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Repeated Usage of Mask Protection

By Inge Corless | 17 Mar, 2010 Last edited by Julia Fischer-Mackey on 13 May 2010

Dear All,

I have been following the discussions on the protection afforded by various types of masks. When I visited some MDR TB units in South Africa, I was given an N95 respirator which they promptly hung on a hook or placed in a desk drawer at the end of my visit. That struck me then as it does now that I was treated as a guest and provided with their safest equipment. I wondered how safe the masks are that are used repeatedly- some on a daily basis for a month. I observed nurses wearing surgical masks. The 2009 WHO policy on TB infection control in health care settings, congregate settings, and households (http://www.ghdonline.org/ic/resource/who-policy-on-tb-infection-control-in-he...) indicate they don't know, when "administrative and environmental controls are in place", the added value that particulate respirators provide beyond the safety of the surgical masks that are frequently used by hospital staff in resource-limited countries.

Do we know how safe surgical masks worn repeatedly are? It strikes me that if we don't have data on masks as used in practice, this is an area worthy of further investigation.

Thank you for your consideration.



Edward Nardell, MD Moderator Replied at 4:20 PM, 17 Mar 2010

Hi Inge,

There is so much we don't know. The evidence base for most of the WHO recommendations are lacking and the studies extremely difficult to imagine much
less carry out. We are left with applying principles from particle testing of respirators and masks, assumptions from fit testing, etc.

Moreover, exposures in high risk settings are commonplace, not just when you expect it and are
wearing a mask or respirator.

The biggest flaw in respirator use is face seal leak - a minimum of 15-20% even with a new, fit-tested respirator. So, right of the bat, don't expect perfect protection from a disposable respirator. Reusable respirators can fit better
and are cheaper in the long run, but have not been designed for clinical use as yet.

Having said all that, a poor fitting mask that only reduced exposure by 50% would have a protective effect equivalent to doubling ambient ventilation -
which is hard to do, So, masks and respirators, although imperfect, have substantial value.

The most common question we get is, "how long can I reuse a disposable respirator"? This is because they are expensive. The answer that one
respirator expert gives is, as long as it is structurally intact and the elastic bands aren't "too" loose. This is a subjective call. It depends how often and how it is put on and off, the quality of the elastic, etc. If you err on the side of too long the protection, already imperfect, will be less - but not none.

I am also concerned with reused respirators as fomites for every other common hospital bacteria that are passed by contact, from staph to c difficile. At least many reusable respirators have a smooth surface that can be wiped off with

I never recommend use of surgical masks for protecting workers from TB, although they are fine as droplet barriers for infectious patients. Their use in flu is apparently to interrupt direct inoculation - not for airborne protection.


Inge Corless Replied at 4:22 PM, 17 Mar 2010

Dear Ed,

Thank you for your useful review and for getting back to me so quickly. My observations were of the reuse of surgical masks and I  thought we could develop an approach to sampling the interior of the mask on a daily basis at the beginning and end of a nurse's shift and see what we can grow out and when.

Given that these masks may be used for as long as a month or more we will be able to obtain a picture of the protection afforded providers over this period of time. Such data may give us the basis for making recommendations.  By using surgical masks rather than respirators, we won't be in the fit debate and we're testing the situation as it obtains in many resource-limited settings. In addition, it would make sense to examine the epidemiological data on institutions where more of the health care providers develop Tb which is not to say that the transmission occurred in the health care setting.  In fact, if we can find two institutions- one with high rates and one with low rates we could learn a lot. Perhaps you've already done this.

Please forgive my ramblings. I see a problem and think about how one might go about investigating it. All the Best, Inge

Edward Nardell, MD Moderator Replied at 4:26 PM, 17 Mar 2010

I do not believe your study will work. If TB is the issue, it cannot be cultured from the inside or outside of masks. The concentrations in air are extraordinarily low and the concentrations of more rapidly growing personal and environmental organisms very, very high. What will grow on the inside of masks are the wearers own mouth flora.

Finally, workers ought not be using surgical masks as protection from TB, as noted below. Most places I have visited know this and are trying to use respirators. Masks should be discouraged.

Inge Corless Replied at 4:31 PM, 17 Mar 2010

Dear Ed,

Thinking about your comments I've done some further investigation on the NIOSH site and elsewhere. Although droplets are rapidly evaporating, some remain suspended in the air. Clearly infectiousness
declines with treatment. In the early days of HIV/AIDS, the conventional wisdom was that HIV particles would not be viable on counters, etc. There was data that HIV survived on counters for three days and longer if the counters were wet. The situations of health care providers (and particularly those with frequent close contact) don't mimic the research conditions which generally specify general size dimensions and don't take into consideration proximity to the source of the contamination. Thanks you for taking the time to consider these remarks. Inge

