The solution to glue ear in kids could lie in healthy nose bugs, scientists say.
The University of Auckland-led study showed, for the first time, that children with glue ear have a different community of nasal bacteria, which is less diverse with higher levels of "bad" bugs, or pathogens, compared to healthy children.
Glue ear, or chronic otitis media with effusion, is where thick fluid gathers in the space behind the eardrum, called the middle ear, for three months or longer.
Around one in 20 preschool children are affected by glue ear at any one time, making it the leading cause of hearing loss in this age group.
By dulling hearing, glue ear can also interfere with language development.
For a long time, scientists believed glue ear did not involve bacteria, and may have been caused by dysfunction in the Eustachian tube, which connects the middle ear to the upper throat and back of the nose.
But many researchers now believe that glue ear, like ear infections, is caused by harmful bacteria invading the middle ear.
An international team led by University of Auckland researchers wondered if the mix of bacteria in the nasal passages may affect the risk of harmful bacteria travelling from the nose to the middle ear and causing glue ear.
The researchers took samples of nose bugs from 73 preschool children with glue ear and 105 healthy children, and compared the type and quantity of bacteria.
"We found that the healthy children had a more diverse community of bacteria in their noses, and high levels of bacteria known to be non-harmful and which may sometimes have health benefits," said study lead author Dr Rebecca Walker, of the university's Faculty of Medical and Health Sciences.
"Viral infections such as colds may disrupt pathogens living relatively harmlessly in the nasal passages, causing them to overgrow and cause conditions such as glue ear."
This suggested that a healthy nasal microbiome may protect against glue ear, she said.
"It may be possible to reduce the risk of bacterial overgrowth through the use of probiotics to shift the balance of bacteria towards the neutral or 'healthy' nose bugs, which could help prevent glue ear developing."
The next step would be to run a randomised, controlled trial to see if probiotics can change the nasal microbiome, and whether this can protect against glue ear.
The study, published in scientific journal Plos One, was co-authored by Auckland researchers Professor Edwin Mitchell, Associate Professor John Thompson and Dr Caroline Walker, and others from Manukau SuperClinic, Massachusetts General Hospital and Harvard Medical School
It was funded by the Brian John Fellowship Trust.