Seasonal flu by ZIP code Influenza virus strikes communities in northern latitudes during winter, straining health care provision almost to the breaking point. Change in environmental humidity is a key driver, but many other seasonal and social factors contribute. Dalziel et al. obtained a geographical distribution of doctor visits for influenza-like illness for more than 600 U.S. cities (see the Perspective by Wallinga). Some ZIP codes regularly experienced sharply defined peaks of cases, or intense epidemics, and others showed a longer, more diffuse influenza season. The surges tended to occur in smaller cities with less residential density and lower household incomes. Larger, more densely populated cities had more-diffuse epidemics, presumably because of higher rates of personal contact, which makes influenza transmission less subject to climate variation. Science, this issue p. 75; see also p. 29 Seasonal flu epidemics are more diffuse in larger cities and more intense in smaller cities, where climate has a stronger influence on transmission. Influenza epidemics vary in intensity from year to year, driven by climatic conditions and by viral antigenic evolution. However, important spatial variation remains unexplained. Here we show predictable differences in influenza incidence among cities, driven by population size and structure. Weekly incidence data from 603 cities in the United States reveal that epidemics in smaller cities are focused on shorter periods of the influenza season, whereas in larger cities, incidence is more diffuse. Base transmission potential estimated from city-level incidence data is positively correlated with population size and with spatiotemporal organization in population density, indicating a milder response to climate forcing in metropolises. This suggests that urban centers incubate critical chains of transmission outside of peak climatic conditions, altering the spatiotemporal geometry of herd immunity.

中文翻译：

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城市化和湿度影响美国城市流感流行的强度

按邮政编码划分的季节性流感 流感病毒在冬季袭击北纬地区的社区，几乎使医疗保健供应紧张到了极限。环境湿度的变化是一个关键驱动因素，但许多其他季节性和社会因素也有影响。达尔齐尔等人。获得了美国 600 多个城市因流感样疾病就诊的地理分布（参见 Wallinga 的观点）。一些邮政编码经常出现明显的病例高峰或严重的流行病，而另一些邮政编码则表现出更长、更广泛的流感季节。激增往往发生在居住密度较低和家庭收入较低的小城市。更大、人口更稠密的城市有更广泛的流行病，大概是因为个人接触率更高，这使得流感传播较少受气候变化的影响。科学，这个问题 p。75; 另见第。29 季节性流感流行在大城市更为分散，在小城市更为严重，气候对传播的影响更大。受气候条件和病毒抗原进化的驱动，流感流行的强度每年都不同。然而，重要的空间变化仍然无法解释。在这里，我们展示了受人口规模和结构驱动的城市间流感发病率的可预测差异。来自美国 603 个城市的每周发病率数据显示，较小城市的流行集中在流感季节的较短时期，而在较大的城市，发病率更为分散。根据城市级发病率数据估计的基本传播潜力与人口规模和人口密度的时空组织呈正相关，表明大都市对气候强迫的反应较温和。这表明城市中心在高峰气候条件之外孵化了关键的传播链，改变了群体免疫的时空几何结构。