I think it would be helpful if they medical people in the affected countries would take statistics on how many children were born to woman known to be infected with Zika and keep track of how many were babies were born with microcephaly vs. those who were not. If Zika really is involved then the ratio
#microcephaly & zika/ #no microcephaly & zika should be significantly different than the ratio #microcephaly & no Zika/#no microcephaly & no Zika.
I've seen in the news items of women who were tested for Zika after microcephaly, but that's just confirmation basis. Without the ability to compare the ratios I don't think it's clear that one can conclude that Zika causes microcephaly.
Does anyone know if those statistics have been published anywhere accessible? A google search on papers leads to the Elsevier paywall making the papers useless to me as I don't have an account with Elsevier.