Non-travel zika cases in Fla. could approach 400 by summer’s end

Nearly 400 non travel-related Zika infections will occur in Florida before the end of the summer, according to a new study by biostatisticians at the University of Florida and other institutions.

In addition, the virus is projected to spread to several other Southeastern states with handfuls of cases projected to pop up from Texas to South Carolina and even Oklahoma.

The projections come weeks after the Florida Department of Health identified the nation’s first locally acquired cases of the Zika virus in Miami-Dade County. UF researchers had already produced projections for other countries, which have experienced local Zika virus transmission for months – and in some cases, years.

Though the virus has been in South America for more than a year, some scientists doubted that it would ever come to the United States.

“It wasn’t clear at first whether mosquito densities were high enough to sustain an outbreak in the U.S.,” said Dr. Ira Longini, a professor of biostatistics in the UF College of Public Health and Health Professions and the College of Medicine.

Once the first cases of locally transmitted Zika fever were identified in Miami, however, Longini and his colleagues felt more comfortable publishing 2016 estimates projecting the number of locally transmitted cases that they expect will occur in Florida.

The model projects 395 Zika infections in Florida by Sept. 15 due to local transmission and 79 symptomatic cases by the same date. In addition, they forecast that a median of eight of the infections will be in pregnant women during their first trimester.

Other states expected to see locally acquired Zika are below, followed by the number of locally acquired cases and the number of symptomatic cases:

  • Alabama – 11, 2
  • Arkansas – 3, 1
  • Georgia – 6, 1
  • Louisiana – 4, 1
  • Mississippi – 10, 2
  • Oklahoma – 12, 2
  • South Carolina – 16, 3
  • Texas – 5, 1

Longini, a senior researcher at UF’s Emerging Pathogen Institute, partnered with Dr. Alessandro Vespignani at Northeastern University, Dr. Elizabeth Halloran at the University of Washington, and scientists from several other institutions to produce a website showing how Zika virus has spread through Mexico, the Caribbean, and Central and South America, and projecting how it might spread in the future.

Much of the analysis presented on the website was published last July in bioaRchive.

At UF, Longini worked with Dr. Natalie Dean, a postdoctoral fellow in the department of biostatistics, and Dr. Diana Patricia Rojas, a third-year graduate student in the department of epidemiology, to contribute to the publication.

The three also collaborated with UF biostatisticians Dr. Yang Yang and Dr. Eben Kenah to produce an article in Eurosurveillance on Zika epidemiology and transmissibility in Colombia.

“In Colombia, we’re trying to estimate the proportion of women infected in the first trimester who get microcephaly and other birth defects,” Longini said.

The researchers are partnering with the Colombia National Institute of Health, which has assembled a cohort of 15,000 pregnant women who are either known to have been infected with Zika virus while pregnant or who suspect they were infected.

“That’s the largest cohort in all of Latin America,” Rojas said. “It will give very good information about the exact proportion of pregnant women infected with Zika that can develop birth defects.”

While many researchers have performed retrospective analyses of Zika infection outcomes using data from Brazil and elsewhere in Latin America, none to date have involved prospective cohorts. This cohort will allow investigators to follow pregnant mothers through time, measuring the pregnancy outcomes of those who were likely infected in the in the first trimester of their pregnancy.

The results of this study will help Longini and others further codify the range of birth defects that fall under congenital Zika syndrome, as well as the likelihood of microcephaly and other birth defects.

As many of the prospective mothers began their pregnancies during late 2015 and early 2016, Longini expects to begin learning about their pregnancy outcomes in the fall.

Written by: Evan Barton