Where is Zika most likely to occur in the US?

Zika symptoms
CC BY 2.0 Wikimedia Commons

In the hope of enhancing prevention methods, researchers have predicted potential Zika hot spots in the continental United States.

The Zika epidemic is a vexing one. Spread by Aedes aegypti mosquitoes and sexual transmission, the virus shows no symptoms in 80 percent of those infected – which means those infected may engage in sexual activity without knowing they are at risk of spreading the virus.

And while 80 percent of those infected may not even notice, babies whose mothers contract Zika during pregnancy may develop devastating birth defects and may not survive at all.

With this in mind, researchers at Saint Louis University have set out to predict where Zika would potentially hit hardest in the States; they have put the bulls-eye of Zika transmission on the Mississippi delta, noting that it is likely to be transmitted in southern states extending northward along the Atlantic coast and in southern California.

And while it feels like we’ve had one horror-film virus after the next raising the panic alert to “get me a hazmat suit quick” and “never leaving my house again” levels, the aim of this study wasn’t to terrify, but instead to encourage preparation.

"The purpose of this study was not to create unwarranted alarm, but rather to enhance Zika prevention methods such as mosquito control, effective prevention message dissemination, and treatment and care preparation, in advance of a Zika epidemic in the contiguous U.S.," says Enbal Shacham, Ph.D., M.Ed., from Saint Louis University and the lead author of the study.

"We need significant planning and prevention in areas and populations most likely to experience the highest burdens from Zika infection. Timely strategies to communicate risk, control mosquito populations, and prevent disease transmission are imperative to preventing a large-scale Zika epidemic in the United States," she adds.

The team analyzed 3,108 counties in the U.S. and found 507 "high risk" spots for Zika transmission determined by a number of factors:

The presence of Aedes aegypti mosquitoes; high rates of sexually transmitted infections, which is an established surrogate marker for unprotected sex; number of women of child-bearing age; and an estimate of birth rates for each county.

"Recent reports suggest that the Zika virus can survive within semen for significant amounts of time, and thus, the sexual transmission route of infection may be significantly underestimated," Shacham says. "The sexually transmitted route is also concerning because sexually transmitted infections tend to cluster geographically and occur disproportionately in areas with higher concentrated disadvantage."

One thing that remains unclear is the rate of sexual transmission, so the researchers used three different models of transmission risk: 70, 85, and 100 percent.

Zika map© See larger map at: Saint Louis University

Assuming that Zika is transmitted in 70 percent of the cases of STIs, the researchers estimate between 300,000 to 41.7 million people from high-risk counties could be more likely to contract Zika than individuals who live in other counties in the U.S. Of those at potential higher risk, between 3,700 and 632,000 may be pregnant women, the highest at-risk group.

"Our results also show that complications from the Zika virus are likely to overlap with impoverished counties with large minority populations where resources are more likely to be scarce to combat a large-scale Zika virus outbreak," Shacham says.

According to the press statement, Shacham suggests developing intensive interventions to prevent infection as well as treatment and care plans for families with sick newborns in higher risk areas.

"Enhanced vector control, Zika surveillance, and clinical management in these higher-risk areas will be critical for reducing the impact of a sustained Zika virus outbreak that may potentially occur particularly among economically challenged populations and communities that are least equipped to handle an outbreak."

In the meantime, consider this a friendly reminder. If you live in a high-risk area, devise a good mosquito avoidance plan and keep your sexual activity safe. (Which goes for all areas, really.)

The research was published in the American Journal of Public Health.

Tags: Diseases | Health | Insects

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