face masks: which, when, where and why?

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LEADING ARTICLE Face masks: which, when, where and why? No-one working in hospitals today has known a time when face masks have not been worn in the operating theatres as well as on the wards. All the masks that are now used are disposable. In the operating theatre, surgeons, assisting nurses and anacsthctists should wear masks, although they are frequently misused, either because they are not made to cover the nose or by the mask being removed from over the mouth and nose and then later replaced in its correct position, a manoeuvre which can contaminate the hands and the outside of the mask. ‘I’wenty years ago Hare (1962) put forward strong arguments against the use of face masks on the wards, where they are now worn for fewer procedures than they were when Hare made his plea. Recently in this Journal (Taylor, 1980) an answer to the question ‘Are face masks necessary in operating theatres and wards?’ repeated many of Hare’s arguments and summed up the arguments and reports which show how little risk there is if masks are not worn in the wards. The earlier masks were made of several layers of gauze or linen (Paine, 1935; Shooter, Smith & Hunter,, 1959) and were r-e-used after they had been sterilized. The masks were improved when a piece of paper or cellophane was inserted between the linen layers to provide an impervious barrier. In the last 2.5 years all the earlier masks have been replaced by disposable theatre masks made out of synthetic fibres, which allow the wearer to breathe in and out through the mask: several of these contain fibreglass mats which provide very efficient filters, but the fibreglass has caused an eruption on some users’ faces so many manufacturers provide alternative masks with filters made of polyester (Bard Vigilon, Deseret- no glass, White Knight-no glass) or polypropylene (3M 181X and Filtron). Whilst the newer disposable theatrc masks were being introduced, much cheaper disposable paper masks were made for use in the wards. The question as to when these should be worn is a vexed one. Although this is controversial, the author recommends the use of masks to protect the patient in the following situations: when performing lumbar punctures, when dissecting out a vein for intravenous therapy or inserting a central venous or arterial catheter as well as when dressing large open wounds, and to protect the staff when sucking out a patient’s trachea so that the operators do not have droplets propelled into their faces when the patient coughs. The observers in a theatre, that is those who are not going near the patient, could wear the cheaper paper mask. These masks should probably be worn if alimentation formulae are not made in the diet kitchen. The efficiency of masks has been tested when the masks have been worn normally and then challenged by words spoken softly or loudly, or by expelling air in a uniform manner: they have been stretched across a funnel and challenged in several ways by expelled air- (Thomas, 1961; Rogers, 1980). The masks have also been mounted on a plaster cast of a face (Paine, 1935), on a carefully made manikin head with a hard nose and soft cheeks (Madsen & Madsen, 1967) or stretched between metal flanges (Rubbo & Abbott, 1968). The masks placed in these orps-6701/81/orooor + 04 $or.oo/o 0 1981 Academic Press Inc. (London) Limited 1

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LEADING ARTICLE

Face masks: which, when, where and why?

No-one working in hospitals today has known a time when face masks have not been worn in the operating theatres as well as on the wards. All the masks that are now used are disposable. In the operating theatre, surgeons, assisting nurses and anacsthctists should wear masks, although they are frequently misused, either because they are not made to cover the nose or by the mask being removed from over the mouth and nose and then later replaced in its correct position, a manoeuvre which can contaminate the hands and the outside of the mask.

‘I’wenty years ago Hare (1962) put forward strong arguments against the use of face masks on the wards, where they are now worn for fewer procedures than they were when Hare made his plea. Recently in this Journal (Taylor, 1980) an answer to the question ‘Are face masks necessary in operating theatres and wards?’ repeated many of Hare’s arguments and summed up the arguments and reports which show how little risk there is if masks are not worn in the wards.

The earlier masks were made of several layers of gauze or linen (Paine, 1935; Shooter, Smith & Hunter,, 1959) and were r-e-used after they had been sterilized. The masks were improved when a piece of paper or cellophane was inserted between the linen layers to provide an impervious barrier. In the last 2.5 years all the earlier masks have been replaced by disposable theatre masks made out of synthetic fibres, which allow the wearer to breathe in and out through the mask: several of these contain fibreglass mats which provide very efficient filters, but the fibreglass has caused an eruption on some users’ faces so many manufacturers provide alternative masks with filters made of polyester (Bard Vigilon, Deseret- no glass, White Knight-no glass) or polypropylene (3M 181X and Filtron).

Whilst the newer disposable theatrc masks were being introduced, much cheaper disposable paper masks were made for use in the wards. The question as to when these should be worn is a vexed one. Although this is controversial, the author recommends the use of masks to protect the patient in the following situations: when performing lumbar punctures, when dissecting out a vein for intravenous therapy or inserting a central venous or arterial catheter as well as when dressing large open wounds, and to protect the staff when sucking out a patient’s trachea so that the operators do not have droplets propelled into their faces when the patient coughs. The observers in a theatre, that is those who are not going near the patient, could wear the cheaper paper mask. These masks should probably be worn if alimentation formulae are not made in the diet kitchen.

