Zika in Colombia: Transitioning into endemicity

Earlier this week, Colombia declared that its Zika outbreak was officially over… I, however, am skeptical – as are others.

Based off of the weekly epidemiological data published by the Instituto Nacional de Salud (INS), it seems too early to say whether or not we’ve exited the “epidemic” phase and entered the “endemic” phase. Though the epidemic curve shown here (click here for high-resolution image) certainly indicates that the outbreak is waning (as all outbreaks tend to eventually do!), any sort of formal statement is – in my opinion – premature.

Given that endemicity is expected in Colombia (though the degree to which it’ll occur is currently unknown), it’s unclear if we’ll ever see prolonged stretches of “zero incidence”. However, in order to claim that Zika in Colombia has transitioned from an epidemic to an endemic state, I personally think we need to see two serial intervals (i.e. 3 – 7 weeks) of low-level incidence with statistically insignificant week-to-week variation.

What will “low-level incidence” mean with respect to Zika in Colombia? For now, it’s unclear. But I plan to continue updating the epidemic curve to keep tabs on what is likely to be a delicate transition. Stay tuned!