Estimates of Intrinsic Growth Rates and Basic Reproduction Number (R0) for the First Historical Zika Outbreak in Salta, Argentina

Abstract

Scopes and Objectives: After entering South America in May 2015 through northeast Brazil, the Zika virus spread to Argentina between April and June 2016 and reached Salta province the following year. We analyzed some aspects of the first historical outbreak of Zika that occurred in Salta, Argentina, in the year 2017. We obtained elementary estimates, such as the intrinsic growth rate of the cases accumulated in the first weeks of the outbreak, using expressions that relate it to the basic reproduction number thereof. Study design: Retrospective-descriptive studies and relational analysis. Place and Duration of Study: Department of Mathematics, Faculty of Exact Sciences and Faculty of Engineering. National University of Salta, Argentina, from September 2019 to June 2020. Methodology: Descriptive and relational analysis. Estimates of parameters and Simulation tests were also carried out in order to qualitatively describe the first Zika historical outbreak in Salta.  Results: Our study revealed that the Zika virus in the province of Salta mainly affects the localities of the departments of Or´an, General San Mart´ın, and Rivadavia, with infection forces α2017 ≈ 0.42 week-1 (SD 0.05) and α2017 ≈ 0.32 week-1 (SD 0.02) with the refined exponential model. On the other hand, we obtained estimates of the basic reproduction number R0 ≈ 1:105 95% CI[1:104 - 1:106] and R0 ≈ 1:111 95% CI[1:110 - 1:112].  Conclusion: Both the values of the estimates of the infection forces and R0 would seem to indicate that the first outbreak of Zika in Salta was of relatively low intensity and of short duration, coinciding with patterns generally present emerging diseases. We found practically no differences with the estimates provided by the two expressions of basic reproduction number used. Although the estimates slightly exceed the threshold value R0 = 1, with respect to other estimates, we consider them quite reasonable for the first historical outbreak occurred in Salta, since it was short-lived and of little intensity.