British Journal of Anaesthesia 1992; 69: 407-408
SURGICAL FACE MASKS ARE EFFECTIVE IN REDUCING BACTERIAL CONTAMINATION CAUSED BY DISPERSAL FROM THE UPPER AIRWAY B. J. PHILIPS, S. FERGUSSON, P. ARMSTRONG, F. M. ANDERSON AND J. A. W. WILDSMITH
SUMMARY
KEY WORDS Anaesthetic techniques: regional. Complications: bacterial contamination. Equipment • surgical face mask.
A serious complication of subarachnoid block is bacterial meningitis, and a meticulous aseptic technique is vital, although one component of that, the wearing of a surgical face mask, has been questioned recently [1]. In this study, we examined the effect of wearing a face mask on bacterial contamination under conditions similar to those found during spinal anaesthesia. METHOD AND RESULTS
Twenty-five anaesthetists (ages 25-45 yr) volunteered to take part in the study. Each sat on a chair in a draught-free room and a blood agar plate was positioned flat against the wall 30 cm away from the subject's mouth. The subject spoke directly at the agar plate for 5 min. A fresh, standard, soft, pleated, non-glass fibre face mask (Brevet) was then worn and the subject continued to speak for a further 15 min (three 5-min intervals). Further blood agar plates were positioned in front of the subject's mouth during the first and third 5-min periods. The agar dishes were sealed and taken immediately to the Department of Clinical Bacteriology-where they were incubated for 24 h at 37 °C in a carbon dioxide-rich environment. The bacterial colonies that grew were counted and identified using standard laboratory techniques. The results were analysed using ANOVA, followed by a two-sample Student's t test.
Io 4
A
B
C
FIG. 1. Number of colonies grown in the agar plates in group A (no face mask), group B (face mask 0-5 min) and group C (face mask 10-15 min): mean number of colonies grown (horizontal bars) and 95 % confidence limits (vertical bars). B.J.PHILIPS, M.B., B.S.; P.ARMSTRONG, F.R.C.ANAES.; J. A. W. WILDSMITH, M.D., F.R.C.ANAES.; Department of Anaesthetics,
Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh EH3 9YW. S. FERGUSSON, F.I.M.L.S.; F.M.ANDERSON, M.R.C.PATH.;
Department of Medical Microbiology, Medical School, Teviot Place, Edinburgh EH8 9AG. Accepted for Publication: April 23, 1992.
Downloaded from http://bja.oxfordjournals.org/ at Université Laval on July 3, 2015
We have studied the effectiveness of surgical face masks in reducing bacterial contamination of a surface, produced by dispersal of organisms from the upper airway. Twenty-five volunteers were asked to speak at blood agar plates positioned in close proximity to the mouth, initially whilst not wearing a face mask and then wearing a surgical face mask over the mouth and nose. A fresh face mask almost completely abolished bacterial contamination of agar plates 30 cm from the mouth. After 15 min there was an increase in the level of contamination which was statistically insignificant.
At least one colony grew on 13 of the 25 plates collected from unmasked subjects (mean numbers of colonies 3.6, range 0-24), whereas only three plates were found to be contaminated, with only one colony on each, when a fresh face mask was worn (fig. 1). After the face mask had been worn for 10 min, nine plates were contaminated (mean number of colonies 1, range 0-10). In this last set, only one plate grew as many as 10 colonies, the remaining eight producing between one and three colonies. The contamination of the plate was less when the subject was wearing a face mask, both fresh and worn for 10 min, than when they were unmasked. These differences were statistically significant (P < 0.01 fresh face mask; P < 0.05 worn face mask). There was no statistical difference between the numbers of colonies grown on the plates obtained at the two intervals when the masks were worn.
BRITISH JOURNAL OF ANAESTHESIA
408
All the bacteria grown were normal upper respiratory commensals: coagulase negative Staphylococd, alpha-haemolytic Streptococci, Micrococci, Moraxella catarrhalis and a coliform (one colony).