The efficiency of masks has been tested when the masks have been worn normally and then challenged by words spoken softly or loudly, or by expelling air in a uniform manner: they have been stretched across a funnel and challenged in several ways by expelled air- (Thomas, 1961; Rogers, 1980). The masks have also been mounted on a plaster cast of a face (Paine, 1935), on a carefully made manikin head with a hard nose and soft cheeks (Madsen & Madsen, 1967) or stretched between metal flanges (Rubbo & Abbott, 1968). The masks placed in these

orps-6701/81/orooor + 04 $or.oo/o 0 1981 Academic Press Inc. (London) Limited

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2 K. B. Rogers

positions have been challenged for their ability to prevent a fine aerosol containing organisms passing through them. The organisms have often been selected because of some cultural characteristic which makes their identification easy: Mimococcus Zysodeikticus (Paine, 1935), Bacillus stearothermophilus (Madsen & Madsen, 1967), Serratia marcescens (Thomas 1961; Ford & Peterson 1963; Ford, Peterson & Mitchell, 1967), a T2 Escherichia coli bacteriophage (Nicholes, 1964), a penicillin- resistant Staphylococcus aureus (Dineen, 1971) and Staphylococcus epidermidis (Rubbo & Abbott, 1968). The organisms passing through the masks have been collected by three principal methods. In England by the Bourdillon slit sampler (Bourdillon, Lidwell & Thomas, 1941) and in America by the Andersen Cascade sampler (Andersen, 1958) as well as by settle plates (Shooter et al., 1959; Thomas, 1961). Those who have used the Andersen sampler and challenged the masks with aerosols containing bacteria, have usually mounted the mask across the entry to the sampler (Ford &Peterson, 1963 ; Nicholes, 1964; Ford, Peterson & Mitchell, 1967; Dineen, 1971; Sommers, 1973). Shooter et al. (1959) isolated the heads of seated volunteers in a chamber supplied with filtered air and the organisms were collected on settle plates and in a Bourdillon slit sampler. This technique showed that organisms could be deflected at the sides and back of the mask, which other workers have not usually demonstrated. Greene & Vesley (1962) also had volunteers’ heads isolated in a chamber, but their volunteers were standing: they did not use settIe plates and the organisms were collected by an Andersen sampler.

Those who have made their tests when using natural emissions of normal nasopharyngeal flora, have found that care must be taken to eliminate the ambient airborne contaminants (Greene Sz: Vesley, 1962). Rogers (1980) eliminated these by making his tests in a laboratory safety cabinet, so that the masks were only challenged by the organism laden particles produced for each challenge. His techniques could not demonstrate how many organisms escaped from the sides of the masks, as would have been possible in Shooter’s method and as the paper mask (Promask) he recommended allows no organism laden particles to pass forward, it is probable that many escape backwards from the back of th.e mask. However, in a ward, the general activity of staff moving, the patients and staff talking, and with perhaps some patients coughing, the organisms escaping behind the wearer of a Promask during ordinary speaking would not add seriously to the risk of the patient.

Although he only used his own expulsions of air to produce his loudly spoken tuts or raspberries, Rogers (1980) was unable to provide either uniform challenges of the masks or of control expulsions of air when no masks were worn. He quoted findings of other workers who had a similar variation in their challenges: this is not so unexpected when individuals make repeated challenges, but it is when the tests were made with standardized aerosols of nebulised bacterial suspensions.

Even more surprising than this variation in the counts that most workers have obtained, is the different efficiencies that have been reported on the same masks. Dineen (1971) calculated that the Aseptex mask was 36.8 per cent efficient, the Deseret EZ breathe 91.1 per cent and the Surgine mask 94 per cent efficient. Quesnel(l975) f ound the same three masks’ efficiencies to be 94, 98.8 and 95.8 per

Face masks 3

cent, whereas Rogers (1980) h s owed they were 60.7, 99.2, and 99.4 per cent efficient. Rubbo & Abbott (1968) only tested two of these masks and found the Aseptex to be 40.0 and the Deseret 99 per cent efficient: the same two masks were amongst those tested by Ford, Peterson & Mitchell (1967) who showed efficiencies of 39.6 and 99.7 per cent. The fact that some masks prove uniformally good is understandable, but it is difficult to explain a variation between 36.8 and 98.4 per cent efficiency for the same mask, unless the challenges were not sufficiently searching and stringent in the experiments which apparently showed that the mask was highly efficient. Some workers might claim that masks need not be subjected to tests th.at are too severe, but the use of stringent tests on masks is analogous to a bacteriological method used to check any autoclave, when non- pathogenic spores have to be killed by the autoclave even though it is hoped no pathogenic spores will be on articles placed in the autoclave.

