NEW YORK (Reuters Health) – Several cases of respiratory illness that occurred last year in northeastern Florida were brought on by exposure to a so-called red tide caused by the toxic marine organism, Karenia brevis, health officials conclude in a report released Thursday.

This harmful algal bloom organism is known to produce neurotoxins called “brevetoxins,” which are responsible for neurotoxic shellfish poisonings and respiratory illness.

According to the report, the detection of this red tide event “was unusual because public health authorities were first alerted by a cluster of reported symptoms of human respiratory illness among dredging workers rather than by more common means (e.g., observation of dead fish or birds, detection of contaminated seafood, or use of satellite imagery or routine beach water sampling.”

The illnesses, which involved 20 workers at a beach restoration worksite in Fernandina Beach, were reported to the Nassau County Health Department on September 25, 2007. The most common symptoms were coughing and throat irritation followed by eye irritation, sneezing, and sniffling.

Many of the workers said that their symptoms came and went as they went to and from work each day. None of the workers required medical care and all of them were able to perform their jobs without impairment. After these cases surfaced, public health agencies began receiving reports of similar illness up to 200 miles south of Fernandina Beach.

Testing of water samples near the worksite and at other locations with similar cases revealed the presence of K. brevis. Initial samples showed medium levels of the organism, but testing in Jacksonville, which is 35 miles south of Fernandina Beach, showed high levels. However, after a major storm hit on September 29, levels began to decline. By November 8, all test samples were clear of the organism.

“During this red tide event, prompt investigation of a small cluster of symptoms led to quick identification of the K. brevis bloom. This public health vigilance enabled authorities to take immediate action to issue advisories and otherwise alert the public to an illness of environmental etiology,” the report concludes.

SOURCE: Morbidity and Mortality Weekly Report, July 4, 2008.