The current flu season has been notable for the spread of subclade K. A recent study has provided insight into influenza transmission and prevention methods.
Researchers from the University of Maryland conducted an experiment to study flu transmission. Infected college students were placed in a hotel room with healthy middle-aged adult volunteers. No transmission to healthy participants was observed despite close contact.
Dr. Donald Milton, a professor at the University of Maryland's SPH Department of Global, Environmental and Occupational Health, noted the study's finding of no transmission raised questions about flu spread and outbreak control.
The study, published in PLOS Pathogens, is described as the first controlled clinical trial to examine airborne flu transmission between naturally infected and uninfected individuals. Dr. Milton and Dr. Jianyu Lai investigated factors contributing to the absence of infections.
Dr. Jianyu Lai, a post-doctoral research scientist, indicated that coughing significantly increases the likelihood of flu transmission. He noted that infected students, despite having high nasal virus levels, rarely coughed, leading to minimal virus release into the air.
Ventilation was identified as a significant factor. The study room's air was continually mixed by a heater and dehumidifier, diluting airborne virus particles. Additionally, age was considered a protective factor, as middle-aged adults are generally less susceptible to influenza compared to younger adults.
Airborne transmission is widely considered a key factor in flu spread. Dr. Milton stated that robust evidence from randomized clinical trials is necessary for changes to global infection-control guidelines. The research team is continuing to investigate flu spread via inhalation and optimal transmission conditions. The study's findings offer insights into reducing flu season risks.
Dr. Milton suggested that close, indoor, face-to-face interactions in poorly ventilated spaces pose the highest risk. He indicated that portable air purifiers that circulate and clean air could be beneficial. For close contact with coughing individuals, wearing a mask, particularly an N95, was recommended.
Study Methodology
- The study was conducted on a quarantined hotel floor in the Baltimore area.
- It involved five participants with confirmed influenza symptoms and 11 healthy volunteers, split into two groups in 2023 and 2024.
- Participants resided on the isolated floor for two weeks, engaging in routines mimicking social interactions, including conversations and physical activities.
- Infected participants handled shared items that were then circulated among the group.
- Researchers monitored symptoms and collected daily nasal swabs, saliva, and blood samples.
- Viral exposure in participants' breath and the room air was measured.
- Exhaled breath samples were collected using the Gesundheit II machine.
Public Health Context
Limiting flu outbreaks is a significant public health priority. Influenza annually affects up to 1 billion people globally. In the current flu season in the United States, there have been at least 7.5 million cases, 81,000 hospitalizations, and over 3,000 deaths.
Collaborators and Funding
The research involved contributors from UMD's Public Health Aerobiology Lab, UMD Department of Mechanical Engineering, University of Maryland School of Medicine, Icahn School of Medicine at Mount Sinai, the University of Hong Kong, and the University of Michigan. Funding was provided by the NIAID Cooperative agreement U19 grant, the University of Maryland Baltimore Institute for Clinical and Translational Research, the University of Maryland Strategic Partnership: MPowering the State, The Flu Lab, and Balvi Filantropic Fund.