risk of outbreaks of epidemics is lower in populations affected by natural disasters than in populations affected by wars and conflicts, where 2/3 of deaths may be caused by epidemics. (9) Malnutrition increases the risk of dying from epidemics, which is more prevalent in war conflicts, especially when populations move as a result of prolonged fighting. (10) Outbreaks of epidemics following floods (11) are better documented than conditions following earthquakes, volcanic eruptions, and tsunamis (12). In general, however, those natural disasters (of any type) that do not result in population displacement are hardly ever followed by epidemic outbreaks. (8) The historical infrequency of large-scale population movements due to natural disasters is likely one of the reasons why large-scale outbreaks of epidemics have been infrequent in human history.(8) This explains why the risk of outbreaks of epidemics varies after different types of disasters. Risk Factors for Infectious Disease Transmission In order to effectively assist disaster-affected populations, we need to accurately assess the risk of epidemics. Based on the risk assessment, we can prioritize the distribution of relief funds. A systematic and comprehensive assessment of outbreak risk involves identifying the following: endemic and epidemic diseases that are common in the affected area; and the living conditions of the affected population. The living conditions of the affected population, including population size, size, location, and density; the availability of clean water and adequate sanitation; the basic nutritional status and vaccination rates of the affected population; and the status of health care and case management. The following types of communicable diseases are associated with populations displaced by natural disasters. The following diseases should be treated with caution when conducting post-disaster risk assessments. Water-related infectious diseases Epidemics associated with crowded populations Vector-borne infectious diseases Other diseases associated with natural disasters Diseases caused by the disruption of disaster supplies Water-related infectious diseases Safe and clean water sources can be destroyed by a natural disaster. Outbreaks of diarrhea-like illnesses can occur when drinking water is contaminated, and such outbreaks have been reported following floods and associated displacement. In an outbreak following floods in Bangladesh in 2004, more than 17,000 cases presented with diarrhea; Vibrio cholerae (serotypes Ogawa and Inaba), and toxigenic Escherichia coli have all been detected (13) A major cholera outbreak in West Bengal in 1998 (serotype Ogawa, more than 16,000 cases) is also thought to be related to previous floods (14); and the floods in Mozambique from January 2000 to March floods in Mozambique also led to an increase in diarrhea cases. In a large-scale study conducted in Indonesia in 1992-1993, flooding was identified as an important risk factor for diarrheal epizootics caused by Salmonella paratyphi A (16). In another Indonesian study evaluating risk factors for Cryptosporidium minutum infection in 2001-2003, case patients were more than four times as likely to get the disease after exposure to flooding compared with controls (17).