The Lincoln Memorial Reflecting Pool in Washington, D.C. isn’t alone in grappling with an algae issue. A recent report from the Centers for Disease Control and Prevention has highlighted that toxins from marine algae and other sea life are frequently making Americans ill. CDC scientists analyzed outbreak data from the past decade and discovered that hundreds of outbreaks related to marine toxins have occurred since 2011, often linked to fish or shellfish contaminated with these toxins. Alarmingly, researchers suggest that the frequency and intensity of harmful algal blooms may increase the risk of these outbreaks in the future. “Geographic spread, greater frequency, and severity of harmful algal blooms in U.S. coastal waters could elevate the presence of ciguatoxin and shellfish-associated toxins in aquatic animals,” they stated in their paper published last week in the CDC’s Morbidity and Mortality Weekly Report.
Marine toxins lead the way among noninfectious foodborne outbreaks. Interestingly, according to the CDC authors, this marks the first comprehensive summary of the impact of these outbreaks on a national scale. There are generally two types of marine toxins. Certain algae produce neurotoxins, with ciguatoxins being the most common linked to human health issues. Small fish consume the algae, which are then eaten by larger fish, effectively moving up the food chain. While ciguatoxins don’t harm the fish that produce them, they can build up in larger predators like bass or snapper, potentially making those who consume them quite sick, or in severe cases, leading to death. Additionally, shellfish that filter algae can also absorb toxic levels during algal blooms.
The other prevalent type of marine toxin-related illness is known as scombroid fish poisoning, named for the fish that primarily cause it—like tuna and mackerel, although others can be involved too. This occurs when these fish are stored improperly, specifically at temperatures above 40 degrees Fahrenheit (4.4 degrees Celsius), allowing bacteria to convert a compound called histidine into histamine and other toxins. Consuming these histamine-infused fish can trigger allergic reactions. Between 2011 and 2023, the CDC identified 402 foodborne outbreaks tied to marine toxins, resulting in over 1,280 illnesses, 96 hospitalizations, and one death. About 95% of these outbreaks involved either scombroid toxins or ciguatoxins, with shellfish toxin outbreaks being less frequent but often more serious; at least 25% of illnesses from these outbreaks required hospitalization.
The researchers believe these figures likely underestimate the real situation. There are no easy diagnostic tests available for human marine toxin poisoning, and both patients and doctors might overlook these toxins as a potential cause of illness—many doctors may also be unaware that these cases should be reported to local health authorities.
So, what can be done? Unfortunately, marine toxins resist typical food safety measures, such as cooking. They are also tasteless and odorless, although fish affected by scombroid toxins might exhibit a “honey-combed” texture or a metallic taste. While many cases are mild or short-lived, some individuals may suffer from severe, long-lasting symptoms that can persist for months or even years. However, the authors suggest that there are strategies to reduce the risk of these outbreaks.
“Preventing scombroid toxin poisoning hinges on maintaining proper temperature control of seafood. A thorough understanding of food safety practices, especially regarding imported fish and restaurant handling, is vital for prevention,” they noted. They also pointed out that most outbreaks linked to ciguatoxin and shellfish-associated toxins are connected to seafood harvested recreationally, emphasizing that targeted communication about affected areas and species is crucial for preventing outbreaks related to algal toxins in recreational fishing contexts.
