Amid the bustling corridors of Dhaka's hospitals, an invisible danger wafts silently through the air -- drug-resistant bacteria.

A recent study, published in the renowned British weekly scientific journal "Nature", has uncovered alarming levels of multidrug-resistant microorganisms in the air of several hospitals in greater Dhaka, exposing the dangers in healthcare settings.

Speaking to The Daily Star, Abdus Salam, lead researcher of the study, said, "This is very alarming. The bacteria in the air could infect both patients and staffers, leading to hospital-acquired infections [HAIs]. It's especially concerning because these infections are harder to treat with antibiotics."

The study -- "Antibiotic resistance of bioaerosols in particulate matter from indoor environments of the hospitals in Dhaka, Bangladesh" -- was conducted in four hospitals and two ambient locations. It revealed that the particulate matter (PM) -- tiny particles in the air -- carried harmful bacteria that were resistant to several antibiotics.

Samples were collected from Bangabandhu Sheikh Mujib Medical University Hospital, Khwaja Badrudduja Modern Hospital, Dhaka Medical College Hospital, and Monno Medical College Hospital. The data was collected from February to June 2023.

Antibiotic resistance, or antimicrobial resistance (AMR), occurs when a pathogen -- such as a bacterium, parasite, or fungus -- becomes resistant to a specific medication, rendering that treatment ineffective in combating the infection.

The levels of fine particulate matter (PM2.5) at the hospital sites were found to exceed the National Ambient Air Quality Standards for Bangladesh.

Ultra fine particles (such as PM1.0) has the ability to extend the penetration up to the bloodstream through alveoli (air sacs in the lung), capturing the whole body.

The study showed that the PM concentrations at these hospitals were not only higher than national standards but also exceeded the World Health Organization's recommended limits for PM2.5 and PM10 (15 µg/m³). The highest amounts of PM1.0 and PM2.5 were found at Dhaka Medical College Hospital (80.46 ± 11.32 µg/m3; 220.60 ± 16.52 µg/m3), while the highest PM10 concentration was 1452.21 ± 189.78 µg/m3 for sampling point of DMCH. PM2.5 and PM10 can also enter and affect the lungs.

Among the 11 types of bacteria found in the air, including Staphylococcus aureus (Staph), Escherichia coli (E. coli), and Pseudomonas aeruginosa (Pa), many are known to cause serious HAIs like pneumonia, and urinary tract and blood infections.

Alarmingly, most of the bacteria were found to be resistant to multiple antibiotics, making them much harder to treat, the study said.

Various global studies showed that antibiotic resistance has become a significant problem around the world, accelerating at what some scientists say is "an alarming rate", causing an estimated 800,000 additional deaths each year.

The United Nations considers antibiotic resistance a "fundamental threat" to the entire planet's health and safety. "Particulate matter creates the perfect vehicle for bacteria, allowing them to thrive and spread.

This concerning interplay between air pollution and bacterial growth has added a new dimension to the battle against antibiotic resistance," said Salam, also dean of Dhaka University's science faculty.

Antibiotic susceptibility testing revealed that all bacterial isolates (a pure culture of a single species of bacteria that has been identified and separated from other bacteria) from the hospitals were resistant to at least four antibiotics. Some displayed resistance to up to nine.

Ampicillin, azithromycin, erythromycin, and cefixime showed the highest resistance rates, ranging from 81-90 percent.

Health experts warn that for hospital patients, especially those with weakened immune systems, this invisible threat could be the difference between recovery and worsening health.

The study pointed to several factors contributing to the spread of these bacteria, including overcrowded hospitals, outdated building infrastructure, and poor air circulation. Hospitals with old furniture, walls, and flooring were found to harbour more bacteria, allowing them to spread through the air more easily.

Speaking to The Daily Star, Dr Samsad Rabbani Khan, deputy programme manager of the antimicrobial resistance containment programme at DGHS's Communicable Disease Control, said, "We welcome this study as it confirms our perceptions. There's no denying that antimicrobial resistance [AMR] is a worrisome issue globally as well as in Bangladesh. Initially, we were aware of the presence of AMR in humans and animals."

He, however, said the DGHS lacked evidence regarding its existence in airborne environments.

"This study provides critical aspects of AMR's airborne presence in hospital environment, shedding light on a previously unexplored dimension of the problem."

Khan said they are undertaking various activities based on the National Action Plan. "Currently, we are conducting antimicrobial resistance surveillance in the human and animal health sectors. We are in the preliminary stages of developing environmental AMR surveillance."

To overcome the challenge, he suggested the strengthening of infection prevention control and enforcement of antimicrobial stewardship and good clinical practices in all hospitals.