In US, spread of Zika linked to time outdoors

September 14, 2017, Northeastern University
Amount of time spent outdoors. A. Amount of time spent outdoors per day in weekdays in the surveyed Miami-Dade County population and the posterior gamma distribution. B. As A, but for weekends. C. As A, but data are taken from the NHPS survey on the U.S. population. Credit: Ajelli et al (2017)

When Zika first buzzed into the continental United States during the 2016 outbreak, Florida was hit first—and hardest—with 1,174 documented cases to date. So, when Marco Ajelli, associate research scientist at Northeastern and an expert in infectious disease modeling, wanted to study how time spent outside might affect the spread of the epidemic, he chose to focus on the state's most stricken county: Miami-Dade.

What Ajelli found was that the amount of time people spend outdoors impacts their risk for contracting the Zika virus.

Most U.S. Zika infections happen outdoors

Ajelli conducted a survey of 280 Miami-Dade residents and found the vast majority of people spend less than one hour per day outside. The survey also revealed that a small group of people spend a large amount of time outdoors. This is similar to the national average.

"To me that was a surprise, because the kind of weather you can have in Miami compared to Wyoming, for example, is completely different," said Ajelli.

That second group, the findings revealed, were most at risk for Zika infection. That's because, in the U.S. most Zika infections are contracted by people outdoors.

In other regions of the world, such as the tropics, where Zika's impact has been especially severe, mosquito bites mainly occur indoors. Therefore, time spent outside is not a big factor in understanding the epidemic's spread.

But in the U.S., there are certain groups—construction workers, for example—who are much more at risk. According to Ajelli, the vast majority of Zika infections in the U.S. have been contracted by people outdoors. And the first neighborhoods the virus infiltrated in the U.S. were Miami Beach and Wynwood, both known for outdoor public art and beach-related tourist activities.

Few infections, but rapid spread

Using the survey data, plus the latest available knowledge of Zika infection time and transmissibility, Ajelli developed a computational model. It showed Zika would infect few people—predominantly those who spend large amounts of time outdoors—but would spread quickly among that specific population.

Ajelli described his findings in a paper published last week in the journal PLOS Neglected Tropical Diseases. He said the epidemic would spread fast among people who spend lots of time outside because there are fewer of them, they have a high probability of being bitten, and it would take relatively few bites to infect the whole group.

"That means you have less time to put in place a vector control strategy. Whatever strategy you want to implement, you have to be very quick and ready to take action, otherwise it could be too late," Ajelli said.

Ajelli said his findings suggest that outdoor time should be considered an important factor when developing a plan to halt the potential spread of Zika in the U.S. "Maybe just looking at the areas with the highest density of mosquitos is not enough," he explained. "Of course, it is crucial, because you need to target interventions in those areas of the city, but you also have to take into account whether people spend time outdoors."

Explore further: Florida officials: Aggressive efforts to stop Zika continue

More information: Ajelli M, Moise IK, Hutchings TCSG, Brown SC, Kumar N, Johnson NF, et al. (2017) Host outdoor exposure variability affects the transmission and spread of Zika virus: Insights for epidemic control. PLoS Negl Trop Dis 11(9): e0005851. doi.org/10.1371/journal.pntd.0005851

Related Stories

Florida officials: Aggressive efforts to stop Zika continue

March 27, 2017
Florida officials say they're continuing aggressive efforts to stop the spread of the Zika virus.

Costs of Zika fight rise to nearly $30M in Miami-Dade County

May 3, 2017
Miami-Dade County plans to hire a full-time entomologist in its increasingly costly fight against the Zika virus.

Local Zika cases spread to Miami Beach: reports

August 19, 2016
Miami Beach now has cases of Zika infection that appear to have been locally transmitted, US media reported on Thursday, suggesting that the mosquito-borne virus is spreading in Florida.

CDC: Don't donate sperm in three Florida counties due to Zika

March 13, 2017
U.S. health officials say men from three Florida counties shouldn't donate sperm because of the risk of spreading Zika.

Zika testing for all pregnant women who have been in Florida county: CDC

October 20, 2016
(HealthDay)—U.S. health officials are now recommending that all pregnant women who have recently spent time in any part of Miami-Dade County in Florida be tested for Zika infection.

Florida probes four suspected non-travel cases of Zika

July 27, 2016
Florida is investigating two new cases of Zika virus that may not involve people infected while traveling outside the United States, bringing the state's total number of such cases to four, officials said Wednesday.

Recommended for you

Creation of synthetic horsepox virus could lead to more effective smallpox vaccine

January 19, 2018
UAlberta researchers created a new synthetic virus that could lead to the development of a more effective vaccine against smallpox. The discovery demonstrates how techniques based on the use of synthetic DNA can be used to ...

Study ends debate over role of steroids in treating septic shock

January 19, 2018
The results from the largest ever study of septic shock could improve treatment for critically ill patients and save health systems worldwide hundreds of millions of dollars each year.

New approach could help curtail hospitalizations due to influenza infection

January 18, 2018
More than 700,000 Americans were hospitalized due to illnesses associated with the seasonal flu during the 2014-15 flu season, according to federal estimates. A radical new approach to vaccine development at UCLA may help ...

Zika virus damages placenta, which may explain malformed babies

January 18, 2018
Though the Zika virus is widely known for a recent outbreak that caused children to be born with microencephaly, or having a small head, and other malformations, scientists have struggled to explain how the virus affects ...

Certain flu virus mutations may compensate for fitness costs of other mutations

January 18, 2018
Seasonal flu viruses continually undergo mutations that help them evade the human immune system, but some of these mutations can reduce a virus's potency. According to new research published in PLOS Pathogens, certain mutations ...

Study reveals how MRSA infection compromises lymphatic function

January 17, 2018
Infections of the skin or other soft tissues with the hard-to-treat MRSA (methicillin-resistant Staphylococcus aureus) bacteria appear to permanently compromise the lymphatic system, which is crucial to immune system function. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.