Numerous scientific studies have concluded that two common bacteria that cause colds, ear infections, strep throat and more serious infections cannot live for long outside the human body.
So conventional wisdom has long held that these bacteria won't linger on inanimate objects like furniture, dishes or toys.
However, new research by the University at Buffalo shows that Streptococcus pneumonia and Streptococcus pyogenes do persist on surfaces for far longer than has been appreciated.
"This is the first paper to directly investigate that these bacteria can survive well on various surfaces, including hands, and potentially spread between individuals," senior author Anders Hakansson said.
S pneumonia, a leading cause of ear infections in children and morbidity and mortality from respiratory tract infections in children and the elderly, is widespread in daycare centres and a common cause of hospital infections, said Hakansson.
And in developing countries, where fresh water, good nutrition and common antibiotics may be scarce, S pneumoniae often leads to pneumonia and sepsis, killing one million children every year, he said.
Researchers found that in the day care centre, four out of five stuffed toys tested positive for S pneumonia and several surfaces, such as cribs, tested positive for S pyogenes, even after being cleaned.
The testing was done just prior to the centre opening in the morning, many hours since the last human contact.
Hakansson and his co-authors were interested in the possibility that some bacteria might persist on surfaces when they published work last year showing that bacteria form biofilms when colonising human tissues.
"Bacterial colonisation doesn't, by itself, cause infection but it's a necessary first step if an infection is going to become established in a human host.
"Children, the elderly and others with compromised immune systems are especially vulnerable to these infections," he said.
The experiments found that month-old biofilm of S pneumonia and S pyogenes from contaminated surfaces readily colonised mice, and that biofilms survived for hours on human hands and persisted on books and soft and hard toys and surfaces in a daycare centre, in some cases, even after being well-cleaned.
"In all of these cases, we found that these pathogens can survive for long periods outside a human host," said Hakansson.
The study was published in the journal Infection and Immunity.