Table 1 Definitions

A disaster is a serious event that causes an ecological breakdown in the relation between humans and their environment on a scale that requires extraordinary efforts to allow the stricken community to cope, often with outside help or international aid [16, 17]. Disasters are clearly delineated into two major categories – those caused by natural phenomenon and those generated by humans. In natural disasters, a natural hazard impacts a population or area and may result in severe damage, destruction and increased morbidity and mortality that overwhelm local coping capacity [16].

Natural disasters can have an acute onset, such as geologic and climatic hazards (e.g. tsunamis, floods, and hurricanes), or slow onset such as drought and desertification. In complex emergencies (CEs), also called humanitarian emergencies, are defined as a humanitarian crisis in a country, region or society with total or considerable breakdown of authority resulting from internal or external conflict that requires an international response [31]. In CEs, mortality among the civilian population substantially increases above the population baseline mortality, either as a result of the direct effects of war, or indirectly through the increased prevalence of malnutrition and/or transmission of communicable diseases, especially if the latter result from deliberate political and military policies and strategies [22].

Epidemics, defined as an unusual increase in the number of cases of an acute infectious disease which already exists in the region or population concerned or the appearance of an infection previously absent from a region [10] can also be a disaster. For the purposes of this article, cases refer to mortality and not morbidity. Epidemics are differentiated from natural disasters, the latter being a physical or geological force of nature rather than biological. They can occur regularly, such as meningococcal meningitis in the meningitis belt of Africa. However, the occurrence of epidemics can increase and/or be exacerbated after natural disasters and CEs.