Table 3

Clinical classification of microcephaly cases: comparing earlier years (pre-Zika) with later years (during and after Zika)

All registries, excluding Brazil* Brazil
Pre ZikaZikaComparison prevalence
Pre Zika
Pre ZikaZikaComparison prevalence
Pre Zika
Birth years2010–2015†2016–2017‡2010–20142015–2017
Population births2 339 8981 161 85414 564 1038 799 003
Cases (%)Prev. per 10 000Cases (%)Prev. per 10 000Cases (%)Prev. per 10 000Cases (%)Prev. per 10 000
A1.1. Chromosomal syndromes42 (8)0.1842 (6)0.36p<0.00216 (2)0.0120 (0.4)0.02p=0.037
A1.2. Genetic syndromes excl chromosomal37 (7)0.1626 (4)0.22p=0.18223 (3)0.0234 (1)0.04p=0.001
A2. Infectious embryopathies not incl Zika virus10 (2)0.0413 (2)0.11p=0.025Information not provided
Zika virus0 (0)0.0029 (4)0.25
B. Polymalformed without syndrome diagnosis220 (41)0.94148 (22)1.27p=0.005258 (30)0.18531 (12)0.60p<0.001
C. Microcephaly with malformations of neural origin25 (5)0.1118 (3)0.15p=0.25786 (10)0.0695 (2)0.11p<0.001
Isolated microcephaly209 (38)0.89411 (60)3.54p<0.001469 (55)0.323907 (85)4.44p<0.001
Total microcephaly543 (100)2.32687 (100)5.91p<0.001852 (100)0.584588 (100)5.21p<0.001
  • *Mexico Nuevo León contributed data for 2015–2017 only, Chile National for 2016–2017 only and Colombia Bogota for 2014–2017 only.

  • †Total microcephaly cases, 543, for 2010–2015 excludes 11 cases from Nicaragua as case-level data not available.

  • ‡Total microcephaly cases, 687, for 2016–2017 excludes 30 cases from Nicaragua in 2016–2017 and 78 cases from Argentina in 2017 as case-level data not available for these years.