Zika virus – Incidence and trends
Since the last epidemiological update (31 March 2016), one additional country, Saint Lucia reported its first autochthonous (locally-acquired) confirmed cases of Zika virus infection on 7 April. This brings the total to 34 countries and territories reporting local, vector-borne transmission of Zika virus in the Region of the Americas since 2015 (Figure 1).
Regional and national trends reveal important shifts in circulation at sub-national levels. This is illustrated with data from Colombia which show some sub-national areas experiencing an increase in reported Zika cases, while in others, the number of cases are decreasing (Figure 2).
Trends in reporting of acute flaccid paralysis (AFP), suspected measles /rubella and arboviruses cases (dengue, chikungunya and Zika virus) in Colombia Before the introduction of Zika virus to the Region of the Americas, outbreaks of dengue and chikungunya had been registered in Colombia. Compared to 2013, Colombia experienced a large outbreak of dengue which started in August 2014 and peaked in April 2015. An outbreak of Chikungunya (55,000 cases) also began at the same time in 2014 mirroring the dengue epidemic curve (65,000 cases). With the introduction of Zika virus in August 2015, the trends of both arboviruses (dengue and chikungunya) started increasing simultaneously. Comparing the dynamics of dengue, chikungunya, and Zika virus with the monthly reported cases of acute flaccid paralysis (AFP), a temporal correlation is observed between an increase in APF cases and the start of the Zika virus outbreak (Figure 3).
In September 2015, when an imported measles case was confirmed in Colombia, surveillance activities for the disease were enhanced. Following this importation, an excess of suspected measles and rubella cases were identified from September through November 2015 (Figure 4).
This peak coincides with the increase in notification of Zika virus cases in Colombia. Of note, there have been peaks of suspected measles-rubella cases in the months of September of 2013 and 2014. According to routine case investigation procedures, both measles and rubella were ruled out in all these cases. In addition, dengue was also ruled out in few reported cases.
These observations highlight the need for having strong surveillance systems for measles-rubella and polio (eliminated diseases) and underscore the importance of integrated analysis of different surveillance systems to better understand the emergence of Zika virus.