Mathematical, Computational and Modeling Sciences Center, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, USA.
Proc Biol Sci. 2010 Jun 22;277(1689):1857-66. doi: 10.1098/rspb.2009.1897. Epub 2010 Feb 11.
The transmission dynamics of influenza in tropical regions are poorly understood. Here we explore geographical variations in the reproduction number of influenza across equatorial, tropical and subtropical areas of Brazil, based on the analysis of weekly pneumonia and influenza (P&I) mortality time series in 27 states. The reproduction number (R) was low on average in Brazil (mean = 1.03 (95% CI 1.02-1.04), assuming a serial interval of 3 days). Estimates of the reproduction number were slightly lower for Brazil than for the USA or France (difference in mean R = 0.08, p < 0.01) and displayed less between-year variation (p < 0.001). Our findings suggest a weak gradient in the reproduction number with population size, where R increases from low population in the North to high population in the South of Brazil. Our low estimates of the reproduction number suggest that influenza population immunity could be high on average in Brazil, potentially resulting in increased viral genetic diversity and rate of emergence of new variants. Additional epidemiological and genetic studies are warranted to further characterize the dynamics of influenza in the tropics and refine our understanding of the global circulation of influenza viruses.
流感在热带地区的传播动态尚未得到充分了解。本研究基于对巴西赤道、热带和亚热带地区 27 个州每周肺炎和流感（P&I）死亡率时间序列的分析，探讨了流感繁殖数的地理差异。巴西的繁殖数（R）平均值较低（平均值=1.03（95%置信区间为 1.02-1.04），假设序列间隔为 3 天）。与美国或法国相比，巴西的繁殖数估计值略低（平均 R 的差异=0.08，p<0.01），且年度间的变化较小（p<0.001）。我们的研究结果表明，繁殖数与人口规模呈弱梯度关系，即 R 从巴西北部的低人口地区增加到南部的高人口地区。我们对繁殖数的低估计表明，巴西的流感人群免疫力可能普遍较高，这可能导致病毒遗传多样性增加和新变体出现的速度加快。需要进行更多的流行病学和遗传学研究，以进一步描述热带地区流感的动态，并深入了解流感病毒的全球传播。