Extra tests without a mask, controls, are usually performed to show how many bacteria laden particles would be grown if no masks were worn and a mask’s percentage efficiency is calculated from these control counts. In Rubbo & Abbott’s (1968) cleverly designed apparatus the tests and the controls were made simultaneously, with the conditions of each identical as regards the rate of air flow, its volume, humidity and concentration of bacterial aerosol. Because of the scatter of the results of the test and control experiments of other workers it would have been valuable if Rubbo and Abbott had published the actual counts from which they calculated the percentage efficiency of their masks, particularly as most of them were only tested twice.

The bacteriological efficiency of apparatus and materials employed by hospitals is sometimes not questioned: makers often modify an article, usually to improve it but sometimes, without notifying the users, only to reduce the cost of production, and these modifications may diminish the efficiency of the article. There is a danger that a hospital’s supplies officer will purchase a product because it is relatively cheap: such an article could be inefficient which may only be discovered when an untoward incident results from its use. The hospital microbiologist is rarely consulted over the choice of face masks: should he be involved with their selection he is well advised to limit his advice to that concerned with the mask’s efficiency and comfort. The makers may give him a recommended price (RP), which they also give to their distributors, but a good hospital supplies officer will negotiate a much lower price from the distributor than the makers’ RP.

The makers’ RPs of theatre masks vary from 4.96~ to 8.9~ each, and some makers’ masks with fibreglass filters are cheaper than those they make without fibreglass. The paper masks vary between 0.73~ and 1.94~ each and the Promask which Rogers (1980) recommended is not the most expensive of these.

The recently published Code of Practice (1978) makes no reference to the use of face masks in either clinical laboratories or postmortem rooms, but states that to prevent conjunctival contamination visors must be worn to provide full face protection for the postmortems on certain special risk cases, which were defined as those who have died from viral hepatitis, brucellosis or leptospirosis. The report states that during the post-mortem examinations of certain ‘risk cases’, amongst

4 K. B. Rogers

which are known suspected cases of tuberculosis, the visors will be worn. But these would not protect the P.M. room’s personnel from the inhalation of the bacteria laden droplets, produced when the lungs are cut to obtain material for bacterio- logical cultures. During such post-mortems the staff should wear a good theatre- type mask: Rogers (1980) showed there are many of these available on the English market, such as the Bard Vigilon, the Deseret EZ breathe, the 3M 1818, Seward’s no glass, Johnson & Johnson’s Surgine and White Knight Standard.

K. B. Rogers Northwick Park Hospital

References

Andersen, A. A. New sampler for the collection, sizing and enumeration of viable airborne particles. Journal of Bacteriology 76: 471-84 (1958).

Bourdillon, R. B., Lidwell, 0. M. & Thomas, J. C. A split sampler for collecting and counting airborne bacteria. Journal of Hygiene (Cambridge) 41: 197-224 (1941).

DHSS. Code of Practice for the Prevention of Infection in Clinical Laboratories and Post- mortem Rooms. HMSO, London (1978), pp. 39 & 41.

Dineen, P. Microbial filtration by surgical masks. Surgery, Gynecology and Obstetrics 133: 812-14 (1971).

Ford, C. R. & Peterson, D. E. The efficiency of surgical face masks. American Journal of Swgery 106: 954-57 (1963).

Ford, C. R., Peterson, D. E. & Mitchell, C. R. An appraisal of the role of surgical face masks. American Journal of Surgery 113: 787-90 (1967).

Greene, V. W. & Vesley, D. Methods for evaluating effectiveness of surgical masks. Journal of Bacteriology 83: 663-66 (1962).

Hare, R. To mask or not to mask? Nursing Times 59: 715 (1962). Madsen, P. 0. & Madsen, R. E. A study of disposable surgical masks. American Journal of

Surgery 114: 432-35 (1967). Nicholes, P. S. Comparative evaluation of a new surgical mask medium. Surgery, Gynecology

and Obstetrics 118: 579-83 (1964). Paine, C. G. The aetiology of puerperal infection with special reference to droplet infection.

Lancet i: 243-46 (1935). Quesnel, L. B. The efficiency of surgical masks of varying design and composition. British

Journal of Surgery 62: 936-40 (1975). Rogers, K. B. An investigation into the efficiency of disposable face masks. Journal of

Clinical Pathology, 33: 1086-1091 (1980). Rubbo, S. D. & Abbott, L. R. Filtration efficiency of surgical masks: a new method of

evaluation. Australia and New Zealand Journal of Surgery 38: 80-83 (1968). Shooter, R. A., Smith, M. A. & Hunter, C. J. W. A study of surgical masks. BritishTournaZ

of Surgery 47: 246649 (1959). Sommers, J. R. Surgical face masks. Bacterial filtration efficiencies study. Surgikos 55:

481-82 (1978). Taylor, L. Questions and answers. ‘Are face masks necessary in operating theatres and

wards?’ If so what type do you recommend? Journal of Hospital Infection 1: 173-74 (1980).

Thomas, C. G. A. Efficiency of surgical masks in use in hospital wards. Guy’s Hospital Reports 110: 157-167 (1961).