Sewer workers could be at Ebola risk with current guidelines

Turns out, the guidelines from the U.S. Centres for Disease Control and Prevention and the World Health Organization might not go far enough to protect sewer workers from Ebola virus.

Research from Drexel University and the University of Pittsburgh suggests that the sewer workers downstream of hospitals and treatment centres could contract Ebola via inhalation.

The study takes the first steps toward understanding the risk that this untreated waste poses to the people in the water treatment process who work in close proximity to it.

"During the 2014-16 Ebola outbreaks we had our first case of Ebola treated in the U.S. and by the end 11 individuals had been treated here, so this is certainly an area of risk assessment that we need to examine more closely," author Charles Haas said.

Initial guidelines issued by the WHO during the outbreak suggested that liquid waste generated by individuals being treated for Ebola could be disposed of via sanitary sewer or pit latrine without additional treatment. Months later it issued more conservative guidelines that suggested containing the waste in a holding tank before releasing it into the water treatment system. But according to the researchers, neither of these advisories accounted for risk to the sewer workers.

"While current WHO and CDC guidance for disposal of liquid waste from patients undergoing treatment for Ebola virus disease at hospitals in the U.S. is to manage patient excreta as ordinary wastewater without pre-treatment. The potential for Ebola virus transmission via liquid waste discharged into the wastewater environment is currently unknown," the authors wrote. "Possible worker inhalation exposure to Ebola virus-contaminated aerosols in the sewer continues to be a concern within the wastewater treatment community."

The team arrived at its conclusions by first talking to workers at urban wastewater treatment facilities to understand where and under what conditions they might come in contact with untreated sewage aerosols. The researchers then looked at previous Ebola data to create a model of its behaviour under similar conditions from which they conducted a standardized microbial risk assessment analysis that was developed by Haas.

It took into account variables such as the amount of waste produced during a treatment period, the degree to which it is diluted, the length of time between its disposal at the hospital and when sewer workers would encounter it and the concentration of viable viruses that could be in the air at treatment facilities.

A worker's risk of exposure varies with the time spent in the contaminated area and whether or not they're wearing properly fitting protective gear, so the team looked at what the exposure risk would be given a range of protection and viral particle concentration scenarios.

"Under the least-favorable scenario, the potential risk of developing Ebola virus disease from inhalation exposure is a value higher than many risk managers may be willing to accept," they reported.

The team added, "Although further data gathering efforts are necessary to improve the prevision of the risk projections, the results suggest that the potential risk that sewer workers face when operating in a wastewater collection system downstream from a hospital receiving Ebola patients warrants further attention and current authoritative guidance for Ebolavirus liquid waste disposal may be insufficiently protective of sewer worker safety."

While this study suggests that new guidelines from the leading public health authorities are likely in order, the researchers acknowledge that their work is part of the iterative process of understanding how to safely contain and treat the virus.

The study is published in the journal Water Environment Research.