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Delaware Health Alert Network #154

July 29, 2008 8:51 am

Health Advisory

Summer is red tide season. Although there is no known red tide in Delaware, this Health Advisory is sent to inform health care providers about symptoms associated with red tide and to request that they report patients exhibiting symptoms suspected to have been caused by red tide.

Red tides are caused by an increase in algae populations, often called a bloom. The preferred term for these events is algal bloom as there may be colors other than red or no color at all associated with potentially harmful algae population in water. There may also be events that cause a red tint to the water that are not associated with an algal bloom.


Red tides have been known to occur in most of the coastal regions of the world. Delaware experienced a red tide in late August and early September, 2007, due to the presence of Karenia brevis – a naturally-occurring dinoflagellate (single-celled phytoplankton with two flagella). This is the first documented occurrence of the organism north of Cape Hatteras, North Carolina. The organism is primarily found on the Gulf Coast of Florida, and it is believed that an eddy from the Gulf Stream brought K. brevis to Delaware’s near-shore waters. Outbreaks, if they occur, will typically be seen from mid- to late-summer through early fall.

Health Effects

The most well documented health effect from exposure to a HAB is through consuming shellfish that have been contaminated by one of the various species of algae responsible for red tides. Health effects can vary depending on the organism. The organisms that have been found in Delaware can cause neurotoxic shellfish poisoning (NSP). NSP can include gastrointestinal and neurological effects including nausea and diarrhea; dizziness; muscular aches; and tingling and numbness in the tongue, lips, throat, and extremities. Scientists know little about how other types of environmental exposures to brevetoxin—such as breathing the air near red tides or swimming in red tides—may affect humans. Anecdotal evidence suggests that people who swim among brevetoxins or inhale brevetoxins dispersed in the air may experience irritation of the eyes, nose, and throat, as well as coughing, wheezing, and shortness of breath. Additional evidence suggests that people with existing respiratory illness, such as asthma, experience these symptoms more severely. Contact dermatitis is possible if a person swims or bathes in water containing high amounts of the organisms.

Limiting Exposure

The best protection is to avoid contact with contaminated waters and nearby areas, as well as the ingestion of fish and shellfish from such waters. Information about current conditions in Delaware can be obtained from the Department of Natural Resources and Environmental Control at: or by calling 1-800-922-WAVE.

To Report Suspect Cases


  • Division of Public Health, Bureau of Epidemiology: 1-888-295-5156; or
  • Department of Natural Resources and  Environmental Control: 302-739-9939

For Further Information

Categories of Health Alert messages:

  • Health Alert: Conveys the highest level of importance; warrants immediate action or attention.
  • Health Advisory: Provides important information for a specific incident or situation; may not require immediate action.
  • Health Update: Provides updated information regarding an incident or situation; unlikely to require immediate action.
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