Flies buzzing between beds may be spreading drug-resistant bugs among patients in hospitals, according to new research.
Researchers from the Ineos Oxford Institute for antimicrobial research (IOI) found that houseflies in Nigerian hospitals carry bacteria resistant to some key antibiotics, including those used only as a last resort.
Antimicrobial resistance (AMR), when pathogens such as bacteria and viruses develop resistance to the drugs used to tackle them, is a global threat that is forecast to kill more than 39 million people before 2050. Infections that are picked up by patients while in hospital for other treatments are also a growing concern.
Scientists at the IOI worked with researchers in Nigeria to collect 1,396 flies from eight hospitals in six cities, using sticky traps.
Tests revealed the flies were carrying 17 different species of bacteria, including Staphylococcus aureus, a common cause of hospital-acquired infections. A large proportion of the bacteria sampled had genes linked to antimicrobial resistance.
The nature of the study means that it cannot prove that the flies were spreading the bacteria, but Dr Chioma Achi, the project lead and co-author of the paper, said it was a “very worrying” indicator.
The findings demonstrated that flies “could be vectors for antimicrobial resistance” in hospitals in tropical low- and middle-income countries, where they are “abundant”, she said.
Achi said: “Flies are coprophagic – they eat faeces, they eat manure. Those who have an infection pass it in the faeces, the flies take it up and can perch on the hospital surfaces or even on food, on environments that people touch – so that could be a factor [in the spread of infection].”
Dr Kirsty Sands, scientific lead at the Ineos Oxford Institute for antimicrobial research, and co-author of the paper, said the findings “imply that flies circulating in hospital wards could pose a threat to patients who are vulnerable to infection during their stay, especially as flies commonly land on patients”.
Nigeria ranks 20th out of 204 countries for AMR death rates, with 263,400 deaths linked to AMR in 2019.
The paper, published in the Environment International journal, builds on the team’s previous research in a Pakistan hospital. That study found ants, spiders, flies and cockroaches carrying multidrug-resistant bacteria, and links between those bacteria and those found at patients’ surgical site infections.
Achi said the research demonstrated the importance of considering the connection between human and animal environments in order to tackle the problem of AMR.
The team are planning further research to find out whether insect control methods, such as window screens and bed nets, can lower rates of AMR in hospitals. The Nigerian study also serves as a pilot for a larger multi-country study on insects and AMR in hospitals.
