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Skyrocketing cases of Zika in Puerto Rico


puerto-rican-flagThe headlines are shocking. The New York Times states “Zika Cases in Puerto Rico Are Skyrocketing.” Most other media outlets follow with similar ledes. Is it true? Or, is it just more lies, damn lies and statistics?

Don’t blame the Times. The hysteria about Zika viral illnesses is being stoked by the top public health authorities in the United States. The Centers for Disease Control and Prevention are pushing the meme that Puerto Rico will see a quarter of the island’s population exposed to the disease.

At the root of the latest media hysterics is the latest report from Puerto Rico about the number of pregnant women testing positive for Zika viral illnesses.

Adams L, Bello-Pagan M, Lozier M, et al. Update: Ongoing Zika Virus Transmission — Puerto Rico, November 1, 2015–July 7, 2016. MMWR Morb Mortal Wkly Rep. ePub: 29 July 2016. DOI:

Let’s look at the data:

Pregnant Women Tested for Zika 11/1/15-7/7/16
Symptomatic 2,035 21.8% 383 18.8% 58 2.9%
Asymptomatic 7,308 78.2% 43 0.6% 188 2.6%
TOTAL 9,343 426 4.6% 246 2.6%

In the last eight months, Nov. 1, 2015 through July 7,2016, 7.2% of the pregnant women laboratory tested for a Zika viral illness have had it confirmed or presumed. In that same time frame, a total of 5,582 patients, including these 672 pregnant women, have tested positive. Pregnant women represent 12% of all the patients confirmed to have Zika viral illnesses.

The number of blood donations found to be infected with Zika is also illustrative. From Apr. 3, 2016 through July 3, three months, a total of 18,163 donation specimens were tested and 143, 0.8%, were found positive for Zika. Those donations were discarded.

The CDC says:

the most recent data indicating that 5% of asymptomatic pregnant women … have evidence of recent infection in the most recent reported week of screening (week beginning July 3)

Putting that into perspective, “5% of asymptomatic pregnant women” works out to be 11 women.


  1. 92.8% of pregnant women tested for Zika did not have the illness.
  2. 99.2% of all blood donations, and thus the people donating, tested for Zika did not have the illness.
  3. In the last eight months, 672 pregnant women are known to have contracted a Zika viral illness.
  4. The CDC reports one “poor outcome among pregnancies with laboratory evidence of possible Zika virus infection reported to the Zika Active Pregnancy Surveillance System” for Puerto Rico.
  5. In the tested pregnant women, 34.4% of positive cases were asymptomatic.
  6. Asymptomatic cases of Zika appear far less common than believed.

Are cases skyrocketing? That depends on how you define the word. Will thousands of Puerto Rican children be affected by their mother’s having contracted a Zika viral illness? Perhaps, but the current data suggests that it will be years before an accumulated total that high is reached.

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