Zika Virus

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What is the Zika virus? Should you be worried about it? And is it really causing severe birth defects in Brazil?

For more information about Zika:

CDC: http://www.cdc.gov/zika/

European Center for Disease Prevention and Control: http://ecdc.europa.eu/en/publications/Publications/zika-virus-americas-association-with-microcephaly-rapid-risk-assessment.pdf

Suprisingly on point opinion piece in the Daily Beast: http://www.thedailybeast.com/articles/2015/12/24/doctors-warn-brazilian-women-don-t-get-pregnant.html

To answer the question about the specifics as to why I am so skeptical of Brazil’s reportedly extremely low baseline rate of microcephaly, here’s my response that I copied and pasted from the comments below:

Essentially, there are 2 reasons why Brazil’s baseline rate of microcephaly is implausible.

1. In the medical literature, there are 2 definitions of microcephaly used/advocated for: A head circumference that is either 2 or 3 standard deviations below the mean. For any body measurement that adheres to a normal distribution in the population, we would expect .0014% of the population to fall below 3 SDs of the mean – this is an inviolatable rule of statistics (https://en.wikipedia.org/wiki/68-95-99.7_rule). If head circumference adheres to a normal distribution, then one can calculate that, on average, we would expect ~4200 babies per year in Brazil to have microcephaly (0014% x ~3 million births in Brazil per year). It’s very true that head circumference likely does not strictly adhere to a normal distribution, since profoundly small head circumference (while rare) is still more common than profoundly large head circumference . However, it’s hard to imagine that the distribution of head circumference would be so dramatically skewed such that 4200 microcephalic babies per year becomes just 150.

2. In the medical literature, there is a surprising lack of good data on the empirically measured rates of microcephaly in the population, which could be used to determine if it is normally distributed. In the few primary papers that exist, some of which date to the 1950s, the reported incidence vary 100 fold between different countries. While the rates of individual diseases can vary 100+ fold between countries, microcephaly isn’t an individual disease, but rather a syndrome and/or sign of dozens if not hundreds of different conditions – which are a mix of prenatal infections, maternal drug/toxin exposure, and genetic/chromosomal diseases. It is implausible that a condition with such a huge variety of causes, some of which will be more likely in country A while others will be more likely in country B, would have such a difference in incidence in different parts of the world. In other words, the regional/geographic effects of the incidence of individual causes of microcephaly get averaged out when all causes are considered collectively. So there cannot be a 100 fold variation in the true incidence of microcephaly between countries. With the limited country-specific data that exists, Brazil sits at the extreme low end of incidence.

You could ask, why would I less believe Brazil’s reported baseline microcephaly incidence of 0.005%, than a country like the US with a much higher reported incidence? It’s because it’s much more likely that cases of microcephaly get underreported than overreported, particularly if a newborn technically meets the definition based on head circumference, but has no other obvious physical or developmental problems. If I’m a pediatrician, I may not want to label the patient microcephalic, since that may unnecessarily upset the parents, who will then believe there is something wrong with their child, when there very well may not be – some otherwise normal kids just have small heads.

In addition, as with mandatory reporting of certain infectious diseases in the US, not every doctor takes the time to do the official reporting, or even knows how the reporting process works. So the official count of any disease is lower than reality.

Therefore, irrespective of which specific countries have a low reported rate of microcephaly and which have a high reported rate, the high reported rate is more likely to be accurate. And as mentioned above, Brazil has an unusually low reported rate compared to other countries – thus the reason I don’t believe it.


MSPA 2017 says:

Great! Thank you for uploading.

José Ricardo L.Pinto says:

Great video! Keep on the great job in medical education! thank you

Buzzard King51 says:

Oh no chicken little! The Zika virus is gonna get you! It's more deadly than the bullshit hoax known as Charles Manson. Hide under your bed. The Zika virus is coming! Ooooh.

Marcelo Ave says:

I was under the impression that the American CDC had sent a task force to evaluate all data concerning this supposed relationship between the zika virus and microcephaly in northeastern Brazil. the media's grasp is strong over both patients and doctors alike. As you have so eloquently pointed out, statistical discrepancies and sound critical thinking are not very popular.

shif442 says:

why you removed the recent copd video?

Dominique Pordeus says:

Thank you! I was an intern at a big infectious disease hospital in northeastern Brazil and I saw the outbreak of a new disease very similar to Dengue, we thought it was Chikungunya fever, now we know it was Zika. Than, this year we saw the increase of microcephaly cases when I was an intern at an obstetrics/pediatrics service of my state, so this was very real to me. The relationship between the virus and the increase of microcephaly is not very clear yet, but the media talks about it like it is an absolute truth. Many pregnant women are scared, even though the absolute risk of having a baby with microcephaly after the mother had Zika is very low. We advise them to do what you just said, wearing long sleeves, using repellents, and specially to look at their own houses and neighborhood for places where the Aedes Aegypti mosquito could reproduce, so we can decrease the number of this vector as much as we can. It is very difficult, we have seen Dengue outbreaks for years…

PhilaPeter says:

I always catch myself saying something is "exciting" or "interesting" only to realize it's totally morbid for normal people. As always, thanks for the upload.

MT LGP says:

Hello Dr. Eric!The video was very informative, and yes, media reports tend to confirm the relation of Zika and this supose rise of microcephaly cases as a scientific fact, especially here in Brazil, but I did not understand why the numbers of microcephaly does not make sense as you say at 7:33, may you explain it for me?

justbizun says:

Excellent video! Thank you for adding the much needed skepticism to this topic

Robson Vieira says:

Dr Strong, I'm a physician in the Brazil's northeast region. I'm working with Adult Intensive Care and never have oportunity to see a microcephaly newborn. What concerns us here is the regional concentration of the cases (mostly on states of Pernambuco and Bahia) in a short time fashion. I got zika too and got the full set of symptons (including conjuntivitis and arthralgias with swelling in the joints witch lasts one week and has a crânio-caudal pattern of temporal onset). I was worried about me because little is know about the full clinical spectrum of symptons and natural hystories of infected patients. But I survived! (#LOL) Thanks for the hard working on these videos. I'm a proud and old fan of you.

shastagulch says:

Another great video, Dr. Strong. Thank you!

MK REDDY says:

Highly though-provoking. Thank you, Sir. Appreciate the efforts taken. Cheers.

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