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The geography of microcephaly in Brazil

Aedes aegypti or Yellow Fever mosquito

The Aedes aegypti or Yellow Fever mosquito is the sole vector for the transmission of chikungunya in the Americas at this time.

The number of reported cases of microcephaly in Brazil continues to increase. The geography of the reporting raises some questions about the outbreak in general, as well as any link to an infectious illness.

Brazil released the latest data on the number of microcephaly cases in that country since Oct. 22. Through Feb. 13, the Ministry of Health has received 5,280 reports, investigated 1,345 and discarded 837 as incorrectly diagnosed. The discard rate is 62.2 percent.

The majority of the reports of microcephaly are from three states in the northeast region of the country. Bahia, Paraíba and Pernambuco have reported 57.8 percent of all cases. Pernambuco has sent in 29.2 percent of all reports with the other two states at just over 14 percent each. No other state has reported over seven percent of the national total.


Bahia is the largest of these three states and has a population of over 15 million as of 2014. Pernambuco is next in size with about 9.3 million. Paraíba is the smallest in area and population with just under 4 million in population.

Look at the map. The states of Alagoas and Sergipe are surrounded by the three “outbreak” states. However, Alagoas has had 204 microcephaly reports and Sergipe 185.

Ceará and Piauí border two of the three “outbreak” states. Ceará has reported 287 instances of microcephaly while Piauí has reported 116.

Pernambuco  1,544  182  159  1,203
Paraíba  766  56  287  423
Bahia  744  107  54  583
Alagoas  204  25  89  90
Sergipe  185  0  8  177
Ceará  287  24  20  243
Piauí  116  30  12  74

The Brazilians are counting the “outbreak” numbers from Oct. 22, 2015. We are tracking data from Jan. 5 onward and now have a total of six reports from the Ministry of Health to work with.

At this point, for those reports of microcephaly that have been investigated, 62.2 percent have been discarded. If that ratio holds nationally, of the total of 5,280 reports in the period 10/22/2015 through 02/13/2016, 3,284 will be discarded and 1,996 accepted.

If infectious illness has a role in the confirmed cases of microcephaly, then why does Pernambuco have so many reports? Why do other, contiguous states, have fewer reports? Is this geographic distribution appear to be typical of the spread of an infectious illness?


  1. I can try if I can get to back reports from the PAHO. As of their 2/18 report, Brazil has 235 confirmed and 70,611 suspected Zika cases.

  2. Do we have localized ZIKV case numbers to run alongside that, over time?

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