In air conditioned environment these large droplets may travel farther.
However, ventilation — even the opening of an entrance door and a small window can dilute the number of small droplets to one half after 30 seconds. (This study looked at droplets from uninfected persons). This is clinically relevant because poorly ventilated and populated spaces, like public transport and nursing homes, have high SARS-CoV-2 disease transmission despite physical distancing. https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30245-9/fulltext
Objects and surfaces
Person to person touching
The CDC’s most recent statement regarding contracting COVID-19 from touching surfaces: “Based on data from lab studies on Covid-19 and what we know about similar respiratory diseases, it may be possible that a person can get Covid-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose or possibly their eyes,” the agency wrote. “But this isn’t thought to be the main way the virus spreads. https://www.cdc.gov/media/releases/2020/s0522-cdc-updates-covid-transmission.html.
The surfaces where tested with the PCR (polymerase chain reaction) test, which greatly amplifies the viral genetic material if it is present. That material is detectable when a person is actively infected. This is thought to be the most reliable test.
Computer mouse (ICU 6/8, 75%; General ward (GW) 1/5, 20%)
Trash cans (ICU 3/5, 60%; GW 0/8)
Sickbed handrails (ICU 6/14, 42.9%; GW 0/12)
Doorknobs (GW 1/12, 8.3%)
81.3% of the miscellaneous personal items were positive:
Medical equipment (spirometer, pulse oximeter, nasal cannula)
PC and iPads
Cellular phones (83.3% positive for viral RNA)
Remote controls for in-room TVs (64.7% percent positive)
Toilets (81.0% positive)
Room surfaces (80.4% of all sampled)
Bedside tables and bed rails (75.0%)
Window ledges (81.8%)
Plastic: up to 2-3 days
Stainless Steel: up to 2-3 days
Cardboard: up to 1 day
Copper: up to 4 hours
Floor – gravity causes droplets to fall to the floor. Half of ICU workers all had virus on the bottoms of their shoes
Filter Efficiency and Fit
*Data from a University of Illinois at Chicago review
HEPA (high efficiency particulate air) filters – 99.97 – 100% efficient. HEPA filters are tested with particles that are 0.125 μm.
Masks and respirators work by collecting particles through several physical mechanisms, including diffusion (small particles) and interception and impaction (large particles)
N95 filtering facepiece respirators (FFRs) are constructed from electret (a dielectric material that has a quasi-permanent electric charge. An electret generates internal and external electric fields so the filter material has electrostatic attraction for additional collection of all particle sizes. As flow increases, particles will be collected less efficiently.
Known patients infected with SARS-CoV-2 wore masks and coughed into a Petrie dish. “Both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface.”
Overall, data were collected from 714 men and women. About half the sample were women and all adult ages were represented. Only 90 participants (12.6%, 95% CI 10.3%-15.3%) passed the visual mask fit test. About three-quarters performed strap placement incorrectly, 61% left a “visible gap between the mask and skin,” and about 60% didn’t tighten the nose-clip.
*A 2011 randomized Australian clinical trial of standard medical/surgical masks
“Advice to decision makers on the use of masks for healthy people in community settings
As described above, the wide use of masks by healthy people in the community setting is not supported by current evidence and carries uncertainties and critical risks.”
“Medical masks should be reserved for health care workers. The use of medical masks in the community may create a false sense of security, with neglect of other essential measures, such as hand hygiene practices and physical distancing, and may lead to touching the face under the masks and under the eyes, result in unnecessary costs, and take masks away from those in health care who need them most, especially when masks are in short supply.”
“Masks are effective only when used in combination with frequent hand-cleaning with alcohol-based hand rub or soap and water.”
WHO acknowledges that most people do not use masks properly.
Dr. Nancy Messonnier, director of the Center for the National Center for Immunization and Respiratory Diseases:
In March 5, 2019 regarding the flu: “Masks are not usually recommended in non-healthcare settings; however, this guidance provides other strategies for limiting the spread of influenza viruses in the community:
cover their nose and mouth when coughing or sneezing,
use tissues to contain respiratory secretions and, after use, to dispose of them in the nearest waste receptacle, and
perform hand hygiene (e.g., handwashing with non-antimicrobial soap and water, and alcohol-based hand rub if soap and water are not available) after having contact with respiratory secretions and contaminated objects/materials.
“We know that wearing a mask outside health care facilities offers little, if any, protection from infection. Public health authorities define a significant exposure to Covid-19 as face-to-face contact within 6 feet with a patient with symptomatic Covid-19 that is sustained for at least a few minutes (and some say more than 10 minutes or even 30 minutes). The chance of catching Covid-19 from a passing interaction in a public space is therefore minimal. In many cases, the desire for widespread masking is a reflexive reaction to anxiety over the pandemic.”
Surgical masks – loose fitting. They are designed to protect the patient from the doctors’ respiratory droplets. The wearer is not protected from others airborne particles
People do not wear masks properly. Most people have the mask under the nose. The wearer does not have glasses on and the eyes are a portal of entry.
The designer masks and scarves offer minimal protection – they give a false sense of security to both the wearer and those around the wearer. **Not to mention they add a perverse lightheartedness to the situation.
If you are walking alone, no mask – avoid folks – that is common sense.
Remember – children under 2 should not wear masks – accidental suffocation and difficulty breathing in some
If wearing a mask makes people go out and get Vitamin D – go for it. In the 1918 flu pandemic people who went outside did better. Early reports are showing people with COVID-19 with low Vitamin D do worse than those with normal levels. Perhaps that is why shut-ins do so poorly. https://www.medrxiv.org/content/10.1101/2020.04.08.20058578v4