S. Mehtar asks
This information is very useful to us in countries where there is little ventilation in clinical areas. It is indeed very helpful.
I have another question which I hope the group can help me with.
Do we know how much spread can be contained by the person who is infected wearing a face mask? In other words can we reduce the number of bacilli by covering our mouth when coughing. And if so, by how much?
I can't find any literature on this.
The reason that you have not found the answer is that there have been no studies. The use of surgical masks to reduce airborne spread goes back to the 1918 flu pandemic, and they were thought to be effective, but no hard evidence was obtained.
It is not published yet, so I cannot publish too much here, but we have asked our MDR patients at the AIR Facility in Witbank to wear surgical masks every other day. On the days they wore them, exhaust air from the ward went to one guinea pig exposure, and on the days that they did not wear them, it went to a second guinea pig exposure chamber. We did this over a 3 month period. Nurses reminded patients to wear their masks 7 AM to 7 PM, and we only sampled air during that period, feeling that asking patients to wear masks when they slept was not reasonable.
The result was a consistent 50% reduction in the number of guinea pigs infected when patients wore surgical masks. This compares to an 80% reduction when upper room UV was used every other day. This is about what I would have expected, and this is under study conditions, that is, nurses reminding patients to wear the mask. Under routine clinical conditions I would predict even less efficacy, especially if patients are asked to wear them more or less all the time - except when eating, etc. Ideally, the surgical mask is most useful short-term in untreated, symptomatic patients when they can be reasonably expected to comply. For example, while in the waiting room, or in radiology waiting for a chest x-ray, etc, etc. Long term it is hard to wear a surgical mask continuously, and the results, despite reminders show that.
I do not think that better masks are the answer, since no mask or respirator can contain the force and volume of a cough - there will be leakage. We are asking the surgical mask to act as a barrier, like a tissue or hand, stopping large particles before they can evaporate into smaller particles and pose a threat. Surgical masks do that, but the result is a maximum of 50% reduction based on our studies - which will be published.
Edward A. Nardell, MD
Harvard Medical School (Medicine; Global Health and Social Medicine)
Harvard School of Public Health (Environmental Health; Immunology and Infectious Diseases)
Brigham and Women's Hospital
Division of Global Health Equity
FXB Building, 709c
651 Huntington Ave.
Boston, MA 02115