Saturday, 5 March 2016

Colombia - the sentinel chicken of Zika countries notes a microcephaly case...[UPDATED]

UPDATE #1: 06MAR2016 0750 AEST
UPDATE #2: 06MAR2016 2130 AEST
Declan Butler's piece for Nature [1] on the first confirmed microcephaly diagnosis from Colombia was my first read this Saturday morning. It's hard to know what to make of that diagnosis though, or of the two other congenital brain abnormalities mentioned. Will they usher in the next country to suffer a large wave of brain injury diagnoses or is that situation unique to Brazil? 

Another probable microcephaly diagnosis (I'm told it is a distinct diagnosis, different from the the confirmed case) in a 28 year old described in the media, was voluntarily aborted at 28 weeks gestation.[2,4]

It's unclear what trimester the mothers were infected in nor how that relates to when the first local ZIKV cases were first reported in Colombia in September 2015 - even that date is unlikely to be set in stone. Who knows how long ZIKV had been circulating in Colombia before it was first detected? 

Presumably RT-PCR was used to test the amniotic fluid sample in the second case but there was no foetal testing conducted as the remains were discarded - hence it being a probable case .[3,4] What sample(s) was tested or what type of test was used is unclear for the confirmed case. 

It is also unclear how many cases of microcephaly and congenital brain abnormalities are considered the norm in Colombia. I've been told around 140/year which is closer to the 150/year that Brazil initially reported - except that the population of Colombia is about is a quarter of Brazil's at 47 million,[5] with 204 million living in Brazil.[6] Colombians gave birth to approximately 0.8 million babies  in a July estimation, meaning that about 18 births per 100,000 were diagnosed with microcephaly.[5] In Brazil, nearly 3 million new lives appear each year giving a pre-ZIKV microcephaly diagnosis rate of about 5 per 100,000.[5,6] The Brazil "normal" figure was subsequently called into question, suggesting the number could be as high as a thousand per year.[2] This is a subject that remains unresolved and the outcome will likley have implications for Colombia's count too.

We'll await the publication pipeline for more answers.

References...
  1.  First Zika-linked birth defects detected in Colombia
    http://www.nature.com/news/first-zika-linked-birth-defects-detected-in-colombia-1.19502
  2. Microcephaly in northeastern Brazil: a review of 16 208 births between 2012 and 2015
    http://www.who.int/bulletin/online_first/16-170639.pdf
  3. Evidence Grows Linking Zika Virus to Birth Defect, Paralysis
    http://www.wsj.com/articles/evidence-zika-virus-can-cause-serious-complications-growing-1457110802
  4. Colombia reports 'probable' case of microcephaly in aborted fetus
    http://www.reuters.com/article/us-health-zika-colombia-idUSKCN0VX2S9
  5. https://www.cia.gov/library/publications/resources/the-world-factbook/geos/co.html
  6. https://www.cia.gov/library/publications/resources/the-world-factbook/geos/br.html
Update...
  1. New information received by email overnight detailed that 2 microcephaly diagnoses were described independently - a confirmed and a probable - and a rough idea of the number of microcephaly cases considered normal for Colombia.
  2. Population details and interpretation added for Colombia and Brazil