Is there an outbreak of microcephaly in Brazil? That is one of the first questions that ought to be asked when examining the topic of the potential effects of a prenatal Zika viral infection. Without knowing the preexisting rates of this serious yet usually rare birth defect, any recent change is impossible to detect. Unfortunately, data from public health authorities and medical educators is so varied that a conclusion may not be possible.
Each piece of data below will have a citation number, displayed in bold red, which refers to an ordered list at the bottom of this piece.
These tables use a variety of different sources with differing microcelphaly incidence rates to predict the “normal” number of microcephaly cases for both the United States and Brazil. [1/30/2016 7:22 pm – this paragraph added for clarification.]
|Births|| 2,953,597|| 3,988,076|
|Brazil, PER 10,000 ||0.5||148|
|CDC A, PER 10,000 ||1.0||295|
|CDC B, PER 10,000 ||2.0||591|
|ECLAMC, PER 10,000 ||1.98||585|
|CDC C, PER 10,000 ||591||2.0||798|
|CDC D, PER 10,000 ||3,544||12.0||4,786|
|Virginia DoH A, PER 10,000 ||1,181||4||1,595|
|Virginia DoH B, PER 10,000 ||1,772||6||2,393|
|Cleveland Clinic A, PER 10,000 ||347||1.18||469|
|Cleveland Clinic B, PER 10,000 ||476||1.61||643|
|Handbook of Toxicologic Pathology A, PER 1,000 ||1,772||0.6||2,393|
|Handbook of Toxicologic Pathology B, PER 1,000 ||4,726||1.6||6,381|
The second table uses the above data from the United States, and its application to Brazil, to show the means and medians.
I discarded the data from the highest incidence, 12:10,000 and the lowest, 0.6:1,000 before calculating. [1/30/2016 7:22 pm – I have corrected the mean and median calculations. I believe that removing the two highest values, CDC D and Handbook B, provides better data for these statistical values. I have also corrected a typo by changing the second Handbook entry to B from a duplicate A.]
In a Jan. 26 article in Nature, Declan Butler explores the possibility that the increase in reported microcephaly cases in Brazil is unrelated to an outbreak of Zika viral illness and may even be non-existent. The article, titled Zika virus: Brazil’s surge in small-headed babies questioned by report, is based upon a report from the Latin American Collaborative Study of Congenital Malformations (ECLAMC) .
In the article, Butler reports that as of Jan. 27, Brazil had “4,180 suspected cases of microcephaly recorded since October.” The government had examined 732 of those, and had rejected 462, 63 percent, as false diagnoses. While the ratio of false diagnoses of 462:732 is unlikely to be the final result, it provides an additional set of data that can be analyzed in a limited way.
Using the 4,180 suspected cases as a starting point, the analysis suggests that 1,547 cases will be found to be properly diagnosed as microcephaly. That number is very uncertain but it is useful. If incidence rates other than those from the Brazilian government and the rates labelled CDC A and CDC B are used, 1,547 begins to look a lot like a normal number of cases.
ECLAMC notes in its report that the Brazilian authorities are using an unproven criteria for microcephaly. The government has changed the diagnostic criteria to reflect that all children with a head circumference of less than 33 cm. should be reported as a case of microcephaly.
Normal head circumference is known to vary by ethnicity.  Newborns in the United States have been found to have a larger head, on average, then those in the Third World. It is also noted that an exam and measurement of the skulls of a newborn’s parents is also warranted as the family may just be expressing a trait for a smaller than average skull.
More than one study has noted that the WHO charts vary from those produced by the CDC. “For children in industrial countries, the mean OFC is larger than that indicated in the WHO standard values, which are based on measurements taken from about 8500 children in Brazil, Ghana, India, Oman, and the USA.”  OFC is the abbreviation for occipital-frontal circumference.
Data exists that suggests that the number of confirmed cases of microcephaly in Brazil will be far lower than the number of reports. In addition, the actual number of cases of microcephaly per year in Brazil prior to the arrival of the Zika viral illness is less clear than it might be. It is impossible to draw a sound conclusion that the Zika outbreak has or has not added to the number of cases of microcephaly in Brazil.
The data is suggestive that the number of microcephaly cases will range, in a given 12 months, from normal to two or three times normal. It remains an issue of great concern but the hype seems to have far exceeded the threat.
Citations and Sources
- CIA World Factbook 2015 estimate
- U.S. National Vital Statistics Report Births:Final Data for 2014
- Schuler-Faccini L, Ribeiro EM, Feitosa IM, et al. Possible Association Between Zika Virus Infection and Microcephaly — Brazil, 2015. MMWR Morb Mortal Wkly Rep 2016;65:59–62. (historical incidence)
- ibid. (expected incidence – low)
- ibid. (expected incidence – high)
- Latin American Collaborative Study of Congenital Malformations (ECLAMC)
- CDC Facts about Microcephaly (low)
- ibid. (high)
- Virginia Dept of Health fact sheet Microcephaly (low)
- ibid. (high)
- Cleveland Clinic – Microcephaly in Children (low)
- ibid. (high)
- Editors Wanda M. Haschek, Colin G. Rousseaux, Matthew A. Wallig, Haschek and Rousseaux’s Handbook of Toxicologic Pathology, Third Edition, Volume One (Waltham: Elsevier, 2013) 2723. (low)
- ibid. (high)
- BAXTER, P. (2011), Head size: WHOse growth charts?. Developmental Medicine & Child Neurology, 53: 3–4. doi: 10.1111/j.1469-8749.2010.03847.x
- von der Hagen, M., Pivarcsi, M., Liebe, J., von Bernuth, H., Didonato, N., Hennermann, J. B., Bührer, C., Wieczorek, D. and Kaindl, A. M. (2014), Diagnostic approach to microcephaly in childhood: a two-center study and review of the literature. Developmental Medicine & Child Neurology, 56: 732–741. doi: 10.1111/dmcn.12425