Filthy, deadly: Flies in hospital wards spread drug-resistant bacteria, health experts warn

Hospital wards, meant to be sanctuaries of healing, may also be breeding grounds for drug-resistant bacteria, thanks to an unexpected culprit—flies. New research suggests that these seemingly innocuous insects could be spreading anti-microbial-resistant pathogens among patients, posing a significant threat to global health.

A study conducted by the Ineos Oxford Institute for Antimicrobial Research (IOI) in collaboration with Nigerian researchers has revealed alarming findings: houseflies in hospitals carry bacteria resistant to key antibiotics, including those used as last-resort treatments. This raises concerns over antimicrobial resistance (AMR), a global crisis expected to claim over 39 million lives by 2050.

Scientists collected 1,396 flies from eight hospitals across six Nigerian cities—Abuja, Enugu, Kaduna, Kano, Lagos, and Sokoto—using sticky traps. Analysis of these flies uncovered 17 different bacterial species, including Staphylococcus aureus, a common cause of hospital-acquired infections. Many of these bacteria carried genes linked to antimicrobial resistance.

Although the study does not definitively confirm that flies transmit bacteria to patients, the results are concerning. Dr Chioma Achi, the project lead and co-author of the study, emphasised that the findings strongly suggest flies could serve as vectors for antimicrobial resistance, particularly in tropical low-and middle-income countries where they are abundant.

“Flies are coprophagic—they feed on faeces and waste. In hospitals, they can pick up pathogens from contaminated areas and deposit them on surfaces, medical equipment, or even food, increasing the risk of infection,” Dr Achi explained.

Dr Kirsty Sands, a scientific lead at IOI, reinforced these concerns, stating that flies frequently land on patients and hospital equipment, potentially endangering those with weakened immune systems.

Nigeria ranks 20th among 204 countries for AMR-related deaths, with 263,400 fatalities recorded in 2019 alone. The study published in Environment International builds on previous research in a Pakistani hospital, where scientists found ants, spiders, flies, and cockroaches carrying multidrug-resistant bacteria. Notably, the bacteria detected on these insects were similar to those found in patients’ surgical wounds, suggesting a potential role in spreading infections.

The researchers emphasize the importance of understanding the link between human and animal environments when tackling AMR. Future studies will explore whether insect control measures, such as window screens and bed nets, can reduce hospital-acquired infections and AMR spread.

Antimicrobial resistance is a multifaceted issue that affects human health, food security, and global economies. Hospitals serve as hotspots for drug-resistant infections due to a combination of factors, including patients with pre-existing AMR infections, poor Infection Prevention and Control (IPC) measures, and the misuse of antibiotics.

In low-and middle-income countries, the AMR crisis is exacerbated by limited diagnostic capabilities, inadequate surveillance systems, and insufficient resources for proper hospital sanitation. Tropical climates further compound the issue, as they create ideal conditions for flies to thrive.

Flies are not just a nuisance; they are highly mobile vectors capable of spreading bacteria over significant distances. Research indicates that flies can travel between five to seven kilometers, acting as mechanical carriers of bacteria through regurgitation, defecation, and bodily contact.

Numerous studies have linked flies to the transmission of bacterial diseases, including enterohemorrhagic colitis (E. coli), shigellosis (Shigella spp.) and trachoma (Chlamydia trachomatis).

Despite the growing body of evidence, flies remain largely overlooked in infection control protocols in hospitals.

Flies can harbor antimicrobial resistance genes (ARGs), which enable bacteria to develop resistance to multiple drug classes. In clinical settings, bacteria often exchange these genes through horizontal gene transfer, facilitating the rapid spread of resistance.

Hospitals may inadvertently introduce AMR bacteria through environmental sources, including waste disposal systems and untreated water. Flies serve as intermediaries, picking up bacteria from these reservoirs and transporting them to patient-care areas.

Studies have demonstrated that AMR bacteria found in flies often match those detected in human patients and animals living in the same environments. This suggests that flies play a crucial role in maintaining and amplifying AMR bacterial populations, making them a significant yet underappreciated public health threat.

Kenyan hospitals are not exempt from this crisis. Experts, including Professor Sam Kariuki, Director of the Centre for Microbiology Research at the Kenya Medical Research Institute (KEMRI), warn that flies in hospital settings are exacerbating AMR spread.

“Flies land on contaminated surfaces and pick up bacteria, including drug-resistant strains,” Prof Kariuki explains. “In hospitals where infection prevention and control measures are weak, flies become a major transmission vector.”

Poor sanitation, overcrowding, and inadequate waste management in Kenyan hospitals create ideal conditions for flies to flourish. These insects frequently move between toilets, drainage systems, and patient wards, spreading pathogens like Klebsiella pneumoniae, Acinetobacter, Staphylococcus aureus, and E. coli, all of which exhibit high levels of drug resistance.

Compounding the issue is the practice of empirical antibiotic prescribing, where clinicians administer antibiotics without proper pathogen identification due to limited laboratory testing. This overuse and misuse of antibiotics accelerate resistance development.

Since the World Health Organisation (WHO) declared AMR a global public health emergency in 2015, Kenya has made strides in combating the issue through a One Health approach. The National Interagency Committee on Antimicrobial Stewardship (NASIC) has spearheaded efforts to enhance surveillance and strengthen hospital-based infection control practices.

However, addressing the AMR crisis requires a collaborative effort across multiple sectors. Experts suggest several key strategies:

Enhanced Infection Prevention and Control (IPC) Measures. “Hospitals must enforce strict hygiene protocols, including routine surface disinfection and hand hygiene compliance among healthcare workers,” says Prof Kariuki.

He emphasizes the need to train healthcare professionals on responsible antibiotic prescribing to curb unnecessary use.

Speaking during the 15th Kenya Medical Research Institute (KEMRI) Annual Scientific and Health (KASH) Conference Kariuki said healthcare workers serve as a critical first line of defense, but they can also become vectors for infection transmission if proper precautions aren’t taken. 

“When a healthcare provider becomes infected, they risk transmitting that infection directly to vulnerable patients,” explains Prof Kariuki.

“That’s why we place such emphasis on rigorous hygiene protocols in clinical settings. The consistent use of disinfectants, proper hand-washing techniques, and regular sanitisation aren’t just recommendations—they’re essential barriers that prevent pathogens from moving from healthcare workers or the surrounding environment to patients who may already have compromised immune systems,” he adds. 

According to the researcher, expanding laboratory testing for accurate pathogen identification will reduce inappropriate antibiotic prescriptions.   

He further notes, public awareness campaigns, regulatory enforcement and pest control interventions such as installing window screens, improving waste disposal, and using bed nets, can significantly reduce fly populations in hospitals.

Experts emphasise that combating AMR is not solely the responsibility of healthcare professionals. Patients, caregivers, and the general public have roles to play in reducing the spread of resistant bacteria.

“It’s not a one-person problem, it’s not a one department problem, it’s a problem for all of us. The mother in the village, the father in the village, those who are farmers, those in school – everyone has a role to play in combating antimicrobial resistance.”

Simple steps like covering food, reporting unhygienic conditions in hospitals, and practicing proper hygiene at home can contribute significantly to the fight against AMR.

“Regular handwashing alone can prevent many infections,” he notes. “When combined with better sanitation and fly control, we can significantly reduce the spread of drug-resistant bacteria.”