Mulatti P, Kitron U, Mannelli A, Ferré N, Marangona S
Centro Regionale per l'Epidemiologia Veterinaria, Istituto Zooprofilattico Sperimentale delle Venezie, Viale dell'Università 10, 35020 Legnaro PD, Italy.
Avian Dis. 2007 Mar;51(1 Suppl):421-4. doi: 10.1637/7549-033106R.1.
The effect of proximity on infected premises was evaluated during the highly pathogenic avian influenza (HPAI) epidemic that struck northern Italy in 1999-2000 by quantifying the spatial and temporal clustering of cases. The epidemic was caused by an H7N1 subtype of type A influenza virus that originated from a low-pathogenic AI virus that spread among poultry farms in northeastern Italy in 1999 and eventually became virulent by mutation. More than 90% of 413 infected premises were located in Lombardy and Veneto regions; of 382 outbreaks, 60% occurred in the Lombardy region and 40% in the Veneto region. Global and local spatial statistics were used to estimate the location and degree of clustering of cases with respect to the population at risk. Outbreaks were spatially clustered primarily in Lombardy, with a large cluster in Brescia province and another in Mantua province, on the border of Veneto. Time series analysis was used to assess the temporal clustering of outbreaks. Temporal aggregation increased during the first 5 wk and decreased thereafter (probably as a result of eradication measures enforced in the Veneto region). Spatio-temporal clustering was assessed considering the Temporal Risk Window (TRW), the time period during which premises remain infectious and infection can spread to neighboring premises. The clustering pattern was similar to the one detected when considering spatial clustering (i.e., the larger clusters were identified in the Brescia and Mantua provinces of Lombardy). These results highlight the role of proximity in the spread of AI virus and, when considering the TRW, indicate the possible direction of virus spread.
在1999 - 2000年袭击意大利北部的高致病性禽流感（HPAI）疫情期间，通过量化病例的空间和时间聚集情况，评估了临近感染场所对疫情的影响。此次疫情由甲型流感病毒H7N1亚型引起，该亚型起源于一种低致病性禽流感病毒，1999年在意大利东北部的家禽养殖场中传播，最终通过变异变得具有毒性。413个感染场所中超过90%位于伦巴第大区和威尼托大区；在382起疫情中，60%发生在伦巴第大区，40%发生在威尼托大区。采用全局和局部空间统计方法来估计病例相对于高危人群的聚集位置和程度。疫情在空间上主要聚集在伦巴第大区，在布雷西亚省有一个大的聚集区，在与威尼托大区接壤的曼托瓦省还有一个。采用时间序列分析来评估疫情的时间聚集情况。在前5周内时间聚集性增加，之后下降（可能是威尼托大区实施根除措施的结果）。考虑到时间风险窗口（TRW），即场所保持传染性且感染可传播至相邻场所的时间段，对时空聚集情况进行了评估。聚集模式与考虑空间聚集时检测到的模式相似（即在伦巴第大区的布雷西亚省和曼托瓦省发现了较大的聚集区）。这些结果突出了临近因素在禽流感病毒传播中的作用，并且在考虑时间风险窗口时，表明了病毒传播的可能方向。
