Rainfall and Streamflow Effects on Estuarine Staphylococcus aureus and Fecal Indicator Bacteria Concentrations

Abstract

Pathogenic bacteria in nearshore waters are a public health threat, and many have watershed sources. Hence, understanding direct and indirect causes of bacterial loading can improve awareness and watershed management. Rainfall-driven runoff influences river discharge, affecting pathogen transport to the ocean. This study assessed pathogen loading to nearshore waters under varying weather conditions within Hilo Bay, Hawaii, from 2014 to 2017. Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), and fecal indicator bacteria (FIB) were quantified in the bay, rivers, and potential watershed sources using culturebased methods. Relationships between their concentrations with rainfall, river discharge, and water quality data were examined. Staphylococcus aureus, MRSA, and FIB were present within Hilo Bay and its rivers, as well as road runoff, sewage, and soils; MRSA was less prevalent. Staphylococcus aureus and FIB concentrations increased with rainfall and river discharge. Turbidity and salinity were the best water quality parameters for predicting bacteria concentrations, with positive and negative relationships, respectively. Our results suggest that more intense storms, especially after longer dry periods between events, will increase S. aureus and FIB loads to nearshore waters, as storms comprise >80% of annual river loads. Our models can be used to assess recreational water users' health risks and predict future water quality conditions with changing rainfall patterns.

Review Article: Hawai‘i's Cesspool Problem: Review and Recommendations for Water Resources and Human Health

“…Recreational water quality is important to residents and visitors who use Hawai‘i's ocean resources (Kirs 2018). However, little is known about baseline bacteria levels and transport dynamics of bacteria and viruses in wet tropical and subtropical regions where recreational water use occurs year‐round (Strauch et al 2014; Rochelle‐Newall et al 2015; Strauch 2017; Economy et al 2019). Pathogens such as Staphylococcus aureus are recognized as a potential environmental human health threat, though S. aureus is naturally found in the environment and on the skin and nasal passages of most healthy humans (Zetola et al 2005; and see Economy et al 2019).…”

“…However, little is known about baseline bacteria levels and transport dynamics of bacteria and viruses in wet tropical and subtropical regions where recreational water use occurs year‐round (Strauch et al 2014; Rochelle‐Newall et al 2015; Strauch 2017; Economy et al 2019). Pathogens such as Staphylococcus aureus are recognized as a potential environmental human health threat, though S. aureus is naturally found in the environment and on the skin and nasal passages of most healthy humans (Zetola et al 2005; and see Economy et al 2019). Nonetheless, recreational bathers in Hawai‘i are four times more likely to develop S. aureus infections (Charoenca and Fujioka 1995; Economy et al 2019; Taylor and Unakal 2019) and these infections on the skin can cause boils, impetigo, styes, folliculitis, and furnacles (Minnesota Department of Health 2010).…”

“…Pathogens such as Staphylococcus aureus are recognized as a potential environmental human health threat, though S. aureus is naturally found in the environment and on the skin and nasal passages of most healthy humans (Zetola et al 2005; and see Economy et al 2019). Nonetheless, recreational bathers in Hawai‘i are four times more likely to develop S. aureus infections (Charoenca and Fujioka 1995; Economy et al 2019; Taylor and Unakal 2019) and these infections on the skin can cause boils, impetigo, styes, folliculitis, and furnacles (Minnesota Department of Health 2010). Economy et al (2019) identified S. aureus and Methicillin‐resistant S. aureus (MRSA) in wastewater effluent in Hawai‘i and showed relationships with other FIB in nearshore waters of Hilo, Hawai‘i.…”

“…Nonetheless, recreational bathers in Hawai‘i are four times more likely to develop S. aureus infections (Charoenca and Fujioka 1995; Economy et al 2019; Taylor and Unakal 2019) and these infections on the skin can cause boils, impetigo, styes, folliculitis, and furnacles (Minnesota Department of Health 2010). Economy et al (2019) identified S. aureus and Methicillin‐resistant S. aureus (MRSA) in wastewater effluent in Hawai‘i and showed relationships with other FIB in nearshore waters of Hilo, Hawai‘i.…”

“…The authors believe improved identification of specific bacterial sources posing threats to human health will assist appropriate government institutions or local organizations in creating localized watershed management strategies as preventative measures, with the aim of reducing pathogen loads from multiple sources (stormwater, OSDS, agriculture). Models developed for wet tropical regions, such as that by Economy et al (2019), use hydrologic and water quality metrics to predict pathogen loading to nearshore waters. Such models could inform water resource managers regarding health risks to recreational water users in Hawai‘i and other insular tropical and subtropical environments.…”