Just to let people know, any face mask/filtration is better than none. In countries where there are adequate face masks or shortage is not severe, the recommendation from their gov is for public to wear face masks. Only in countries where face masks and respirators are severely lacking, the gov recommends for the public not to wear face masks.
The US Surgeon General and US CDC is telling people that are not healthcare providers (HCP) to not wear face masks claiming it is useless for prevention and actually increases chance of transmission and all we need to do for prevention is to frequently wash our hands with soap. One of their justifications for this official guideline is because of their claim that COVID-19 is not airborne.
The whole logic of respiratory protection is only effective for HCP but not general public (including hospital staff not directly caring for COVID-19 patients) does not make sense, especially when it is proven that wearing respiratory protection will reduce the chance of contracting respiratory viruses. Given the CDC's recent extremely poor credibility in topics related to COVID-19, we can easily see that the reason they are pushing the lie that wearing facemask is not effective and can even increase transmission is simply scare tactics to prevent common people from buying up respiratory protection. Though I don't blame CDC since they are lying with good intention because we need to give our healthcare workers first priority.
The U.S. National Institutes of Health just confirmed that COVID-19 stays airborne through aerosol for 3 hours.
https://www.reuters.com/article/us-...-and-on-surfaces-for-days-study-idUSKBN2143QP
Here is further proof that viral transmissions can be spread through the air. This is just one study that shows influenza, a similar respiratory viral infection can be spread through exhaled infectious aerosols, (viral particles exhaled simply by breathing, talking, singing, or via coughing). These micron sized particles can remain suspended in enclosed spaces and also carried by ventilation systems, which potentially expose everyone who breathes in this same air, such as in stores, fitness centers, hospital and medical clinic waiting areas, churches, schools, concerts, buses, airports, airplanes, and so on.
https://www.medicalnewstoday.com/articles/320690
The Sars Coronavirus in 2003 was found to be transmitted through building mechanical ventilation systems.
https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2004.00317.x
https://www.ncbi.nlm.nih.gov/pubmed/15737151
Europe even has a guide on how to operate building HVAC systems to prevent the spread of COVID-19
https://www.eurekalert.org/pub_releases/2020-03/erc-hto031920.php
Until someone can explain why SARS Coronavirus and Influenza is spread through exhaled breath and through building ventilation systems, and Sars Coronavirus 2 (COVID-19) cannot, I would say we should play it safe especially in enclosed spaces. China asked everyone to wear mask and their success in getting this contained is proof they aren't simply a bunch of idiots. The real reason I see for the different guidance between the US and China is that there is a severe mask shortage in the US whereas China had or could produce enough to meet demand.
"The federal government's Strategic National Stockpile of medical supplies includes 12 million medical-grade N95 masks and 30 million surgical masks — only about one percent of the 3.5 billion that the Department of Health and Human Services estimates would be needed over the course of a year if the outbreak reaches pandemic levels."
https://www.nytimes.com/2020/03/09/health/coronavirus-n95-face-masks.html
Per NYTimes, "the vice president has called on construction companies to donate masks, the surgeon general has urged the public to stop buying them, and experts have warned that, the more doctors and nurses who get sick, the greater strain on a system already stretched thin... Now, doctors, nurses and others are rallying on social media... that members of the public reach out to a nearby hospital if they had masks or other medical equipment to donate"
https://www.nytimes.com/2020/03/19/us/hospitals-coronavirus-ppe-shortage.html
Another study posted on CDC says, "Results of our study have global relevance to respiratory disease control planning, especially with regard to home care. During an influenza pandemic, supplies of antiviral drugs may be limited, and there will be unavoidable delays in the production of a matched pandemic vaccine (31). For new or emerging respiratory virus infections, no pharmaceutical interventions may be available. Even with seasonal influenza, widespread oseltamivir resistance in influenza virus A (H1N1) strains have recently been reported (32). Masks may therefore play an important role in reducing transmission."
https://wwwnc.cdc.gov/eid/article/15/2/08-1167_article
CDC says, "A surgical mask or fit-tested respirator should be worn by healthcare personnel who are within 6 feet of a suspected or laboratory-confirmed influenza patient. A respirator can be selected when antiviral medication supplies are expected to be limited and influenza vaccine is not available, e.g., during a pandemic"
https://www.cdc.gov/flu/professionals/infectioncontrol/maskguidance.htm
CDC says, "HCP should don a facemask when entering the room of a patient with suspected or confirmed influenza. Remove the facemask when leaving the patient's room, dispose of the facemask in a waste container, and perform hand hygiene."
https://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm
In the most recent updated official guidelines for dealing with mask shortages, the CDC now even recommends that medical professionals "might use homemade masks (e.g., bandana, scarf) for care of patients with COVID-19 as a last resort" if other equipment is not available.
https://www.businessinsider.com/cdc-recommends-health-workers-use-bandanas-face-masks-crisis-2020-3