In-school infection transmission @CPS
We understand that people, including teachers, are afraid. This has been and continues to be a terrible pandemic. But that is why the second thing we have learned in the past months is so important: it is possible to open schools in a way that minimizes risks. Appropriately managed and funded schools, like those in Cambridge, are not major sites of spread. In districts where cities have been unwilling to make reasonable efforts to minimize spread, we understand the reluctance to have in-person schooling. But Cambridge has taken extensive and effective measures. Protocols like mask-wearing, air filtration, ‘bubbled’ classes, distancing and reasonable accommodation of teachers and staff with specific concerns, have meant that Cambridge schools have had near zero transmission. According to its contact-tracing data, Cambridge Public Schools have accounted for 0.7% of the city’s spread (as of December 22, 2020). This means that, as of Dec 22, 99.3% of infection transmission in Cambridge has occurred outside public schools. This fits with the weight of considerable national (also here, here, and here) and international data (also here, here, and here) which shows that schools are not major sites of spread especially when they take even a fraction of the safety precautions that Cambridge has. It is also why we ought to follow the lead of other countries that have prioritized their kids and essential workers by keeping schools open even when there are rising positive cases in the community.
Here are some facts about risk infection control in Cambridge Public Schools.
Ventilation @CPS
The following information about ventilation in Cambridge Public Schools was provided by Jamie Lichtenstein, Ph.D., Senior Affiliated Faculty, Marlboro Institute, Emerson College, Cambridge Public School District COVID-19 Health and Safety Committee Member.
Ventilation is one of several layers of protection for reducing risk of virus transmission. Building ventilation improvements have been made throughout Cambridge Public Schools. Because specific HVAC systems and building designs vary, the improvements have also varied but include ensuring that central ventilation systems have filters in place to keep virus particles from recirculating, maximizing outdoor air in mechanical ventilation systems, repairing or replacing windows to ensure access to outside air whenever possible and adding box fans to classroom windows to increase outside air circulation.
Ventilation is often measured as air changes per hour (ACH). Multiple scientific bodies have recommended schools aim for 4-6 ACH. Cambridge Public Schools has committed to a minimum of 4 ACH in all classrooms. An engineering report showed that the Morse School achieves 4 ACH from existing mechanical ventilation systems without upgrades. All other schools have added portable HEPA air filters to achieve the standard of 4.0 ACH. This means that even during inclement weather, when windows might be closed, those classrooms are at or above an effective 4.0 ACH.
To confirm that all classrooms are meeting those ventilation standards, CPS is measuring classroom CO2. Though multiple things can impact classroom CO2, a general rule of thumb is to keep:
CO2 < 800 ppm @ 4 ACH
CO2 < 650 ppm @ 5 ACH
CO2 < 600 ppm @ 6 ACH
Outdoor air in Cambridge is typically <450 ppm for comparison. CO2 measurements by school and classroom are publicly viewable here.
In general, most classrooms have achieved over 6 ACH. Classrooms are running HEPA filters simultaneously and HEPA filters remove virus but not CO2 and don’t impact the published CO2 measurements.
Recommendations for standardized masking (surgical masks) @CPS
The standardized safety measures implemented in hospitals (non-COVID units) for effective infection control include social distancing, capacity rules, ventilation, hygiene and importantly the mandatory use of standardized surgical masks (at the hospital entrance healthcare workers are required to remove their cloth mask and use a surgical mask).
The safety measures implemented in CPS schools are similar to those implemented in hospitals (non-COVID areas), except that standardized surgical masks are not mandated to CPS staff.
At school pick up, we see several teachers wearing cloth masks.
To achieve safety at the level of healthcare settings, we strongly believe that, rather than cloth masks, staff should use every day standardized (for example surgical) masks to increase safety. CPS owns ~300,000 surgical masks (as of Jan 2021), which would cover the staff needs until the end of the school year and beyond.
We also encourage parents to have their children use surgical masks (15 cents/mask, which can be purchased for example here in child size and adult size).
Here you can find out what a surgical mask is, and here you can find some instructions on how to put the surgical mask on, wear it and take it off (courtesy of Jill Crittenden).
From the lessons learned in previous coronavirus pandemics that hit Korea hard, and from current studies, experts also recommend the use of high quality masks, such as KN95, KN94. There have even increased filtrations and efficiency compared to surgical masks, yet they are more expensive ($ 1.6/mask, reusable) – see next paragraph on Recommendations for high quality masks (KN95/KN94).
Recommendations for high quality masks (KN95/KN94) @CPS
The following masks recommendations were provided by Jill Crittenden, Ph.D., Biomedical Sciences, Scientific Advisor, McGovern Institute for Brain Research at MIT, Member, N95Decon.org, Co-chair, City of Cambridge COVID-19 Expert Advisory Panel, Advisor, Cambridge Public School District COVID-19 Task Force (jrc@mit.edu | 617 576-0162):
Here is a video of mechanical engineer Aaron Collins explaining the largest data set available for mask quality that is relevant to protecting the public. It is based on a standard TSI measurement for how many particles are breathed into a mask when worn (in this case by an adult male).
This researcher’s recommendation is the KF94 (Korean standard for public use) from BeHealthy distributor because it is highly performing, comes in multiple sizes (including adult and child sizes) and is the least expensive ($1.60/mask when purchased in bulk).
For those who want a decorative printed mask that is effective, here is his recommendation: https://masklab.us/
There are many more effective mask options available for purchase from reputable sites, including in child sizes, as you can see here from this mask data summary table. The two key numbers are filtration efficiency (the higher the better) and pressure drop (breathability, the lower the number the better).
Importantly, and not surprisingly based on N95 studies, his data show that repeated wearing does not block filtration. Surgical masks are also safe to rewear because bacteria and fungi do not grow on surgical mask material (they do on cotton). The material prevents water penetration, likely increasing the humidity of air breathed in, to support healthier mucous membrane resistance to infection).
Mask fit is important. If the mask is too loose or too tight, earsavers should be used to adjust the fit (widely available on e-commerce). Most of these masks provide much better fit on the average face than does a flat surgical mask because they go under the chin and far up the nose, in addition to good cheek coverage. This extended coverage is likely to be particularly important while speaking. The importance of fit is exemplified by his test of flat surgical mask Zhushi- without a nose-clip, it has filtration of only 28% and very high breathability; after nose-clip is fastened it has filtration of 78% and lower breathability (now the air cannot simply come in through gaps).
Aaron Collins did not test many cloth masks because they are known to always have poor filtration.
Do you want to use a higher-quality mask but don’t know what kind to buy and what kind will fit snuggly to eliminate gaps and protect you best? Community members are organizing “trial packs” of masks. To order them, please go here.
Cambridge Coalition for Public Education 