Enterococci in Hawai'I Beach Water

Abstract

Enterococci concentrations are used to develop water quality standards to protect recreational water users from sewage-borne pathogens. In Hawaiʻi, the EnterolertⓇ test (IDEXX Laboratories, Inc.) is commonly used to determine enterococci concentrations in coastal waters, with a threshold of 130 MPN per 100 mL triggering public health advisories by the Hawaiʻi Department of Health (HDOH). This study evaluated the specificity of the EnterolertⓇ test in Hawaiʻi beach water samples and determined the presence of sewage contamination. A total of 49 enterococci-positive beach water samples were collected from 24 different beaches. Of these 49 samples, there were 85 enterococci-positive wells from Quanti-TraysⓇ, of which DNA analysis revealed a false-positive rate of 11.76%, with non-Enterococcus species including Clostridium tertium (2.35%), Vagococcus luciliae (3.53%), Streptococcus gordonii (1.18%), Bacillus (1.18%), Vagococcus bubulae (1.18%), Paenibacillus dendritiformis (1.18%), and Vagococcus fluvialis (1.18%). Microbial source tracking using CrAssphage and the HF183 markers indicated traces of human sewage in 63.3% of enterococci-positive samples (n=49), with CrAssphage detected in 42.9% and HF183 in 36.7%. The source of enterococci in the remaining samples could not be determined. This study suggests that the EnterolertⓇ Test exhibits higher false-positive rates in Hawaiʻi than reported in temperate regions, with a substantial portion of enterococci detections resulting from non-human fecal sources. As a result, this may overestimate health risks in coastal waters and highlights the need for an alternative fecal indicator bacteria better suited to tropical environments.