By Anthony J. Brown, MD

NEW YORK (Reuters Health) - The aerosolized toxins that come with harmful algal blooms, commonly known as "red tides," significantly impair lung function in patients with asthma, new research shows.

Further studies are needed to determine the long-term effects of exposure to such toxins, but until then, asthmatics are advised to avoid stretches of beach affected by a red tide.

"Red tides can occur all over the world," study co-author Dr. Barbara Kirkpatrick told Reuters Health. In Florida, where her group's study took place, "red tides occur annually in the Gulf of Mexico and are caused by marine microalgae called Karenia brevis."

Findings from animal studies have shown that red tide toxins can cause marked constriction of the airways, noted Kirkpatrick, from the Mote Marine Laboratory in Sarasota. "Our work is really the first epidemiologic study looking at the effects of exposure in people."

The study, which is reported in the medical journal Chest, involved 97 subjects with asthma who were surveyed and underwent tests of lung function before and after spending 1 hour on beaches with or without an active red tide.

The subjects reported significantly more respiratory symptoms following red tide exposure than before exposure, the report indicates. In addition, red tide exposure was associated with significantly reduced lung function. All of these effects were most pronounced in patients who used asthma medications on a regular basis.

Exposure to the beach without a red tide did not significantly affect respiratory symptoms or lung function parameters.

Kirkpatrick said that while adherence to medications is important for prospective beachgoers with asthma, the best measure is simply to avoid beaches with an active red tide. "The good news is that the blooms tend to be really patchy, so it may involve going just a few miles up the road to find an unaffected beach."

To help asthmatics and others avoid red tide beaches in her area, Kirkpatrick's laboratory has outfitted the lifeguards with Blackberry e-mail devices to provide regular reports on beach conditions. This information can then be accessed by the public on the laboratory's Web site (www.mote.org).

SOURCE: Chest, January 2007.