With around 3 million live births a year (roughly 8,500 live births average per day; 360 an hour ), there is likely to be a goodly number of twins when around 1.5% to 3.4% of live births result in twins of some type.[2,3]
I'm clearly no expert in the area of obstetrics, neonatology or congenital central nervous system disorders. But this finding, certainly not the first or only disease/healthy split between twins of this sort,[4,5,6,7] is fascinating.
To me, this finding highlights how rare the microcephaly and CNS disorder outcome seems to be after a suspected Zika virus infection of a mum at some point in her pregnancy. With so many births and just 1,300 M&CD diagnoses, its clearly nothing like as simplistic as "Zika virus infection while pregnant results in microcephaly".
The following tweets were a result of listening to Dr Celina Turchi Martelli, of the Brazilian Ministry of Health’s Fundação Oswaldo Cruz Foundation (FIOCRUZ)-Pernambuco, Brazil.
She gave a little insight into two case-control studies she is involved in, while speaking to the Cura Zika symposium hosted by The University of Pittsburgh.
@AndrewALover From aroudn 38min at https://t.co/3w20ZiN6Yp— Ian M Mackay, PhD (@MackayIM) May 5, 2016
if you want to get a better sense of it all. Thoughts? pic.twitter.com/3k33UcVjpF
In response to those, Dr Andrew Lover crunched some numbers and highlighted that those data, when viewed in isolation, suggest that a Zika virus infection alone is almost guaranteed to result in microcephaly.Prelim case-control study results— Ian M Mackay, PhD (@MackayIM) May 5, 2016
-#Zika infection detected in 12/23 - Odds Ratio 48
-Martelli #Zika pic.twitter.com/SctPplhRHp
But that is clearly not the case. Remember that total of 1,300 confirmed M&CD diagnoses amidst 8,500 live births a day? It was very probably not the intended meaning of Dr Martelli either.@MackayIM OR of 48 = 98% probability of MC given ZIKV(+); lower CI of 5.6 = 84.8% probability. Trimesters? DENV or CHIKV co-infection?— Andrew Lover (@AndrewALover) May 6, 2016
This all just exemplifies how confusing the Zika virus epidemic can be to the public, how complex finding a cause(s) to the M&CD surge will be and how much time may yet pass before we get anywhere near that goal.
It's all a bit confusing for scientists too!