COMMENT
REFERENCES 1. Yentis SM. Wearing of face masks for spinal anaesthesia. British Journal of Anaesthesia 1992; 68: 224. 2. Lee JJ, Parry H. Bacterial meningitis following spinal anaesthesia for Caesarean section. British Journal of Anaesthesia 1991; 66: 383-386. 3. Berga S, Trierweiler MW. Bacterial meningitis following epidural anesthesia for vaginal delivery: a case report. Obstetrics and Gynecology 1989; 74: 437-438. 4. Ayliffe GAJ. Masks in surgery ? Journal of Hospital Infection 1991; 18: 165-166. 5. Rirter MA, Eitzen H, French MLV, Han J. The operating room environment as affected by people and the surgical face mask. Clinical Orthopaedics and Related Research 1975; 111: 147-150. 6. Dineen P. Microbial filtration by surgical masks. Surgery, Gynecology & Obstetrics 1971; 133: 812-814.
Downloaded from http://bja.oxfordjournals.org/ at Université Laval on July 3, 2015
The results indicate that wearing a face mask produced a marked reduction in the bacterial contamination of a surface in close proximity to the upper airway. Bacterial colonies grew on more than 50% of the plates obtained while the subject was not wearing a face mask. A fresh face mask almost abolished contamination, and after 15 min wear there was only a small and insignificant increase in the number of organisms isolated. Subarachnoid blocks are performed by a large number of anaesthetists who vary in both their technique and their experience. Similarly, the blocks vary in their degree of difficulty, from being quick and easy to being time-consuming and difficult to perform. In our study, we aimed to simulate conditions which would represent those occurring in the majority of cases in which subarachnoid blocks are sited. The agar dishes were placed at a distance and height judged to be similar to that between mouth and operating field and the area of the agar dish was similar to the opening in a sterile drape. The time intervals were chosen as being representative of how long it may take to perform a subarachnoid block. The organisms grown were normal upper respiratory commensals. These are of low pathogenicity and virulence and are unlikely to cause infection in the wound of a patient with an intact immune system. However, the central nervous system has no such defences when its coverings are breached, and cerebrospinal fluid provides bacteria with an ideal culture medium. Bacterial meningitis is rare after subarachnoid block, but occasional reports continue to appear, usually with the source of infection unclear [2]. The diagnosis of bacterial meningitis as opposed to aseptic meningitis is often made from the CSF biochemistry rather than from positive cultures. Even so, there are reports of meningitis produced by organisms normally of low pathogenicity, such as Streptococcus sanguis—an alpha-haemolytic streptococcus associated usually with dental caries [3]. In that case, the probable source of infection was a blood patch performed for headache caused by accidental dural puncture, although it does illustrate
that usually benign organisms may cause CSF infection. Furthermore, clinicians may carry more virulent pathogens, and we have shown that working surfaces could become contaminated with airway flora. In a recent review, Ayliffe [4] concluded that it was probably unnecessary to wear a face mask in theatre to reduce wound infections, although he did state that there was little evidence to support this. Ritter and colleagues [5] found that the wearing of face masks made no difference to the contamination of agar dishes 1.20 m above the floor within a theatre suite. This was probably because the effect of people merely being present was so great. A similar argument could be applied to ward work, where large numbers of people are moving about and causing considerable contamination from other sources. During subarachnoid blocks, masks are likely to be far more important because the operator's airway is in such close proximity to the field of work. In our study, no attempt was made to reduce surrounding contamination, the volunteers did not wear theatre clothing and others were not excluded from the room. Nevertheless, the use of a fresh face mask virtually abolished contamination of the agar plates. The type of mask is important. Simple paper or cloth masks provide little benefit; the most effective are large, soft, pleated and pliable masks, the actual material being unimportant [6]. The better ones, when tested in vitro, remained good bacterial filters for 8 h, but we found a small increase in agar plate contamination after the face mask had been worn for 15 min. Although the increase was statistically insignificant, it may be advisable to wear a fresh face mask for each procedure.
