Harmful Algal Blooms in Recreational Freshwater: Expanding Surveillance in Indiana, 2010-2014

BACKGROUND:  

Harmful algal blooms (HABs) are events caused by overgrowth of toxin-producing photosynthetic bacteria in freshwater. Exposure to HABs is associated with adverse health effects in both humans and domestic animals. Few states have historical information on the occurrence of HABs. Indiana started surveillance for HABs in environmental samples in 2010 and expanded surveillance to capture adverse human and animal health effects associated with HABs in 2014. The goal of the state’s program is to improve knowledge of HABs and HAB-associated illnesses within the state and to contribute to national data collection efforts.

METHODS:  

Field samples were collected from May to September for each year in the study period from predetermined swimming beaches owned or managed by the Indiana Department of Natural Resources. Testing for highest cell count and toxin analysis for microcystins, cylindrospermopsin and anatoxin (a) were performed and results were compared with the World Health Organization’s threshold for a “high risk health alert” (≥100,000 cells/mL). Stakeholders received updates weekly on the testing, and appropriate actions (such as posting warning signs and updating the state HAB map) were taken, based on the week’s results. Illness reports were investigated using a standardized form and compared with weekly results to determine the index of suspicion for a HAB event.

RESULTS:  

A median of 10 lakes (range: 5-14) and 63 samples (range: 18-81) were collected each year during the study period. Both the number of lakes sampled and specimens collected increased between 2010-2014. With the exception of 2014, the highest cell count increased each year. In 2012, 76% of all samples had cell counts over 100,000 cells/mL. In 2012 and 2013 16% and 11% of samples had cell counts above 1,000,000 cells/mL, respectively. In 2014, Indiana documented 5 reported HAB events which affected 3 domestic dogs and 2 humans, although only one animal report and one human report were corroborated by investigation.

CONCLUSIONS:   HABs are a complex emerging human and animal health threat for which standardized surveillance does not exist. During the study period, these measurements consistently surpassed established “high risk health alert” thresholds, indicating that the potential for toxin production and potential harm to human and animal health was increased. The implementation of methods to track health effects will help Indiana health officials monitor the state’s lakes, contributing to national data and connecting the public to relevant and timely information for years to follow.