Specifically, the warming of the Pacific Ocean during an El Ni o causes changes in cloud cover and evaporation levels that produce an increased heat flux in this area. The effects are further influenced by regional climate variables. Other factors affecting climate in this area are the melting of the snow pack in the Himalayas. This is known to affect the monsoons, precipitation levels and river flooding. There are also annual or seasonal influences on climate.
Cholera is dose dependent.
Therefore the disease can be prevented by avoiding water sources where the level of bacteria present exceed a certain threshold, or by removing the bacteria from the water. They used sophisticated mathematical modelling methods that enabled them to test several hypotheses concerning the factors that are potentially involved. These researchers used three inter-related climate variables from remote sensing data to compute global correlational maps. They found consistent lag times between peaks in the data and records of cholera outbreaks. The lag time varied with the intensity of ENSO effects as well, which also affected the intensity of the outbreak.