El Niño, which is linked with the cycling of a Pacific Ocean circulation pattern known as the El Niño Southern Oscillation (ENSO), may produce extreme weather events, such as flooding and bushfire over many regions of the world. As a result, the impact of El Niño on population health is of great concern. Enormous economic losses and health burden caused by El Nino events have been documented.
Bacillary Dysentery, usually caused by Shigella bacteria, is a bacterial infection of the intestines that results in severe diarrhoea. The infection is spread from person to person via the oral-faecal route including food or drinking water. Epidemics are frequent in overcrowded populations with poor sanitation and low socioeconomic status, with most cases occurring in summer and autumn. Bacillary dysentery is still a public health problem in most developing countries. In China, for instance, there were approximately 500,000 notified cases of bacillary dysentery in 2005.
Changes in temperature, precipitation, humidity, and storm patterns, often related to the El Niño phenomenon, are associated with upsurges of water/food borne diseases such as dysentery, hepatitis A, typhoid, and cholera. ENSO has been found to be related to incidences of childhood diarrhoeal disease in Peru and cholera in Bangladesh. However, the relationship between El Nino events and dysentery, one of the most common infectious diseases during El Nino events, is far from clear.
An association between El Niño Southern Oscillation (ENSO) events and bacillary dysentery in a Chinese city has been reported recently. There is an indication that the number of dysentery cases is significantly negatively associated with the Southern Oscillation Index (SOI), the most commonly used index for ENSO events, with a time lag effect from 1 to 3 months (Figure 1). A strong negative SOI is associated with El Niño events. The results indicate that the lower the SOI the higher the incidence of bacillary dysentery. Thus the SOI could be used as an early indicator of the expected number of dysentery cases, as it is for other infectious diseases in China and Australia.
Challenges in examining the effects of El Niño on diarrhea including dysentery, are the reliance on the availability and quality of both disease surveillance data, and meteorological data, and the use of advanced statistical models. Time series analyses are recommended to evaluate the relationship between the disease outcome and El Niño events. In addition, other socioeconomic factors should also be taken into account in the study.
The study of the relationship between El Niño events and water/food borne diseases is significant for effective of disease prevention and control. El Niño can be predicted with enough lead time so that preventive and mitigate measures can be taken in anticipation of disease outbreaks.
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