Editor’s note: This story was revised on January 29 to correctly identify one of the influenza strains as H1N1, not H5N1.
A trial that placed adults infected with influenza virus and uninfected people in the same hotel room with limited ventilation but a high air-recirculation rate for two-week stints found no viral transmission, which the authors say provides insight into how to prevent infection.
A University of Maryland (UM)–led research team recruited 11 healthy people with an average age of 36 years (recipients) and five adults with an average age of 21 who were naturally infected with H1N1 or H3N2 influenza (donors) for four, two-week hotel stays in January and February 2024. Participants were assigned to cohort 24b (eight recipients and one donor) or 24c (three recipients and four donors).
The investigators collected exhaled breath, ambient and personal bioaerosols (fine airborne particles containing pathogens), swabs of room surfaces, and blood.
They analyzed samples using digital polymerase chain reaction (dPCR), fluorescent focus assay (used to measure infectious virus particles), hemagglutination inhibition (HAI) assay (used to measure serum antibodies that block viruses from binding to red blood cells), and enzyme-linked immunosorbent assay (used to quantify substances such as antibodies).
The findings were published earlier this month in PLOS Pathogens.
Air purifiers, N95 respirators can help
Donors were observed to cough very little. Relative to previously studied community-acquired flu cases, the team detected viral RNA (44%) and culturable virus (6%) less often and measured fewer viral RNA copies in donors’ exhaled aerosols. Of 23 surface swabs, one was positive for flu on culture.
No recipient contracted a flu-like illness or had serologic evidence of infection or PCR-positive respiratory samples.
Eight of 11 recipients had high concentrations of virus-blocking serum antibodies on HAI, and nine of 11 had stronger binding-antibody responses than donors against vaccine strains corresponding to donor viruses.
No recipient contracted a flu-like illness or had serologic evidence of infection or PCR-positive respiratory samples.
“Potential explanations and insights regarding lack of transmission include importance of cough and seasonal variation in viral aerosol shedding by Donors, of potential cross-reactive immunity in middle-aged Recipients with decades of exposure, and of exposure to concentrated exhaled breath plumes limited by rapid air mixing from environmental controls that distributed aerosols evenly,” the authors wrote.
In a university news release, senior author Donald Milton, MD, DrPH, of UM, said, “Our results suggest that portable air purifiers that stir up the air as well as clean it could be a big help. But if you are really close and someone is coughing, the best way to stay safe is to wear a mask, especially the N95 [respirator].”
Trials over multiple seasons with donors who cough, younger recipients, and environments that preserve normal exhaled breath plumes are still needed, the researchers said.
