Tuesday 12 April 2016

A line is about to be crossed...

Colombia has already reported over 30 cases of congenital foetal anomalies in 2016. This is not outside the "normal range" for such disease - at the moment.[4]

From [4].
However, there are over 1,500 hundred laboratory confirmed Zika virus infected pregnant women in Colombia -  over 10,200 if you don't worry about laboratory confirmation.

Why am I telling you this?

Because a line in time is about to be crossed.

Brazil first reported reported positive (but unconfirmed) laboratory tests for Zika virus disease on 29th April 2015. Brazil then started to report a rise in foetal anomalies (an initial 141), in the form of microcephaly on 30th October 2015. This was 184 days - or about 6 months later.[1]

Zika virus was first confirmed in Colombia on 16th October 2015. Today, 12th of April 2016, is 179 days, or about 6 months later.[1] Colombia is currently carrying the next biggest load of Zika virus disease cases, after Brazil.[6]

It would be incredibly dense of me to suggest that at exactly 184 days a whole lot of babies with microcephaly and a host of brain injuries will suddenly be born. However, we are about to cross a significant line after which we may see a steady and continuous increase in birth defects, well above the expected averages, accruing in Colombia. This is no proof, but will greatly add weight to the case for Zika virus infection causing such anomalies if it happens. 

Growing Zika virus case number trends in dark blue
From PAHO-WHO [5]
It would also be stupid of me to suggest that the rate or the total numbers of diagnoses will be directly comparable to those in Brazil. Because we have very little testing data to use to compare between Colombia (lots) and Brazil (hardly any as can be seen by lack of Brazil graphics in recent PAHO-WHO report[5]), we don't really know how well Zika spread has been captured. Is Zika virus focal, widespread, ongoing (see map for Colombia above that suggest it is), decreasing, what was it when the first laboratory confirmation occurred, what is like now...? 

We also don't know how closely the first reported detections of Zika virus correlates with the first actual cases of infection in the two countries nor who fast new cases spread.

Then, there's that hint that perhaps there is as much as a 2 month delay in reporting Zika virus positives in Colombia; factor that into the timeline above.[3]

But from here on in, watch Colombia closely.

  1. http://who.int/bulletin/online_first/16-171082/en/
  2. http://who.int/…/zika-vir…/zika-historical-distribution.pdf
  3. http://virologydownunder.blogspot.com.au/2016/04/colombiano-recent-confirmed-zika-virus.html
  4. http://virologydownunder.blogspot.com.au/2016/04/colombia-zika-virus-report-week-no-13.html
  5. http://www.paho.org/hq/index.php?option=com_content&view=article&id=11599&Itemid=41691&lang=en
  6. http://www.nature.com/news/first-zika-linked-birth-defects-detected-in-colombia-1.19502

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