More than 50% of bacteria recovered from flying insects in a group of English hospitals were found to be resistant to one or more antibiotics, posing a potential infection risk to patients, according to a study.
“It’s important to take steps to prevent bacteria being brought into hospitals by insects”
The Aston University study collected almost 20,000 insect samples – including houseflies, “filth flies” such as bluebottles and greenbottles and a variety of “drain flies” – from seven NHS hospital sites.
Microbiological analysis found nearly nine in 10 of those tested were carrying potentially harmful bacteria such as E. coli, Salmonella and Staphylococcus aureus, either internally or externally, on their bodies.
Flying insects harbouring bacteria were collected from a number of locations throughout the hospitals using ultraviolet light flytraps, electronic fly killers and sticky traps.
They included areas where food for patients, visitors and staff was prepared or stored, as well as wards, neonatal units and maternity units.
In some cases, the level of bacteria carried by flying insects was enough to potentially cause infection, warned the researchers.
Over three-quarters of the insects collected were “true flies” – a group which includes midges and common houseflies – with a further 14% being “true bugs” including aphids.
“What’s quite interesting is the high proportion of drug-resistant bacteria found in these samples”
Smaller groups of ants, wasps, bees and moths were also collected. The sample collection took place over an 18-month period, with higher numbers being collected in spring and summer.
A total of 86 bacterial strains were isolated from the insect samples, noted the study authors in the Journal of Medical Entomology.
Enterobacteriaceae – the family that includes E. coli and Salmonella – were the most commonly isolated, accounting for 41% of isolations from flying insects.
They were followed by Bacillus – including the “food poisoning bug” B. cereus” – at 24% and staphylococci – including S. aureus, a cause of skin infections, abscesses and respiratory infections – at 19%.
The analysis showed that 53% of the strains were resistant to one or more class of antibiotics. Of this figure, 19% were resistant to multiple antibiotics.
Penicillin was the least effective antibiotic, with many bacteria showing resistance, but resistance to other commonly-administered antibiotics, including vancomycin and levofloxacin, was also seen.
The study was co-authored by PhD student Federica Boiocchi, and Professor Anthony Hilton, both from Aston University, and Dr Matthew Davies, from the firm Killgerm Chemicals Ltd.
Lead author Ms Boiocchi said: “The results from this large-scale microbiological analysis show that a variety of flying insects collected from UK hospitals do indeed harbour pathogenic bacteria of different species.
“What’s quite interesting, though, is the high proportion of drug-resistant bacteria found in these samples,” she said.
She added: “It’s a vivid reminder of how our over-use of antibiotics in healthcare settings is making infections more difficult to treat.”
“It could also mean emphasising the importance of replacing perishable components”
Meanwhile, Professor Hilton highlighted that NHS hospitals were “extremely clean environments” and the risk of insects carrying bacteria and transferring these to patients was “very low”.
“What we are saying in this paper is that even in the cleanest of environments, it’s important to take steps to prevent bacteria being brought into hospitals by insects,” he said.
“NHS hospitals will already be implementing many of these measures, but there are simple steps that can be taken to improve this further,” he noted.
Professor Hilton added: “Infection control is taken extremely seriously in the NHS.
“Insects will only play a very small role in the transfer of bacteria, so this risk should be seen in the context of wider efforts to stop the spread of harmful and drug-resistant bacteria,” he said.
Dr Davies said he hoped the study would prove useful to those in charge of pest management measures, for example by highlighting when insects were likely to be most prevalent.
He added: “It could also mean emphasising the importance of replacing perishable components such as glue boards more frequently, and monitoring the insect catch closely, especially during the warmer months.”