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. 2018 Dec 27;18(1):695.
doi: 10.1186/s12879-018-3484-z.

Seasonal dynamics of influenza in Brazil: the latitude effect

Alexandra Almeida  1   2 , Cláudia Codeço  3 , Paula M Luz  4
Affiliations

Seasonal dynamics of influenza in Brazil: the latitude effect

Alexandra Almeida et al. BMC Infect Dis. .

Erratum in

Abstract

Background: Influenza is a global transmissible disease. Its dynamics is far better understood in temperate climates than in the tropics. We aim to close this knowledge gap between tropical and temperate regions by showing how the influenza seasonality evolves in Brazil, a tropical country that encompasses a wide range of latitudes and six climatic sub-types.

Methods: We analyzed a state-level, weekly Syndrome of Acute Respiratory Disease (SARI) incidence data ranging from 2010 to 2016. We combined two techniques hierarchically: first the wavelet decomposition technique to detect annual periodicity and then circular statistics to describe seasonal measures of the periodic states.

Results: We found significant annual periodicity in 44% of the states. For these, we calculated several seasonal measures such as the center of gravity or mean timing of activity. The relationship between the seasonal signatures and latitude was clear and statistically significant. States with seasonal signature are clustered along the coast. Most Amazonian and Central West states exhibit no seasonal behavior. Among the seasonal states, influenza starts in Northeast region, spreading southbound.

Conclusions: Our study advances the comprehension of influenza seasonality in tropical areas and could be used to design more effective prevention and control strategies.

Keywords: Circular; Influenza; Seasonality; Wavelet decomposition.

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Conflict of interest statement

Ethics approval and consent to participate

Ethical approval was not required for this study as it uses secondary data.

Consent for publication

This study does not include any identifying data and thus does not require a consent to publish.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Distribution of incidence per 100,000 inhabitants (on the left), and peak-week by year (on the right) for all Brazilian states and FD, ordered by capital latitude, north on top
Fig. 2
Fig. 2
On the left, the wavelet power spectrum where: (i) values increase from blue to red, (ii) white contour lines indicates the 95% confidence interval and (iii) shaded regions on both ends delimiting the cone of influence. On the right, the graphic represents the average wavelet power over time, where dots indicate significant periods at different significance levels. In the top line, the results of Amapá, a northern state and; in the bottom, the Paraná wavelet results, in the south of the country
Fig. 3
Fig. 3
States classified as annual-seasonal (in orange)
Fig. 4
Fig. 4
Rose diagram for SARI incidence in Rio Grande do Sul, Brasília (Federal District) and Amazonas (from left to right). The von Mises adjusted probability density function in dashed blue ellipse. The year progresses counterclockwise
Fig. 5
Fig. 5
Annual mean activity (left), mean timing of activity/center of gravity (right) by latitude. Results for states with annual seasonality in coral, and non seasonal in gray
See this image and copyright information in PMC

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