An article published today (Feb. 19, 2016) by Mike Stobbe of the Associated Press emphasizes that the link between the Zika virus and the increases in cases of microcephaly in Brazil is, thus far, based only on circumstantial evidence.
The article disputing the widely perceived claim that causation between Zika and microcephaly has been proven is being picked up by major newspapers, including The New York Times,1 The Washington Post,2 and The Seattle Times,3 as well as other major news sources such as ABC News4 and Fox News.5
The Stobbe article references a blanket confirmation last week by Brazil’s Minister of Public Health Marcelo Castro that he was “absolutely sure” of the causal relationship between Zika and microcephaly. Stobbe quotes University of Michigan epidemiologist Dr. Arnold Monto, who disagrees, and points out that, “The simple presence of the virus doesn’t mean it caused the birth defect.”1 2 3 4 5
In other words, correlation is not causation.
This correlation is not causation discrepancy was highlighted in an opinion piece published by The Vaccine Reaction yesterday (Feb. 18, 2016) titled “Brazil at Odds With WHO and CDC on Zika-Microcephaly Link.”6
In his article, Stobbe also quotes University of Pittsburgh microbiologist Dr. Ernesto Marques, who noted that that proving a causal relationship between Zika and microcephaly is akin to prosecuting a murder investigation, with Zika as the supposed killer but with many unanswered questions. Stobbe quoted Dr. Marques as saying,
What you have so far, the victim is there, and you find a person right there that has a smoking gun in his hand. But you still need to close the deal.1 2 3 4 5
The Stobbe AP article stresses the need for conducting a series of studies that would provide stronger scientific evidence of a causal link and cites one study by the U.S. Centers for Disease Control and Prevention (CDC) that is scheduled to begin next week. That study will involve 100 babies in Brazil with microcephaly and about 100 babies without microcephaly. Another study by the Brazilian government will begin in April. That one will involve 200 babies with microcephaly and 400 without the birth defect.1 2 3 4 5
Stobbe quotes Dr. Marcos Espinal of the Pan American Health Organization (PAHO) as saying that the study by the Brazilian government will be the ‘first one to tell us if there’s strong evidence.”1 2 3 4 5
But even then, the evidence would not be conclusive without prospective studies being conducted. Stobbe paraphrased Dr. Espinal…
While these studies can sort out potential causes, experts say they need to be confirmed with research that follows people forward. Colombia, for example, will be following 2,000 Zika-infected pregnant women to see what happens with them and their pregnancies.1 2345
According to Stobbe, “It will take a combination of studies and laboratory evidence to finally determine if Zika is the villain it appears to be, experts say.”1 2 3 4 5
1 Stobbe M. Can scientists prove Zika virus is causing birth defects? The New York Times (Associated Press release) Feb. 19, 2016.
2 Stobbe M. Can scientists prove Zika virus is causing birth defects? The Washington Post (Associated Press release) Feb. 19, 2016.
3 Stobbe M. Can scientists prove Zika virus is causing birth defects? The Seattle Times (Associated Press release) Feb. 19, 2016.
4 Stobbe M. Can scientists prove Zika virus is causing birth defects? ABC News (Associated Press release) Feb. 19, 2016.
5 Stobbe M. Can scientists prove Zika virus is causing birth defects? Fox News (Associated Press release) Feb. 19, 2016.
6 Cáceres M. Brazil at Odds With WHO and CDC on Zika-Microcephaly Link. The Vaccine Reaction Feb. 18, 2016.
Luis Correia, who teaches scientific method at the Bahia School of Medicine and Public Health, said the small-scale studies cited by health officials don’t equal proof. “There appears to be a sort of scientific illiteracy within the ministry that has led them to mix up association with causality,” said Correia. “They are confusing hypothesis with fact.”
Here is a relevant article in the June 2016 issue of Significance – a joint publication of the Royal Statistical Society and the American Statistical Association.
-Earlier this year, World Health Organization experts said that “a causal relationship between Zika infection during pregnancy and microcephaly is strongly suspected, though not yet scientifically proven”. How might scientists prove such a link?-
Here is the link to the article:
Zika virus and birth defects: correlation or causation? http://onlinelibrary.wiley.com/doi/10.1111/j.1740-9713.2016.00913.x/abstract
Rossi A. Hassad, PhD, MPH
Professor, Mercy College, New York
Epidemiologist & Medical Statistician
Member of the American College of Epidemiology
Chartered Statistician and Fellow, the Royal Statistical Society, UK