A Restaurant That Was Poorly Ventilated
The conclusion of the study revealed that COVID-19 became spread by a mix of aerosol exposure that reached past a 2 m distance (extended airborne short-range) and close contact (droplet exposure within 7 feet). Lackluster ventilation resulted in minimal virus dilution, which was regarded as a notable factor. The study was inconclusive, and couldn’t determine how relevant airborne transmission was (because of the HVAC’s atypical configuration). Insufficient customer infections in certain adjacent zones indicated that COVID-19 was isolated, stopping transmission of disease. Because waiters weren’t infected, the indication is that contact of a short-term nature was not enough for COVID-19 transmission.
A Bus That Was Poorly Ventilated
126 people had taken a trip to China in a couple of buses, both of which had an AC system that had recirculating air (but no exterior air). An individual that was infected – who originated from Wuhan – happened to be on 1 of the 2 buses. Each passenger with close contact with the individual was infected, along with more than 170 other patrons who hadn’t set foot on that bus. Of them:
- Zero bus passengers that the individual infected didn’t end up contracting COVID-19.
- 7 attendees that hadn’t been on the bus ended up contracting the virus. However, they were in very close proximity to the individuals that became infected at an event everyone attended.
- 23 bus riders that were on the same vehicle with the individual infected had contracted the virus. As far as location goes, more cases of infection happened with individuals who sat more than 7 feet away from the Wuhan-based traveler.
A Conference Center That Was Poorly Ventilated
Thirty people went on a 3-day trip to China. A person from Wuhan that happened to be infected within the same building, which happened to have significantly poor ventilation (for instance, HVAC was cycled on for 15 minutes only every 4 hours). What wasn’t established was who was in close range with the individual infected, so determining who was within the droplet range was not possible. 15 attendees later became infected. Investigators believe that several infections happened because of airborne exposure. They came to this conclusion after contrasting this incident’s infection rate directly to outbreaks that were similar. One major contributor seem to be poor ventilation, which impacted effective dilution.
Study Samples of COVID-19
A Cruise Ship That Was Well Ventilated
An epidemiological evaluation of 696 SARS-CoV-2 cases that took place on the cruise ship known as “Diamond Princess” offered a chance to investigate the effectiveness of an HVAC system recirculating air. It was said to be running with a ventilation rate that adhered to ASHRAE standards. Classification of infection rates fell into a few categories:
- People engaging without restrictions (for instance, passengers before being quarantined).
- Passengers that were quarantined within their respective cabins without any COVID-19 positive people present.
- Passengers that were quarantined in cabins who were exposed directly to infected individuals.
Infections occurred only in the first two classifications. Passengers that were quarantined inside of a cabin were not infected because of recirculated air coming from areas that infected people were in. Because there were no cases in the second category, the assumption is that dilution and circulation of air – by way of HVAC systems – didn’t contribute to infection.
A Call Center in Korea
There were 1145 occupants of a building that received COVID-19 tests. Several cases were discovered on a single floor – a popular call center that was densely occupied. 44% of employees there had tested positive. 94% of people who received positive test results were situated in one portion of that building. 5 cases were discovered on the remainder of a floor where most employees worked out of. Contact that transpired between occupants on the floor’s affected side happened to be quite short. Uniform spread that transpired throughout the area infected indicates that airborne transmission was a factor. There wasn’t sufficient information provided to establish any relationship between HVAC zoning and case location.
Other studies sampled the virus on surfaces and in the air, but they didn’t correlate with these infection patterns. Measured concentrations of contaminants determined that airborne exposure was significantly away from individuals infected, but it did not determine if that exposure transmitted infection to other people.
A Hospital in Oregon
Surfaces were evaluated for COVID-19 within an HVAC system. The recirculating system was placed in rooms that had SARS-CoV-2 patients. Sites that had positive examples included a pre-filter, which received mixed air (outside and return), as well as supply air dampers, post-filtration. Results that were recently reported established that COVID-19 was capable of being transmitted through an HVAC system. These findings didn’t establish if COVID-19 remained infectious (airborne viruses gradually inactivate themselves). Air-quality also wasn’t tested.
Two Hospitals in Wuhan
Airborne COVID-19 was tested at a couple of hospitals in China, as were outdoor locations nearby. Investigators classified several samples as per their particle size, as well as their predicted surface deposition rate.
- Airborne detection of the virus was prevalent in a majority of sites that had patients present.
- Airborne concentrations that were elevated were discovered in one bathroom (possible fecal contribution).
- In a temp hospital, concentrations happened to be lower. Air filtration here was much greater in comparison to a long-term hospital.
- Deposition tests linked fomite contamination with particle settling.
- Viruses that were airborne settled on various surfaces that were outside of the immediate space around the source. They were subsequently re-suspended, which contributed to the airborne exposure further.
- Elevated concentrations of air were quantified in an employee changing area. PPE (personal protective equipment) was used, indicating settled virus resuspension.
- Concentrations were much lower in employee changing areas after implementation of rigorous sanitization practices.
- Distribution of particle sizes varied. Droplets greater than 1 µm were dominant at one particular site. Airborne particles lower than 1 µm dominated another. There was another site that was divided equally between small particles and droplets.
Airborne particles 7 feet away (or more) from patients were discovered inside an adjacent hall in a study recently. COVID-19 wasn’t detected in air surrounding infected patients situated in Iranian and Singapore hospitals. There wasn’t enough information to establish if negative outcomes were because of methodological limitations.
For infectivity’s sake, a virus that was similar to COVID-19 was generated artificially before being measured. Detection of this infectious virus happened after a few hours of it being airborne. On surfaces, detection occurred after three days. Another study discovered infectious airborne viruses after a dozen hours.
These sampling studies are representative of occupant exposure, however, disease transmission is not necessarily clear. PCR (polymerase chain reaction) is what most of the analyses were based on, as it measured COVID-19 RNA totals. That included inactivated viruses no longer capable of causing infection. Methods used measured infectious viruses only.