Crowded Public Spaces as Hotspots of Airborne Microbial Risk: A Population-Weighted Risk Assessment in Urban...

Area of Science:

• Environmental microbiology
• Urban public health
• Infectious disease epidemiology

Background:

• Airborne pathogens and antimicrobial resistance (AMR) present increasing urban health threats.
• High-occupancy public spaces (HOPS) may amplify pathogen persistence and dissemination due to enclosed environments and high population density.
• The microbial load and associated risks in HOPS are not well understood.

Purpose of the Study:

• To compare bioaerosol characteristics in various urban environments, including crowded public spaces (CPSs), waste collection facilities (WCFs), and an urban air monitoring site.
• To assess the contribution of human sources to airborne bacteria and AMR in CPSs.
• To evaluate the population-weighted infection burden (PWIB) of airborne microbes in urban settings.

Main Methods:

• Culture-based and molecular analyses of bioaerosols.
• Source-tracking to identify microbial origins.
• Risk assessment using a novel population-weighted infection burden (PWIB) metric.
• Comparison across university cafeterias, subway stations, WCFs, and an urban air monitoring site.

Main Results:

• CPSs exhibited culturable bacterial and AMR burdens comparable to WCFs, significantly exceeding those at the urban air monitoring site.
• Human-associated sources accounted for approximately 50% of airborne bacteria in CPSs.
• Multidrug-resistant isolates, high-risk beta-lactam antimicrobial resistance genes (ARGs), and clinically relevant pathogens were enriched in CPSs.
• Despite similar contamination levels to other hotspots, CPSs contributed more to city-scale infection burden due to high population exposure.

Conclusions:

• Urban airborne microbial risk is influenced by both contamination intensity and human occupancy patterns.
• CPSs are significant reservoirs for airborne bacteria and AMR, comparable to conventional hotspots like WCFs.
• Integrating human activity into microbial risk assessments is crucial for understanding urban health risks in high-density environments.