Edward Nardell, MD Moderator Replied at 4:33 PM, 17 Mar 2010

The issue with TB is very specific to its mode of transmission and pathogenesis. Yes, lots of large particles are generated and may be inhaled. However, the respiratory tract is not susceptible to TB, except at the alveolar level because TB is an infection of the alveolar macrophage. Ironically, it has evolved to require the environment inside the macrophage to grow and replicate, initiating infection. Bovine TB, of course, is adapted to ingestion, but human TB has a very narrow ecological niche. Rarely it is inoculated into the skin and a local granuloma forms, but the normal pathway is through the alveolar macrophage, which requires particles in the 1 - 3 um range, i.e., airborne droplet nuclei. Except as sources of dried droplet nuclei, large particles with TB are unimportant since TB cannot be acquired from surfaces even if it remains viable. Touching eyes and mouth, etc, will not transmit human TB. Proximity to the source increases the local concentration of droplet nuclei before dilution in air, and increases the risk of transmission in that way, but it does not imply that large droplets play a role. Just food for thought.

Inge Corless Replied at 4:39 PM, 17 Mar 2010

Dear Ed, You always give me more than enough food for thought. I appreciate the feast. I go back to the literature after every communication. I also think about what I observed in Durban, South Africa and Chennai, India. Providers wear masks, and in some cases surgical masks, but the evidence base for the latter according to WHO is inadequate. There seems to be considerable research on N95 respirators but less on surgical masks and none that i found in vivo. Conducting any research is complicated by the high endemic TB rate. Consequently, it becomes a challenge to distinguish the source of the infection in health care workers- whether community or health care setting.

So the question becomes how do we move the field forward?  How do we protect health care providers particularly  from MDR TB in resource-limited settings where N95 respirators may not be available? (I know this has not been your observation.) Given our communications, I have decided that pursuing this line of inquiry may not be fruitful for any number of reasons.  I simply can't think my way through the issues you posed at this time. Thank you so much for sharing your vast knowledge with me. It was very generous of you. Best Wishes, Inge

Edward Nardell, MD Moderator Replied at 4:43 PM, 17 Mar 2010

One last comment. That is that as particles, infectious droplet nuclei, are no different than inert particles of a similar size. Using that reasoning, it is easy to compare the protection afforded by various levels of respirators with that provided by surgical masks - essentially fit testing. Admittedly, these are done under optimal conditions, not under working conditions. But at least the major weak link in respiratory protection - face seal leak (not media penetration) can be compared under the same conditions. It then becomes obvious that surgical masks which are not designed to seal around the nose, chin, or sides cannot possibly provide the level of respiratory protection that workers expect when they bother to put on some form of mask/respirator. Is it better than nothing? Probably? Is it adequate? No!!!

To say respirators are not available and that masks must be used instead is similar to accepting taking half doses for TB Rx as OK because full doses are not available. This is totally unacceptable in a world with enough resources - which there are. If you are going to treat TB you must have the drugs. If you are going to protect workers, you need respirators, not surgical masks. Yes, those resources are maldistributed. But any program wishing to do it right can get the resources to do that today - often with some guidance from the outside. Ed

Inge Corless Replied at 4:48 PM, 17 Mar 2010

Dear Ed, I love the combination of science and your passion for providing the right resources. I checked with some colleagues in Uganda and they're using the respirators and appear to be doing so appropriately. I know I saw nurses with surgical masks In India and South Africa and was horrified at the inadequacy of the protection. Given the state of the science, research demonstrating yet again just how inadequate surgical masks are for protecting HCW's seems redundant. The only potential value of such a study is political and that is to promote change. Pro tem, it seems more appropriate to document failures to provide protection than to engage in any bench research. Thank you so much for continuing this discussion. It has been enormously helpful - far more than the literature. All the Best, Inge

Ana Serralheiro Replied at 12:56 AM, 18 Mar 2010

Hi Inge,

Thank you for your contribution. I do understand your concern on the use of the respirators because in Swaziland we face the same problem.
We read and read guidelines saying that the use of respirators in high risk areas is recommended because we are not sure how much environmental measure and administrative alone will protect the HCW in high risk areas.

We also read of recommended isolation when crowded wards without space for cohorting are there. So practically in low-income countries this measures are not feasible!

Going back to the respirators, they are also not there...and then I think about what to tell to the HCW after they read the guidelines? I try to persuade them to focus on the other measures that they can still apply to reduce the risk ... but I actually feel bad sometimes because if I put my self in their position I will be also worried…

Here in Swaziland we do try to implement administrative and environmental measures at the clinics level because of the unreliable supply of respirators. It wouldn't be possible to develop a study that gives better data on the effectiveness of certain environmental measures and administrative measures to avoid transmission to HCW and other hospitalised patients? Meaning in controlled situations with and without respirators?



