Local water quality managers say it's unlikely that potentially lethal bacteria flushed into sewer systems from hospitals could survive the wastewater treatment process and get into the ocean to sicken swimmers and beach-goers. But they acknowledge they do not know for sure.
Their statements come a day after a Los Angeles Times article raised questions about the potential for a group of deadly antibiotic-resistant bacteria known as CRE — Carbapenem-Resistant Escherichia coli — to get into the sewer system, multiply and thrive at local wastewater treatment plants before being discharged into the ocean.
CRE is difficult to treat, and it kills half of those who become infected, according to the Centers for Disease Control. The rise of antibiotic-resistant bacteria has been so swift and threatening to the nation's public health that a group of science advisors to President Barack Obama said confronting the risk should be a national priority.
Recent concerns have arisen from a study published last fall by the U.S. Environmental Protection Agency that found CRE in all samples of partially-treated water at seven wastewater treatment plants around the country. The EPA declined to identify which plants were tested. The agency also did not provide the rationale for why the locations were withheld.
At the same time, a group of researchers published a study saying CRE posed a serious threat of becoming established at hospitals and medical facilities unless coordinated efforts were taken to stem their spread. The study used Orange County as a model.
But regional wastewater managers say it's unlikely any CRE coming from hospitals through sewage would pose a public health problem.
"The probability of having drug resistant bacteria come in through (the municipal waste stream) is very low, in the sense that the flow that comes in from hospitals is a small fraction of the flow that we get," said Tim Dafeta, manager of the Hyperion wastewater treatment plant operated by the Los Angeles Department of Sanitation.
Health care facilities account for one-half of one percent of the municipal waste stream, Dafeta said. Any CRE or other antibiotic-resistant bacteria would be a much smaller fraction of the sewage coming from hospitals. The sewage goes through several treatment steps, including being held for 13 days at 128 degrees.
Still, Dafeta and a colleague who monitors Los Angeles water treatment plants said they don't know for sure if that process kills CRE.
“We haven’t really studied that, said Mas Dajori, manager of environmental monitoring for L.A. Sanitation. “We don’t know about the drug-resistant bacteria, but certainly salmonella, and a number of other enteric viruses, and eggs of parasites, so we know that that capture does kill those infectious agents,”
The sanitation department does not test for CRE in incoming wastewater or the treated water sent by an outfall pipe five miles out to sea. But Dafeta said any CRE that made it through the waste treatment process would be so diluted that it would be only a tiny amount of what gets put into the ocean. What flows to the Pacific from the Hyperion plant comes out 190 feet underwater. Dafeta said it's too cold there for any surviving bacteria to multiply.
The city has three other water treatment plants that send wastewater to the ocean. One on Terminal Island discharges highly treated water into Los Angeles Harbor, and two inland plants in Glendale and Van Nuys release water into the L.A. River that's been through the wastewater treatment process and additionally treated with chlorine.
A study published in September by Rice University professor Pedro Alvarez said antibiotic resistant genes (of which CRE is a subset) have been shown to survive wastewater treatment including chlorination at two plants in Northern China.
The EPA did not collect samples for its study from Los Angeles' four city wastewater treatment plants, said L.A. Sanitation's Mas Dijori, who manages environmental monitoring.
The EPA also did not get its sample from Orange County Sanitation District, said spokeswoman Jennifer Cabral. She said the district discharges treated water from two wastewater plants five miles into the ocean from an outfall plant in Huntington Beach. Cabral said the water discharged into the ocean moves offshore until it is indistinguishable from seawater, and that it does not move onshore to where it might reach swimmers or beach-goers.
"There is no data that we are aware of suggesting that CRE preferentially survive wastewater treatment, or that CRE are more resistant than other bacteria to wastewater treatment employed by OCSD," Cabral said in a written statement.
But University of Minnesota environmental engineering professor Timothy M. LaPara said antibiotic resistant genes can survive standard wastewater treatment processes.
"For whatever reason what comes out of wastewater treatment plants is especially bad, and we don't know why," LaPara said. "Treated wastewater and raw sewage is especially rich in antibiotic resistance. We don't have any specific data about CRE, but, it certainly has elevated levels of resistance even though the same number of bacteria are present."
LaPara said he does not see hospitals as a particular hot spot for CRE. In a study that has not yet been published, he said he found no significant difference in the amount of antibiotic resistant genes (which would include CRE) in the sewage of cities that have lots of hospitals compared to cities that have none.
CDC's direction to hospitals about how best to contain CRE transmission does not call for any specific controls on disposal of human waste.
Two Orange County plants discharge treated and chlorinated waste into the ocean, said Kurt Berchtold, executive officer at the Water Quality Control Board Santa Ana Region. He said he had not heard about the issue of dangerous bacteria in hospital sewage surviving wastewater treatment and ocean discharge. He said wastewater treatment plants are required to have programs to evaluate and monitor "non-domestic sources of discharge into sewer systems, including hospitals and industrial sources." There are also requirements on those sources to inspect and get permits for the waste.
The report was a wakeup call to local, regional and federal water control agencies to start planning to keep dangerous bacteria out of the municipal sewage stream, said James Alamillo of Heal the Bay, a nonprofit advocacy organization that monitors water quality at Santa Monica Bay.
"We need some kind of roundtable to discuss this issue, and come up with a game plan to increase monitoring and ensuring that some threshold is set with regards to the CRE level," Alamillo said.