By Megan Sam
New research delivers the clearest evidence so far that exposure to Florida’s red tide drives measurable increases in acute respiratory and gastrointestinal illness. By pairing bloom data with healthcare records, scientists documented a direct rise in short-term symptoms — offering a rare, detailed look at red tide’s immediate health impacts. This study was carried out by a cross-disciplinary University of Florida (UF) team from medicine, public health and environmental science, led by Chengrong Wang, Ph.D., a data scientist in the UF College of Medicine.
“This study is among the first large-scale, causal analyses to link Florida’s red tide blooms with clinically validated health outcomes,” David Kaplan, Ph.D., associate director of the University of Florida’s Center for Coastal Solutions (UF CCS) and co-author of the study, said.
As part of the CCS co-led Florida Digital Twin project, the research team analyzed medical records from more than 137,930 individuals exposed to red tide between 2012 and 2019, using data from the OneFlorida+ Clinical Research Network, the largest in the southern United States. They matched these records with red tide measurements from the Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute’s long-term monitoring program, allowing them to directly compare health outcomes with bloom conditions.
Decades of investment by the state in environmental and health data systems made this type of research possible, Kaplan noted, and gave the team access to extensive, high-quality datasets needed to explore red tide’s impact on human health.
Red tides occur when blooms of Karenia brevis release toxins that can kill fish, birds and marine mammals. These toxins can harm people as well, contributing to asthma flare-ups, coughing, headaches and increased ER visits for breathing problems, with some evidence pointing to possible gastrointestinal and neurological effects. However, past research on human health effects mostly focused on correlation, not causation. Previous studies were also often small, relied on self-reported symptoms, or did not fully account for how airborne toxins can drift inland, affecting people far from the shoreline.
“Red tide dynamics are still not well understood, and measuring their impact on people’s health, which is influenced by many factors, requires creative solutions with multidisciplinary teams,” Nick Chin, Ph.D., a postdoctoral researcher at the UF Water Institute and co-author, said.
To strengthen and expand upon previous findings, the researchers applied causal modeling to the datasets to determine whether red tide blooms were directly contributing to respiratory, gastrointestinal and neurological symptoms. They found a modest yet consistent rise in the risk of respiratory and gastrointestinal illnesses, with onshore winds potentially carrying toxins farther inland and raising that risk. No similar pattern emerged for neurological symptoms, where the evidence remained unclear.
These insights also allow scientists to estimate how illness rates might climb as blooms worsen. For example, in a coastal city of 400,000 residents, a severe red tide event could be associated with roughly 1,320 breathing-related illnesses and 480 extra stomach-related illnesses every month, putting added strain on local healthcare systems.
“It took oceanographers, hydrologists, data scientists and physicians all speaking the same language to connect water quality and health. The blending of ecological monitoring with electronic health records was complex, yet really powerful,” Kaplan said. “Now, we’re able to quantify how harmful algal blooms translate into measurable increases in respiratory and gastrointestinal illness across the region.”