SURGICAL FACE MASKS ARE EFFECTIVE IN REDUCING BACTERIAL CONTAMINATION CAUSED BY DISPERSAL FROM THE UPPER AIRWAY B. J. PHILIPS, S. FERGUSSON, P. ARMSTRONG, F. M. ANDERSON AND J. A. W. WILDSMITH
SUMMARY
KEY WORDS Anaesthetic techniques: regional. Complications: bacterial contamination. Equipment • surgical face mask.
A serious complication of subarachnoid block is bacterial meningitis, and a meticulous aseptic technique is vital, although one component of that, the wearing of a surgical face mask, has been questioned recently [1]. In this study, we examined the effect of wearing a face mask on bacterial contamination under conditions similar to those found during spinal anaesthesia. METHOD AND RESULTS
Twenty-five anaesthetists (ages 25-45 yr) volunteered to take part in the study. Each sat on a chair in a draught-free room and a blood agar plate was positioned flat against the wall 30 cm away from the subject's mouth. The subject spoke directly at the agar plate for 5 min. A fresh, standard, soft, pleated, non-glass fibre face mask (Brevet) was then worn and the subject continued to speak for a further 15 min (three 5-min intervals). Further blood agar plates were positioned in front of the subject's mouth during the first and third 5-min periods. The agar dishes were sealed and taken immediately to the Department of Clinical Bacteriology-where they were incubated for 24 h at 37 °C in a carbon dioxide-rich environment. The bacterial colonies that grew were counted and identified using standard laboratory techniques. The results were analysed using ANOVA, followed by a two-sample Student's t test.
Io 4
A
B
C
FIG. 1. Number of colonies grown in the agar plates in group A (no face mask), group B (face mask 0-5 min) and group C (face mask 10-15 min): mean number of colonies grown (horizontal bars) and 95 % confidence limits (vertical bars). B.J.PHILIPS, M.B., B.S.; P.ARMSTRONG, F.R.C.ANAES.; J. A. W. WILDSMITH, M.D., F.R.C.ANAES.; Department of Anaesthetics,
Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh EH3 9YW. S. FERGUSSON, F.I.M.L.S.; F.M.ANDERSON, M.R.C.PATH.;
Department of Medical Microbiology, Medical School, Teviot Place, Edinburgh EH8 9AG. Accepted for Publication: April 23, 1992.
Downloaded from http://bja.oxfordjournals.org/ at Université Laval on July 3, 2015
We have studied the effectiveness of surgical face masks in reducing bacterial contamination of a surface, produced by dispersal of organisms from the upper airway. Twenty-five volunteers were asked to speak at blood agar plates positioned in close proximity to the mouth, initially whilst not wearing a face mask and then wearing a surgical face mask over the mouth and nose. A fresh face mask almost completely abolished bacterial contamination of agar plates 30 cm from the mouth. After 15 min there was an increase in the level of contamination which was statistically insignificant.
At least one colony grew on 13 of the 25 plates collected from unmasked subjects (mean numbers of colonies 3.6, range 0-24), whereas only three plates were found to be contaminated, with only one colony on each, when a fresh face mask was worn (fig. 1). After the face mask had been worn for 10 min, nine plates were contaminated (mean number of colonies 1, range 0-10). In this last set, only one plate grew as many as 10 colonies, the remaining eight producing between one and three colonies. The contamination of the plate was less when the subject was wearing a face mask, both fresh and worn for 10 min, than when they were unmasked. These differences were statistically significant (P < 0.01 fresh face mask; P < 0.05 worn face mask). There was no statistical difference between the numbers of colonies grown on the plates obtained at the two intervals when the masks were worn.
BRITISH JOURNAL OF ANAESTHESIA
408
All the bacteria grown were normal upper respiratory commensals: coagulase negative Staphylococd, alpha-haemolytic Streptococci, Micrococci, Moraxella catarrhalis and a coliform (one colony).
