Waste-water treatment by-products, also known as sewage sludge, are frequently used as fertilizer. And that means whatever this stew of sewage leftovers contains, including substances hazardous to human and animal health, could potentially get into the food supply.
According to research just published in the European medical journal Acta Veterinaria Scandinavica, that exact scenario may have already happened. Scientists have recently found antibiotic resistant super bugs in sewage sludge -- and they are sounding the alarm about the danger of antibiotic resistance genes passing into the human food chain.
79 percent tested positive for super bugsLeena Sahlstrom, from the Finnish Food safety Authority, along with a team of scientists from the Swedish National Veterinary Institute, investigated sewage sludge from a waste-water treatment plant in Uppsala, Sweden. The researchers gathered sludge from the plant each week for four months. Out of the of 77 samples collected, 79 per cent of these tested positive for the drug resistant super bugs known as vancomycin-resistant enterococci (VRE).
According to the Centers for Disease Control (CDC), enterococci are bacteria that are normally present in the human intestines and the female genital tract. They can also sometimes be found in the environment. However, if the immune system doesn't keep these germs in balance, enterococci can gain an upper hand and cause infections of the urinary tract, the bloodstream and wounds -- and the resulting illnesses can range from mild to life-threatening.
Vancomycin is an antibiotic long used to treat these infections but some enterococci have become resistant to this drug and evolved into VRE strains. Virtually all VRE infections have become resistant to high levels of several other antibiotics, including ampicillin, too. That means that someone with a serious VRE infection may have to undergo tests to find an antibiotic that will hopefully be effective in treating their specific VRE infection. Although many people recover from VRE infections without any treatment, the CDC notes that some people, especially liver transplant recipients and certain cancer patients, are at particular risk for serious and even fatal VRE infections.
But the risk VRE strains pose by getting into the food supply isn't only related to the possibility people and animals may get infections from them. The Finnish research points out this disturbing possibility: VRE in the fertilizer-used sewage sludge may pass on their resistance genes to other bacteria, creating a host of new super bugs.
"Antimicrobial resistance is a serious threat in veterinary medicine and human healthcare. Resistance genes can spread from animals, through the food-chain, and back to humans. Sewage sludge may act as one link in this chain," Dr. Sahlstrom said in a statement to the media. "Our results demonstrate a need for more efficient hygienic treatment of sewage sludge, in order to avoid possible spread of antimicrobial resistance through use of sewage sludge on arable land."
In another new study recently published in Clinical Biology and Infection, researchers point out that antibiotic resistant infections are on the rise and that VRE infections that get into the bloodstream have a particularly negative impact on death rates, length of hospital stays and medical costs.
