Drug-resistant bacteria found on hospital insects

More than 50% of bacteria recovered from flying insects in a group of English hospitals has been found to be resistant to one or more antibiotics, posing a potential infection risk to patients.

Over an 18-month period, researchers from Aston University collected almost 20,000 insect samples from seven NHS hospital sites. Flying insects were collected from a number of locations throughout the hospitals, including areas where food for patients, visitors and staff was prepared or stored as well as wards, neonatal units and maternity units. Higher numbers were collected in spring and summer, with the full results published in the Journal of Medical Entomology.

Microbiological analysis found that nearly nine in 10 of those insects tested were carrying potentially harmful bacteria — either internally or externally on their bodies — with a total of 86 bacterial strains isolated from the samples. Enterobacteriaceae — a family that includes E. coli and Salmonella — were the most commonly isolated, accounting for 41% of isolations from flying insects, followed by Bacillus (which includes the ‘food poisoning bug’ B. cereus) at 24% and Staphylococci (which includes S. aureus, a cause of skin infections, abscesses and respiratory infections) comprising 19%. In some cases, the level of bacteria carried by flying insects was enough to potentially cause infection.

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 found to be the least effective antibiotic, with many bacteria showing resistance. Resistance to other commonly administered antibiotics, including vancomycin and levofloxacin, was also observed.

“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,” said Federica Boiocchi, lead author on the study.

“What’s quite interesting, though, is the high proportion of drug-resistant bacteria found in these samples. It’s a vivid reminder of how our overuse of antibiotics in healthcare settings is making infections more difficult to treat.”

Study co-author Anthony Hilton added: “NHS hospitals are extremely clean environments and the risk of insects carrying bacteria and transferring these to patients is 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. NHS hospitals will already be implementing many of these measures, but there are simple steps that can be taken to improve this further.

“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.”

Dr Matthew Davies, of Killgerm Chemicals, said: “We hope this study is useful for those in charge of pest management measures, for example, by highlighting when insects are likely to be most prevalent and which are of the greatest risk to public health, therefore informing the selection of quality insect monitors and effective UV light traps to be installed, among other integrated pest management measures provided by professionals.

“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.”

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