Current Ebola Guidelines May Put Sewer Workers at Risk

A new study has determined sewer workers could be at risk for Ebola inhalation
Current Ebola Guidelines May Put Sewer Workers at Risk

A recent study from Drexel University and the University of Pittsburgh claims sewer workers may not be adequately protected by guidelines when servicing pipes downstream from Ebola patients.

The study, titled “Risks from Ebolavirus Discharge From Hospitals to Sewer Workers,” outlines a Quantative Microbial Risk Assessment (QMRA) that determines a sewer worker’s risk of contracting Ebola from inhalation exposure while working in a sewer line downstream from a hospital with Ebola patients.

The results of the QMRA suggest there’s a significant enough risk to necessitate further study.

“While an acceptable risk of Ebola virus disease (EVD) illness has not yet been defined, under the least favorable conditions in which PPE is not worn and Ebolavirus RNA copies are deemed as virulent as plaque-forming units, the median potential risk of developing EVD illness from inhalation exposure to Ebola-contaminated aerosols in the sewer is … a value higher than many risk managers may be willing to accept,” the study reads.

This particular Ebola risk to sewer workers isn’t currently addressed by the World Health Organization (WHO) or Centers for Disease Control (CDC). The 2014 Ebola outbreak saw its first cases of the virus treated in the U.S., and WHO’s initial guidelines in August of 2014 stated that wastewater from Ebola patients didn’t require treatment before being disposed of via sewer or pit latrine.

Months later, those standards were upgraded, but they still didn’t adequately protect sewer workers, according to the study’s authors. WHO recommended a set of holding tanks to contain the waste for a week prior to disposal to allow the virus to degrade.

“While current WHO and CDC guidance for disposal of liquid waste from patients undergoing treatment for Ebolavirus disease at hospitals in the U.S. is to manage patient excreta as ordinary wastewater without pretreatment,” the study reads. “Possible worker inhalation exposure to Ebolavirus-contaminated aerosols in the sewer continues to be a concern within the wastewater treatment community.”

The authors went on to recommend precautionary steps like wearing a properly fitted NIOSH-approved N-95 respirator during the handling of untreated sewage. Further studies are looking at the potential benefits of pretreating Ebola-infected wastewater onsite prior to discharge.

There also was some question around some of the assumptions made in the study, and the researchers recommended further investigation into whether patient waste mixes evenly into hospital effluent. “It is more likely that liquid infectious waste would enter the wastewater stream in concentrated ‘pulses’ rather than a continuous stream, resulting in episodically higher exposure doses,” reads the study. “Hospitals that accept Ebola patients in smaller municipalities or other countries may have lower dilution ratios than those in Chicago and Los Angeles, resulting in higher exposure doses in the sewer.”

Researchers also assumed that the hydrophobicities of mesophilic heterotrophic bacteria and Ebola viral particles were the same, which may not be the case. If Ebolavirus was more hydrophobic, the workers’ inhalation risk would be greater.

The team talked to workers at wastewater treatment plants to find out what conditions they could come into contact with untreated sewage aerosols, and then they examined Ebola to build a model of how it might behave under those conditions to build its risk-assessment study.


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