IS EL NINO-SOUTHERN OSCILLATION A DRIVING FORCE BEHIND SARS TRANSMISSION IN 2003?

Abstract

ISEE-259 Background: As a respiratory virus infection, the transmission of SARS coronavirus could be impacted by environmental factors including climatic variables such as rainfall and temperatures. Being a global scale pattern of climate variations, El Nino-Southern Oscillation, measured by the Southern Oscillation Index (SOI), might play an important role in the transmission of SARS because it affects most countries bordering on, or in the Pacific and Indian Oceans and accounts for up to 40% of temperatures and rainfall. A positive index of the SOI means low pressure and a tendency to greater rainfall, and a negative index indicates the opposite climate pattern. Methods: Daily suspected and probable SARS cases at both National and selected Provincial levels in China over period 21 April and 20 May, 2003 (Beijing and Tianjin Municipalities, Guangdong, Shanxi Provinces, and Inner Mongolia Autonomous Region) were retrieved from China Ministry of Health. Data of daily SARS cases from Hong Kong, Singapore (17 March to 20 May, 2003) and Canada (17 March to 18 June, 2003) were obtained from the WHO. Daily SOI data were provided by Australian Bureau of Meteorology. Spearman’s correlation analyses were conducted between daily SOI and SARS cases in various places of China, Hong Kong, Singapore and Canada over the study period, with lagged effect of 0 to 10 days. Results: There were medium to high reverse correlations between SOI and transmission of SARS in China (at both National and Provincial levels), Hong Kong, Singapore and Canada over the study period, with various lagged effect (4 to 9 days). This indicated the lower value of the SOI, the more daily cases of SARS. Discussion: To prevent further international spread of SARS and other infectious diseases, it is necessary to set up a possible early warning system, using a practical index which can be applied into larger geographic area. The use of the SOI provides a possible tool to achieve the goal. This is very important in SARS prediction and prevention, especially when several probable SARS cases appeared again in Singapore, Taiwan, China and Philippines in late 2003 and early 2004.