Abstract
BackgroundHighly refined surveillance data on the 2009 A/H1N1 influenza pandemic are crucial to quantify the spatial and temporal characteristics of the pandemic. There is little information about the spatial-temporal dynamics of pandemic influenza in South America. Here we provide a quantitative description of the age-specific morbidity pandemic patterns across administrative areas of Peru.MethodsWe used daily cases of influenza-like-illness, tests for A/H1N1 influenza virus infections, and laboratory-confirmed A/H1N1 influenza cases reported to the epidemiological surveillance system of Peru's Ministry of Health from May 1 to December 31, 2009. We analyzed the geographic spread of the pandemic waves and their association with the winter school vacation period, demographic factors, and absolute humidity. We also estimated the reproduction number and quantified the association between the winter school vacation period and the age distribution of cases.ResultsThe national pandemic curve revealed a bimodal winter pandemic wave, with the first peak limited to school age children in the Lima metropolitan area, and the second peak more geographically widespread. The reproduction number was estimated at 1.6–2.2 for the Lima metropolitan area and 1.3–1.5 in the rest of Peru. We found a significant association between the timing of the school vacation period and changes in the age distribution of cases, while earlier pandemic onset was correlated with large population size. By contrast there was no association between pandemic dynamics and absolute humidity.ConclusionsOur results indicate substantial spatial variation in pandemic patterns across Peru, with two pandemic waves of varying timing and impact by age and region. Moreover, the Peru data suggest a hierarchical transmission pattern of pandemic influenza A/H1N1 driven by large population centers. The higher reproduction number of the first pandemic wave could be explained by high contact rates among school-age children, the age group most affected during this early wave.
Highlights
A few quantitative studies have started to shed light on the spatial, temporal, and age specific patterns of mortality and transmissibility levels of historical pandemic events [1], relatively little is known about the spatial-temporal patterns of the 2009 A/ H1N1 influenza pandemic at different spatial scales
The 2009 A/H1N1 influenza pandemic represents a unique opportunity to increase our understanding of the spatial-temporal diffusion patterns of pandemic influenza at different spatial scales, which is crucial for improving public health interventions against future influenza pandemics
Overall testing rates were higher in the greater Lima metropolitan area (86%) than in the rest of Peru (56%), and rates remained relatively stable over the entire pandemic period with an average weekly testing rate of 73.1%
Summary
A few quantitative studies have started to shed light on the spatial, temporal, and age specific patterns of mortality and transmissibility levels of historical pandemic events [1], relatively little is known about the spatial-temporal patterns of the 2009 A/ H1N1 influenza pandemic at different spatial scales. Peru is a interesting case study in this respect as it covers a variety of climatic zones associated with diverse influenza seasonal patterns [13] and public health authorities moved the national winter school vacation period by 2-weeks, in an attempt to mitigate the impact of the 2009 A/H1N1 pandemic. Whether the winter school vacation period had any impact on the transmission dynamics of the pandemic in Peru has yet to be evaluated, and this could provide insight into the role of school closures on control of future pandemics [8,9,14,15,16].
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