Let's Stop Hand Hygiene Theater and Focus on Airborne Transmission

Judy Stone, MD


December 21, 2021

Any lingering thoughts that SARS-CoV-2 transmission is not by air should finally be gone. Two recent cases put the nail in the coffin of hand hygiene theater.

A recent definitive case of COVID-19 transmission occurred in a Hong Kong quarantine hotel. Patients A and B had both been doubly vaccinated, and both had a negative reverse transcription PCR (RT-PCR) for SARS-CoV-2 within 72 hours before their arrival. Patient A arrived from South Africa on November 11, 2021. Patient B came from Canada on November 10. Both stayed in the Regal Airport Hotel, and their rooms were on the same floor, directly across from each other.

Patient A was asymptomatic but had a positive PCR on November 13. Patient B developed mild symptoms on November 17 and tested positive the next day. None of the other quarantined people on that floor tested positive, nor did the hotel's staff.

The viral genomes from these two positive cases differed only by one nucleotide, ie, minimal variation.

The investigation — including closed-circuit television camera footage — showed that neither case-patient broke the quarantine by leaving their rooms. No other people entered their rooms, and no items were shared by them. The patients only opened their doors to pick up trays for their meals and to have RT-PCRs done every 3 days. That testing was not on the same days.

The investigation ― published in Emerging Infectious Diseases ― concluded that "airborne transmission across the corridor is the most probable mode of transmission."

It is also reported that the Hong Kong health department said that the hallway had "unsatisfactory" air flow. They also noted that the source patient, who traveled from South Africa, sometimes either did not wear a mask when retrieving his meals or wore a mask with a valve.

Yuen Kwok-yung, a leading microbiologist at the University of Hong Kong and COVID-19 policy expert for the government, called using valve-equipped face coverings "a bit selfish," per the South China Morning Post. He blamed the masks for the transmission.

Subsequently, the government's Centre for Health Protection banned valved masks and urged the use of surgical masks alone. They say that the exhaled breath is not filtered by the valve.

While this is a commonly held belief, a recent NIOSH (National Institute of Occupational Health and Safety) study contradicts this idea. The researchers' findings were based on tests of 13 filtering facepiece (FFR) models from 10 different manufacturers. They found that "FFRs with an exhalation valve provide respiratory protection to the wearer and reduce particle emissions to levels similar to or better than those provided by surgical masks procedure masks, or cloth face coverings."

What is the likely reason for this surprising finding? Presumably, this is because surgical masks leak significantly around the sides and valved masks fit more securely. This is also why the current mask recommendation is that, if you don't have access to an N95, KN95, FFP or similar, you wear a surgical mask under a more tightly shaped and fitted cloth mask.

A Second Case

A second quarantine case similar to the one in Hong Kong occurred last year in New Zealand.

Genomic and epidemiologic data helped solve this outbreak investigation. Here, too, CCTV confirmed no violation of the quarantine.

A review of the ventilation showed that the rooms were net positive pressure compared with the corridor, allowing air to enter the hallway from the guest rooms.

Ultimately, nine patients were involved in this outbreak. In one cluster, "there was a 50-second window between closing the door to the room of case-patient C and opening the door to the room of case-patients D and E."

So, this was an earlier probable case of aerosol transmission without direct person-to-person contact, which did not get much attention.

Ian Mackay, PhD, is a virologist, educator, and author of the highly informative Virology Down Under blog. Mackay told Medscape, "Australia saw multiple examples of 'escape' into the community of virus from infected travelers in hotel quarantine ― initially because of a failure to prevent aerosols or because of a lack of understanding that they were the main route of transmission."

He said, "this has been controlled much better in recent months."

So why do some experts seem surprised by these findings? After all, almost 20 years ago, a physician who was mildly ill with flu-like symptoms checked into the Hotel Metropole in Hong Kong to attend a wedding ― and he triggered a global outbreak, subsequently identified as SARS.

Seventeen other guests on that physician's floor later became infected. Studies showed that the guest rooms were all positive pressure to the hallway. One guest triggered an outbreak in Toronto after she flew home from Hong Kong. Others spread SARS to Singapore and Vietnam. Mysteriously, no hotel staff became infected, nor did guests on other floors.

The Ongoing Debate

How SARS is spread is still debated.

The World Health Organization (WHO) says it is an airborne virus that spreads through small droplets. The Centers for Diseases Control and Prevention (CDC) says, "The primary way SARS appears to spread is by close person-to-person contact...and droplet spread" and by fomites (touching infected objects).

The CDC adds that it is "possible that SARS-CoV might be spread" through the air.

There was a large outbreak recently among people who attended a Christmas party at an Oslo restaurant. At least half of the 120 participants are estimated to have become infected with the new Omicron variant at the party. Two of the attendees had recently returned from South Africa.

According to Reuters, all attendees were vaccinated and had tested negative before attending an energy company's end-of-year party.

The Norwegian Institute of Public Health reports that as of December 8, 2021, 70% of attendees have been diagnosed with COVID-19. Most reported symptoms developed within 3 days. They expect most will be confirmed as having the Omicron variant.

Notably, more than 60 other patrons who visited another part of the restaurant that evening, but did not attend the party, also have COVID.

For other examples supporting airborne transmission of COVID-19, see this extensive thread by Jose-Luis Jimenez, PhD, an aerosol expert at the University of Colorado, explaining how to avoid transmission of the virus:

On February 2, 2021, an editorial in Nature stated, "There's too much focus on surfaces" and asked CDC and WHO to update their guidances.

There are also two telling tweets from Kimberly Prather, PhD, professor and director of the CAICE (Center for Aerosol Impacts on Chemistry of the Environment) at UC San Diego. They show that the CDC and WHO scientists were on the verge of declaring COVID-19 as having airborne transmission in February 2020:

Asked why WHO and CDC are still denying that COVID-19 is solely airborne, Jimenez told Medscapethat this largely goes back to some of the teachings of infectious disease transmission, beginning with an error from the public health pioneer Charles Chapin in 1910, who claimed that contact was the main source of respiratory transmission and droplet transmissions were included as part of contact spread.

Don Milton, MD, DrPH, professor of environmental health at the University of Maryland and expert on the aerobiology of respiratory viruses, also traced the origin of misunderstanding back to Chapin.

"There is a deeply held belief in much of the infectious disease professionals, that if you use the word 'airborne,' you will scare people and then they will freak out and not do anything that you want them to do," he told Medscape.

While the CDC is now encouraging masking indoors if in areas of high COVID transmission, their waffling message has confused the public and raised mistrust.

Many people do not understand that they still need to mask even though they are fully vaccinated. Too many believe they have been lied to and don't accept that recommendations change as we learn more. There is still too much emphasis on sanitizing surfaces.

It would help if, instead, the CDC and WHO stressed improving ventilation and provided everyone with high-quality masks, as well as intensive education about how to wear masks. In addition to universal vaccination, the CDC and WHO need to clearly state, "COVID has airborne" transmission, and advise accordingly.

Jimenez, Mackay, and Milton report no relevant financial relationships.

Judy Stone, MD, is an infectious disease specialist and author of Resilience: One Family's Story of Hope and Triumph Over Evil and of Conducting Clinical Research, the essential guide to the topic. You can find her at or on Twitter @drjudystone.

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