The reasons for the seasonality and annual changes in the impact of influenza epidemics remain poorly understood. We investigated the covariations between a major component of climate, namely the El Niño Southern Oscillation (ENSO), and indicators of the impact of influenza, as measured by morbidity, excess mortality and viral subtypes collected in France during the period 1971-2002. We show that both the circulating subtype and the magnitude of ENSO are associated with the impact of influenza epidemics. Recognition of this association could lead to better understanding of the mechanisms of emergence of influenza epidemics.

BACKGROUND: Seasonality characterizing influenza epidemics suggests susceptibility to climate variation. El Niño southern oscillation (ENSO), which involves two extreme events, El Niño and La Niña, is well-known for its large effects on inter-annual climate variability. The influence of ENSO on several diseases has been described.

OBJECTIVES: In this study, we attempt to analyze the possible influence of ENSO on the timing of the annual influenza activity peak using influenza-like illness report data in Japan during 1983-2007.

MATERIALS: Influenza surveillance data for 25 influenza epidemics, available under the National Epidemiological Surveillance of the Infectious Diseases, was used in this study. ENSO data were obtained from the Japan Meteorological Agency.

RESULTS: Influenza-like illness peak week varied largely during the study period, ranging between 4th and 11th weeks (middle of winter to early spring). The average of peak week during ENSO cycles (n = 11, average = 4.5 +/- 0.9) was significantly earlier than in non-ENSO years (n = 14, average = 7.6 +/- 2.9; P = 0.01), but there was no significant difference in the peak timing between hot (El Niño) and cold (La Niña) phases. Earlier peaks of influenza activity were observed in 16, out of 25, epidemics. These coincided with 10 (90.9%) out of 11 ENSO and 6 (85.7%) out of seven large-scale epidemics.

CONCLUSION: Influenza activity peak occurred earlier in years associated with ENSO and/or large scale epidemics.

深圳新闻网讯 记者11日从卫生部获悉，目前我国正处于流感流行高峰，南方省份流感活动水平继续呈上升趋势，北方省份流感活动水平在今年1月中旬达到高峰后，开始呈减弱态势。全国流感活动水平与近几年来的同期基本持平。

据专家研判，目前全球流感流行毒株以甲型H1N1流感、甲型H3N2亚型和乙型病毒为主。从总体上分析，全球流感活动水平明显低于2009年甲型H1N1流感全球大流行时期，与近几年流感流行强度相比基本持平。

统计显示，截至2月8日，2011年全国共有9个省份累计报告甲型H1N1流感死亡病例20例，低于2010年同期的140例。专家分析认为，由于甲型H1N1流感病毒本身未发生变异，世界卫生组织推荐的2010-2011季节性流感疫苗仍然有效，全国大规模暴发甲型H1N1流感的可能性小。

据介绍，卫生部门高度重视流感疫情防治工作，积极部署，流感监测哨点医院和网络实验室坚守岗位，各级医疗卫生部门认真开展流感疫情监测、防控和医疗救治等工作。

近期，卫生部门还将继续做好流感疫情监测和流感样重症病例的救治工作，同时鼓励重点人群和高危人群，尤其是托幼机构儿童和妊娠妇女接种季节性流感疫苗。