Study Finds Pathogenic Airborne Bacteria Twice as High in Crowded Delhi Areas

Situated within the Indo-Gangetic Plain (IGP), one of the most densely populated and polluted regions in the world, Delhi faces unique meteorological conditions that exacerbate air quality.

 

A new scientific study has revealed that airborne pathogenic bacteria—microbes capable of causing infections in the lungs, gut, mouth, and skin—are found at double the levels in densely populated areas of Delhi compared to less crowded parts of the city. The findings highlight a hidden but serious public health risk in India’s capital, where millions already contend with toxic air pollution.

Delhi’s Unique Risk Zone

Situated within the Indo-Gangetic Plain (IGP), one of the most densely populated and polluted regions in the world, Delhi faces unique meteorological conditions that exacerbate air quality. During winter, the arrival of western disturbances causes sudden temperature drops and a rise in relative humidity. These shifts create stagnant winds and lower boundary layer heights, trapping pollutants close to the surface.

This seasonal cocktail of poor ventilation, high particulate matter, and extreme population density creates conditions ripe for microbial growth and persistence. Past studies have already reported higher airborne microbial populations during winter in the IGP, but the new research goes further by directly linking population density, pollution, and pathogenic bacteria.

The Research Findings

Conducted by scientists from the Bose Institute, an autonomous body under the Department of Science and Technology (DST), the study systematically compared airborne bacterial communities in high-population regions (HPRs) and low-population regions (LPRs) within Delhi.

Key findings include:

• Pathogen levels double in HPRs compared to LPRs.

• PM2.5 particles act as carriers, enabling bacteria to “hitchhike” through the air and penetrate deep into human lungs.

• The bacteria identified are mainly linked to respiratory, gastrointestinal tract (GIT), oral, and skin infections.

• Risk factors peak during the transition from winter to summer, especially on hazy days or after winter rains, when microbes linger in the air longer.

Lead researcher Dr. Sanat Kumar Das explained that PM2.5 particles provide a survival advantage to bacteria, helping them remain airborne and increasing the likelihood of inhalation by humans. Since PM2.5 is small enough to infiltrate the deepest parts of the lungs, it also carries these pathogens further into the body.

Urban Health Implications

Published in the international journal Atmospheric Environment: X (DOI: 10.1016/j.aeaoa.2025.100351), the study could serve as a wake-up call for urban health planning in megacities like Delhi.

The implications are far-reaching:

• Public Health Risks: Millions are exposed daily to not only harmful gases and particulates but also invisible bacterial communities that thrive on polluted air.

• Epidemiology and Outbreak Prediction: Understanding how pollution, weather, and population density influence airborne bacterial communities could help authorities predict outbreaks of respiratory and gastrointestinal diseases.

• Urban Planning: Future city designs may need to integrate air circulation strategies, green infrastructure, and improved sanitation to reduce bacterial spread.

• Healthcare Preparedness: Hospitals and clinics could prepare for seasonal surges in infections linked to airborne microbes.

A Call for Collective Action

The study underscores the interconnectedness of air pollution and public health. While policies often focus on reducing particulate emissions to combat smog, they rarely consider microbial risks embedded within those particulates.

Health experts argue that tackling Delhi’s air crisis must now involve multi-sectoral interventions, including:

• Stricter control of emissions from vehicles, industries, and construction.

• Expanding public awareness campaigns on airborne disease risks.

• Promoting digital and environmental surveillance systems to track bacterial activity.

• Encouraging citizens to adopt protective measures such as masks and indoor air purification, especially during high-risk seasons.

 

The Bose Institute’s findings highlight an invisible dimension of Delhi’s air pollution problem. By revealing that pathogenic bacteria are more abundant in crowded areas, the study sheds light on an urgent need for integrated health and environmental strategies.

As Delhi grows and pollution continues to challenge urban living, recognizing the role of airborne microbes could be key to protecting public health and shaping resilient, future-ready megacities.