The reproductive number of Zika in municipalities of Antioquia, Colombia: stratifying the potential transmission of an ongoing epidemic

TL;DR

This study estimates and compares the basic reproductive number of Zika across municipalities in Antioquia, Colombia, highlighting areas with higher transmission potential to inform targeted surveillance and control efforts.

Contribution

It introduces a simple SIR model with implicit vector dynamics to estimate the reproductive number from regional case data, stratifying transmission risk at the municipal level.

Findings

15 municipalities had Ro>1 indicating high transmission potential

5 municipalities had Ro<1 but some risk of transmission later emerged

Surveillance should focus on municipalities with Ro>1 for effective control

Abstract

Introduction: Zika epidemic in America was declared a public health emergency of international concern after the rapid spread in the region. Stratification of the potential transmission of the disease is needed to address the efforts surveillance and disease control. The goal of this research is to compare the basic reproductive number of Zika in different municipalities, from an SIR model with implicit vector dynamics, based on the daily case reporting data of Antioquia, Colombia, the second most affected country after Brazil. Methods: An simple SIR model with implicit vector dynamics was derived and used. The approximate solution of the model in terms of individuals recovered in each time unit, allowed to obtain estimate of the model parameters including the basic reproduction number (Ro) and its 95% confidence intervals. These parameters were estimated via fitting the solution of the model to the daily reported cumulative cases data from the regional surveillance system. Results: Ro was estimated for 20 municipalities, all located at less than 2200 meters above sea level. From January to April 2016, between 17 and 347 cases were reported from these municipalities. Of these, 15 municipalities had a high potential for transmission (Ro>1) and 5 had less potential (Ro<1), although in 3 of these, transmission was later possible because its upper confidence interval of Ro was greater than one. Conclusion: Surveillance and control of Zika should be directed primarily to municipalities with Ro>1. Furthermore, strategies that will strengthen the detection and management of cases in the remaining municipalities should be beneficial to the whole Antioquia region.