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This award-winning blog supplements the articles in Hospital Infection Control & Prevention.

CDC: Zika Expected to Hit U.S. Again as Weather Warms

By Gary Evans, Medical Writer

Any hopes that Zika virus would strike and disappear like SARs and other episodic infectious disease outbreaks have been put to rest by the Centers for Disease Control and Prevention. Zika is fully expected to be a mosquito-borne infection threat in the United States as the warmer months arrive, primarily in the form of a horrific panoply of birth defects to infants born to infected mothers.

"This is the first time a mosquito-borne disease has ever caused birth defects in humans," says Lyle R. Petersen, MD, MPH, director of the CDC’s Division of Vector Borne Infectious Diseases, said at a recent two-day Zika summit at the CDC. “The last time an infectious pathogen – rubella virus – caused an epidemic of congenital defects was more than 50 years ago.”

Infection preventionists know the drill. Though the primary threat is to pregnant women and unborn children, adherence to standard precautions and injection safety should block transmission if patients with Zika are hospitalized or treated in other healthcare settings. But there is an element of unpredictability to Zika that was underscored last year by the surprising ways the virus was transmitted, suggesting the virus has mutated since it first was found in a monkey in a Uganda forest in 1947.

The CDC recently reported Zika-affected pregnancies with birth defects were about 20 times higher than pregnancies occurring before the virus emerged as an epidemic in the the Americas last year.1 “Defects and other early brain malformations, eye defects, and other central nervous system problems, were seen in about 3 of every 1,000 births in 2013-2014,” the CDC reported.

“In 2016, the proportion of infants with these same types of birth defects born to women with Zika virus infection during pregnancy was about 6% or nearly 60 of every 1,000 completed pregnancies with Zika infections. Aggregated data reported to the U.S. Zika Pregnancy Registry lists 47 live births with defects and 5 pregnancy losses.2

The birth defects include microcephaly, with the critical risk period to the fetus occurring in the first trimester of pregnancy, Petersen said. The virus attacks the brain before the cranial plates of the head are fully set, causing them to collapse in to form the small head, he said, pausing to describe the nightmarish anguish of families living with a Zika baby.

“The excessive crying and irritability with this syndrome is really devastating to families because these children basically just incessantly cry 24-hours a day almost,” he said.

That – in stark human terms – is what is at stake as the weather warms, and female Aedes aegypti mosquitoes again dart in and out at all hours and locales, seeking blood meals to produce offspring of their own.

Aedes aegypti has been called the cockroach of mosquitoes,” Judith Monroe, MD, FAAFP, president of the CDC Foundation, said at the Zika summit. “These mosquitoes live indoors and outdoors and lay their eggs in small amounts of water. They bite during the day and night and they bite multiple people during their life spans, creating the potential to spread diseases if the mosquito is infected.”


  1. CDC. Baseline Prevalence of Birth Defects Associated with Congenital Zika Virus Infection — Massachusetts, North Carolina, and Atlanta, Georgia, 2013–2014. MMWR 2017;66(8):219–222.
  2. CDC. Outcomes of Pregnancies with Laboratory Evidence of Possible Zika Virus Infection in the United States. Feb. 21, 2017:

For more on this story see the March 2017 issue of Hospital Infection Control & Prevention.

Gary Evans has written about infectious diseases, occupational health, medical ethics, and a variety of other healthcare issues for more than 25 years. His writing has been honored with five awards for interpretative and analytical reporting by the National Press Club in Washington, DC.