High concentrations of harmful bacteria lurk in the Hilo watershed, according to a study by University of Hawaii researchers
A paper published in the Journal of Environmental Quality found that bacteria such as Staphylococcus aureus — a bacterium that can cause a wide range of illnesses ranging from mild to life-threatening — are found in large concentrations in the soil around Hilo Bay, and enter the bay through storm runoff.
The paper is a follow-up to a 2019 study by the same researchers, which identified that concentrations of Staphylococcus and similar bacteria increase in the bay following immediately following rainfall. That study noted that Hawaii has some of the highest rates of community-acquired staph infections in the nation.
Tracy Wiegner, UH-Hilo professor of marine science and one of the researchers on both studies, said the high staph concentrations in the soil is likely caused by human presence.
By taking soil samples at locations throughout Hilo between 2017 and 2018, Wiegner and her fellow researchers determined that the concentrations of harmful bacteria were greatest in urban soils, with “hot spots” around river mouths and high-density urban areas.
The paper concludes that the most likely source for the bacteria colonies is humans, human-domesticated animals or pests like rats.
“One in four people are natural carriers of MRSA (a staph strain resistant to some penicillin derivatives),” Wiegner said. “That’s why at public pools they ask you to take a shower before you get into the pool, so your bacteria doesn’t get in the water with everyone else.”
Wiegner said a staph carrier can spread the bacteria to their surroundings through the natural shedding of skin cells. In certain conditions — particularly, the warm and moist conditions of a tropical isle — the bacteria can continue to survive in the soil, and can eventually be washed by rainfall into waterways and, eventually, the sea.
That the water conditions in Hilo Bay can be harmful for human health will be unsurprising to few, Wiegner said — she said that, anecdotally, surfers and other people who spend time around the water report the highest frequency of staph infections. But, she added, the knowledge of where and how the bacteria is entering the water could allow health authorities to take steps to mitigate its spread.
While Wiegner said there is probably no simple way to disinfect an area of harmful bacteria without significantly harming the rest of the life in the area, she said communities around the Great Lakes on the mainland have used infrastructure such as maintaining streamside wetlands to retain stormwater, or conducting regular beach grooming to improve water safety.
Until then, she said, residents should be wary of contacting water after a storm: “If the water’s brown, you shouldn’t go near it.”
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.