S. Mehtar Replied at 2:04 AM, 18 Mar 2010

Dear Inge
I have followed the discussion closely and would like to contribute what has been recommended at Tygerberg Hospital which admits approximately 3-10 new TB cases per week! We have noted that transmission occurred when the HCW were not wearing any protection. Where surgical masks were used properly and consistently as part of the PPE, and indeed these are recommended for visitors and patients during transfer, there was no visible increase in transmission. The N95 respirators are used for MDR/XDR-TB, or when HCW are working in close proximity and carrying out risk prone procedures related to the respiratory tract. We fit test a type of N95 and the HCW is responsible for looking after it personally. It may be used for one week. No N95 respirators are left lying around. For prolonged contact ( over 1 hour) we issue expiratory valve N95 for specific HCW duties.
I don't know if this helps but we are still monitoring and keeping an eye. I will let you know if the observation has any more to add.

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Lon)
Chair  IPCAN
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital & Stellenbosch Uni
website: www.ipcanafrica.org
Joint IPCAN/IFIC conference
website: www.ipcan.co.za.
Conference organisers:

S. Mehtar Replied at 2:04 AM, 18 Mar 2010

Sorry, I forgot to say that the patient or source is strongly encouraged to follow the cough etiquette- this does help to reduce dispersal, I think.

Prof Shaheen Mehtar
MBBS, FRC Path (UK), FCPath (Micro) (SA), MD (Lon)
Chair  IPCAN
Head of Academic Unit for Infection Prevention and Control
Tygerberg Hospital & Stellenbosch Uni
website: www.ipcanafrica.org
Joint IPCAN/IFIC conference
website: www.ipcan.co.za.
Conference organisers:

Ana Serralheiro Replied at 2:17 AM, 18 Mar 2010

Dear all,

Thank you prof. Shaheen for your always practical vision.
So in Tygerberg Hospital the visitors are using the surgical mask when they visit the patients in the TB ward?
Regarding the HCW, you're saying that they are presently using it as a protective barrier for TB(non-MDR(XDR TB patients)? And you didn't observe transmission when they are using it? For how long was this observed?



S. Mehtar Replied at 2:28 AM, 18 Mar 2010

Dear Ana
As you know, TB is an occupational disease and the HCW have to report to Occupational Health if they want compensation. The observations have been going on since November, the questionnaire is being revised as we speak. The IPC Team visits the wards regularly and know where the TB patients are so there is also observation. Our main problem is not with our regular trained staff but those that work as locums or additional staff. There are still some mistakes and not wearing PPE but our OH Dept is very strict about it.
It may be early days yet to see how well it works, I will let you know.

Nonkqubela Bantubani Replied at 2:28 AM, 18 Mar 2010

Dear All,

In response to this topic, regarding data on IC practices in health care
facilities, we have done a rapid survey on drug resistant TB in
KwaZulu-Natal and one of our outcome measures was the IC practices. We
do have data that will be presented in Germany in the Lung Health
conference, provided the abstract is accepted. This is a great concern
for a country that has high prevalence of TB and where Nosocomial
transmission has been implicated. As you have mentioned, our country is
resource limited but we have to do our best to focus on the basic IC


Nonkqubela Bantubani

Medical Research Council of SA

Senior Scientist

Clinical and Biomedical TB Research Unit

Moses Bateganya Replied at 4:28 PM, 19 Mar 2010

Dear Proff Shaheen

Your contributions are always very practical. In many other countries on SSA, guidelines are silent on nosocomial TB let alone compensation. The association with HIV also makes HCWs relactant to report. How is this being addressed on your setting. How often are HCWs screened for TB? Where is/should the infoation be obtained? In the personel files or TB clinic?

Moses Bateganya

Sent from my iPhone

S. Mehtar Replied at 3:46 AM, 20 Mar 2010

Dear Moses
We have a quality assurance group made up of IPC, Occ Health and QA. Occ Health manges staff health. TB is an occ disease in SA and all TB in HCW has to be reported, much like NSI. We do not actively screen HCW at all- the reported cases are followed up and evaluated- however currently all get compensation based on the evaluation the risk is graded into high medium and low by IPC and more emphasis on TB-IPC processes is carried out.

Ana Serralheiro Replied at 1:22 AM, 24 Mar 2010

Hi Moses,

In Swaziland we are activelly screening HCW at clinics (primary health centres) and Hospitals throught mobile vans that are part of the "Welness Program". This program was developed as a partnership between the "swaziland nurse Association", the "International Council of Nurses", "The Danish Nurses' Organization", " The Stephen Lewis Foundation", Supported by MoH and BD Corporation.

There's a central Welness Corner in Swaziland where any HCW can go for any health complication.
Since last month their mobile van will start to go every 3 months to all the clinics to do a general check up including screening for TB and offering IPT to those HIV positive. The staff was happy with this because they can test with someone that is not from the facility.

The welness centre will keep a file open per HCW, and it's able to provide data on the number of HCW tested and how many were identified as TB suspects/confimed cases.



S. Mehtar Replied at 2:30 AM, 25 Mar 2010

Hi And
How many have been identified and what support is there for the HCW?

Julia Fischer-Mackey Replied at 9:28 AM, 6 May 2010

Hi All,
You may find this Discussion Brief "Using particulate respirators for TB Infection Control" useful. http://www.ghdonline.org/ic/discussion/how-long-can-n95-masks-be-reused-for-a...

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