Despite in the 1980/90s indicating that hand wash sinks can act as reservoirs of bacteria that cause hospital infections, this risk has been generally dismissed. Since 2000 however there has been an alarming increase in sink-related outbreaks worldwide. This has led Kotay et al from the University of Virginia to carry out a study to see what was happening. They used harmless E. coli bacteria as a surrogate. The bacteria are related to the Klebsiella species that caused an outbreak killed 11 patients at the National Institutes of Health Clinical Center in 2011-2012. The E. coli were genetically engineered to glow green under fluorescent light. so that their dispersion could be easily tracked across five sink modules assembled next to each other in a laboratory
Mathers' team found that the E. coli do live in the sink trap, but they also grew at a steady pace up the side of the pipes and right to the mouth of the drain, forming a sticky biofilm —which adhered to the surface of the pipe and are difficult to wash away. This work found transmission from biofilm growth from the lower pipe to the sink strainer and subsequent splatter to the bowl and surrounding area occurs. The bacteria also splashed out of the sink when water was run — sometimes more than two feet, they found. They also demonstrated that bacterial transmission can occur via connections in wastewater plumbing to neighbouring sinks.
They conclude “This work helps to more clearly define the mechanism and risk of transmission 8 from a wastewater source to hospitalized patients in a world with increasingly antibiotic resistant bacteria which can thrive in wastewater environments and cause infections in vulnerable patients”.
Their experiment helps explain just how such germs cause outbreaks of disease in hospitals. And it also demonstrates just how hard it will be to prevent this kind of spread, because the bacteria are especially difficult to kill when they are growing in pipes.