Airborne influenza virus shedding by patients in health care units: Removal mechanisms affecting virus transmission

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Maintaining high indoor air quality (IAQ) in healthcare facilities is paramount to ensuring the health and safety of patients, staff, and visitors. Recent research has shed light on the distribution of airborne viruses, specifically influenza A/B, in hospital rooms housing patients with confirmed infections. This study not only highlights the presence of these viruses in the air but also explores the various factors influencing their transmission and removal mechanisms. The findings emphasize the need for an integrated approach to control indoor air quality in patients’ rooms, considering both the presence of aerosolized viruses and elevated particulate matter levels.

Airborne Transmission of Influenza Viruses

Influenza viruses, including influenza A/B, are known to spread via respiratory droplets and aerosols. While droplet transmission is highly effective over short distances, aerosol transmission can cover longer distances, posing a significant risk within healthcare settings. Notably, the distinction between droplets and aerosols is not always straightforward, as aerosol particles ranging from 5 to 100 µm can remain suspended in the air for extended periods, potentially leading to infection even beyond close proximity to the source.

Factors Influencing Virus Transmission

Several environmental factors play a crucial role in the transmission of influenza viruses within healthcare units. Temperature (T) and relative humidity (RH) affect the deactivation of viruses, and changes in the air exchange rate (AER) can impact the transport and exposure to air contaminants. Previous studies have attempted to analyze the variability in aerosol distribution and exposure risks, but clear statistical relationships between physical determinants (such as T, RH, AER) and virus concentration in patient rooms have remained elusive.

Research Methodology

This study takes a comprehensive approach to assess airborne virus shedding in healthcare units. Here are the key aspects of the research methodology:

  1. Ethical Considerations: The study received approval from the Institutional Review Board (IRB) at the American University of Beirut Medical Center. Patients provided written informed consent, and their identities remained confidential.
  2. Air Sample Collection: Air samples were collected from single patient rooms with laboratory-confirmed influenza infections. The Coriolis µ Biological Air Sampler was used for this purpose. Samples were collected at two distances from the patient: 0.5 meters and 1 meter, with one room also having samples collected at 1.5 meters to assess RNA detection at greater distances.
  3. Sampling Protocol: During sampling, patients were instructed to face the air sampler to capture expelled viruses effectively. To ensure accurate and unbiased sampling, samples at different distances were collected separately, starting with the nearest distance first (0.5 meters) and then moving to 1 meter.
  4. Environmental Considerations: Sampling equipment was positioned away from ventilation system inlets and outlets to prevent sample loss or cross-contamination. Windows and doors remained closed during the sampling process.

Study Findings and Implications

The results of this study revealed some key findings:

  • Influenza A virus was detected in 42% of the 33 monitored patient rooms, with viruses detectable up to 1.5 meters away from the infected patient.
  • Active coughing by patients significantly contributed to a higher rate of virus detection in collected air samples.
  • Viral load in patient rooms ranged from 222 to 5,760 copies/m3, with an average of 820 copies/m3.
  • Particulate matter (PM2.5 & PM10) levels in most monitored rooms exceeded IAQ daily exposure guidelines.
  • Dispersion and settling were identified as the dominant viral removal pathways, with changes in RH and room temperature influencing viral load removal.

These findings underscore the importance of addressing IAQ in healthcare facilities comprehensively. Ensuring proper ventilation, humidity control, and air filtration can contribute to reducing the risk of viral transmission within patient rooms. Additionally, healthcare facilities should consider implementing measures to minimize particulate matter levels, especially in areas where vulnerable patients are present.


The study on airborne influenza virus shedding in healthcare units emphasizes the need for a holistic approach to indoor air quality management in hospitals. With the ongoing concerns surrounding respiratory virus transmission, including the COVID-19 pandemic, understanding the dynamics of virus aerosolization, dispersion, and removal is crucial. By implementing effective IAQ strategies, healthcare facilities can reduce the risk of viral infections and create a safer environment for patients, staff, and visitors.

Read the full research paper at this link

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