The sketchy numbers behind Brazil’s Zika crisis

There are a lot of big numbers flying around as the world struggles to understand and hopefully control the spread of the Zika virus.

The epicenter of this apparent crisis is northeastern Brazil, where there has been a reported surge in children born with abnormally small heads — a condition know as microcephaly.

Media outlets have been quick to jump on a scary connection thought to be between a fast-spreading virus and disfigured babies. But a closer look at the numbers and the terminology being used by government officials and the media suggests everybody should stop to take a very deep breath.

On Friday, the journal Nature published extracts from an eye-opening report by the medical body responsible for monitoring birth defects in Latin America. The report concluded that the apparent spike in babies with small heads “is probably due to active search and over-diagnosis.” This over-diagnosis is being spurred by intense media interest in the story, the report says, and the data so far collected is inconclusive on any connection between Zika and microcephaly.

That’s pretty huge.

But a possible over-diagnosis is not the only problem with the numbers and reporting coming out of Brazil. Let’s take a look at some of the confusing or incorrect information out there, and why it is important to understanding this issue:

• Confirmed cases of microcephaly linked to Zika are still in the single digits: According to the most recent bulletin from Brazil’s Health Ministry, only six of the country’s reported cases of microcephaly are “related to the Zika virus.” Testing for Zika in newborns is a complicated process, and the Brazilian government is working on a simpler, cheaper way to positively identify the virus and distinguish it from other viruses with similar symptoms. 
   
• Most of the suspected cases of microcephaly haven’t been confirmed, and hundreds have been discarded: Several media outlets have reported that 4,000 babies have been born with misshapen, small heads in Brazil. That’s just wrong. There have been about that many suspected cases of microcephaly since October, but that number has fallen. What suspected microcephaly means is that a doctor has measured a baby’s head and found that it is smaller than normal. This is often done while a baby is still inside a woman’s uterus. But many infants with smaller-than-normal heads in gestation end up developing normally, according to medical experts. Cases of reported microcephaly may also turn out to be simply misdiagnosed.So far, of the original thousands of suspected cases, Brazil has confirmed 270 instances of children born with microcephaly since October 2015. And, significantly, 462 cases have been discarded, according to the ministry’s numbers. So cases are being discarded at almost twice the rate that they’re being confirmed.
   
• The number of newborns with small heads in Brazil might not be that unusual: Approximately 8,000 children are born every day in Brazil — one of the largest nations on Earth. Dr. Jim Barkovich, a professor of radiology at the University of California, San Francisco, told GlobalPost that 2 to 3 percent of babies he examines have microcephaly. Many of those “just have small heads,” he said. A small head, in and of itself, isn’t necessarily a sign that a baby will be born with developmental problems, Barkovich said. That's just his anecdotal experience. Other sources peg the national rate in the United States much lower. According to the Centers for Disease Control and Prevention, “microcephaly ranges from 2 babies per 10,000 live births to about 12 babies per 10,000 live births in the United States.” That’s 0.02 percent to 0.12 percent. Even at a rate as low as this one, Brazil could still expect a few dozen cases of microcephaly in any given year.
   
• Historical data may not be accurate: The authorities and media are repeatedly comparing the thousands of suspected microcephaly cases to typical averages of 150 or so per year. That number is about right, as far as known cases go: Brazil’s Health Ministry sent GlobalPost a table showing that reported microcephaly cases from 2010 to 2015 ranged from 139 to 175 annually. But here’s the thing: The Brazilian government in late 2015 put out a bulletin urging pediatricians and clinics to be on the lookout for microcephaly and to be sure to report cases. Since then, the number of reported cases has spiked. It is very possible, as the report Nature highlighted points out, that there has been significant over-diagnosis of microcephaly. It’s also possible, in a country criticized for its record-keeping, that many clinics were not thoroughly reporting microcephaly cases prior to 2015.
   
• Officials have no idea how many cases of Zika there are: When GlobalPost called Brazil’s Health Ministry, they said they had “no idea” how many cases of Zika there were in the country. A spokesman offered a vague range of 500,000 to 1.5 million cases, but he stressed that this number is purely guesswork. “There is no good data,” he said.
   
• There are lots of reasons why children are born with small heads: While the media quickly reported the connection between microcephaly and Zika, the reality is that many different factors can cause babies to develop smaller skulls. UCSF’s Dr. Barkovich cautioned that there could be a host of reasons why it may be happening more in northeastern Brazil, from the Zika virus to congenital factors to malnutrition.
   
• “Microcephaly” is an overly simplistic term: Dr. Thomaz Gollop, who specializes in fetal medicine in Sao Paulo, expressed serious frustration at the incorrect use of the term “microcephaly” by both the media and the Brazilian government. Microcephaly simply means “small head,” and the fetal abnormalities being seen in the northeast are far more complicated, Gollop said. It would be more correct to talk about a Zika “syndrome,” he said — basically a series of symptoms in babies that are probably caused by the Zika virus. The symptoms are much more complex than babies having small craniums, and the simplistic connection between that one symptom and Zika is proving unhelpful, in his view. “Unfortunately, this word has entered the public discourse,” Gollop said. “It’s causing a lot of confusion.”​

Despite all this, there is legitimate concern among experts about the possible link between Zika and birth defects: None of the above discounts the fact that doctors acknowledge something strange is probably going on in northeastern Brazil. Gollop said he has heard serious concerns from his colleagues in the region, and he suspects that many health clinics are probably still not reporting accurate numbers of newborns with birth defects to the Health Ministry. There could be many more cases of children being born with health impacts related to Zika than we know about, he said.

Whatever is going on in Brazil, one thing is clear: There is not enough accurate data yet to show that this is something the global public, or specifically expecting mothers in Latin America, should be panicking about.

This story is crossposted from our colleagues at GlobalPost.