COMMENT
REFERENCES 1. Yentis SM. Wearing of face masks for spinal anaesthesia. British Journal of Anaesthesia 1992; 68: 224. 2. Lee JJ, Parry H. Bacterial meningitis following spinal anaesthesia for Caesarean section. British Journal of Anaesthesia 1991; 66: 383-386. 3. Berga S, Trierweiler MW. Bacterial meningitis following epidural anesthesia for vaginal delivery: a case report. Obstetrics and Gynecology 1989; 74: 437-438. 4. Ayliffe GAJ. Masks in surgery ? Journal of Hospital Infection 1991; 18: 165-166. 5. Rirter MA, Eitzen H, French MLV, Han J. The operating room environment as affected by people and the surgical face mask. Clinical Orthopaedics and Related Research 1975; 111: 147-150. 6. Dineen P. Microbial filtration by surgical masks. Surgery, Gynecology & Obstetrics 1971; 133: 812-814.
Downloaded from http://bja.oxfordjournals.org/ at Université Laval on July 3, 2015
The results indicate that wearing a face mask produced a marked reduction in the bacterial contamination of a surface in close proximity to the upper airway. Bacterial colonies grew on more than 50% of the plates obtained while the subject was not wearing a face mask. A fresh face mask almost abolished contamination, and after 15 min wear there was only a small and insignificant increase in the number of organisms isolated. Subarachnoid blocks are performed by a large number of anaesthetists who vary in both their technique and their experience. Similarly, the blocks vary in their degree of difficulty, from being quick and easy to being time-consuming and difficult to perform. In our study, we aimed to simulate conditions which would represent those occurring in the majority of cases in which subarachnoid blocks are sited. The agar dishes were placed at a distance and height judged to be similar to that between mouth and operating field and the area of the agar dish was similar to the opening in a sterile drape. The time intervals were chosen as being representative of how long it may take to perform a subarachnoid block. The organisms grown were normal upper respiratory commensals. These are of low pathogenicity and virulence and are unlikely to cause infection in the wound of a patient with an intact immune system. However, the central nervous system has no such defences when its coverings are breached, and cerebrospinal fluid provides bacteria with an ideal culture medium. Bacterial meningitis is rare after subarachnoid block, but occasional reports continue to appear, usually with the source of infection unclear [2]. The diagnosis of bacterial meningitis as opposed to aseptic meningitis is often made from the CSF biochemistry rather than from positive cultures. Even so, there are reports of meningitis produced by organisms normally of low pathogenicity, such as Streptococcus sanguis—an alpha-haemolytic streptococcus associated usually with dental caries [3]. In that case, the probable source of infection was a blood patch performed for headache caused by accidental dural puncture, although it does illustrate
that usually benign organisms may cause CSF infection. Furthermore, clinicians may carry more virulent pathogens, and we have shown that working surfaces could become contaminated with airway flora. In a recent review, Ayliffe [4] concluded that it was probably unnecessary to wear a face mask in theatre to reduce wound infections, although he did state that there was little evidence to support this. Ritter and colleagues [5] found that the wearing of face masks made no difference to the contamination of agar dishes 1.20 m above the floor within a theatre suite. This was probably because the effect of people merely being present was so great. A similar argument could be applied to ward work, where large numbers of people are moving about and causing considerable contamination from other sources. During subarachnoid blocks, masks are likely to be far more important because the operator's airway is in such close proximity to the field of work. In our study, no attempt was made to reduce surrounding contamination, the volunteers did not wear theatre clothing and others were not excluded from the room. Nevertheless, the use of a fresh face mask virtually abolished contamination of the agar plates. The type of mask is important. Simple paper or cloth masks provide little benefit; the most effective are large, soft, pleated and pliable masks, the actual material being unimportant [6]. The better ones, when tested in vitro, remained good bacterial filters for 8 h, but we found a small increase in agar plate contamination after the face mask had been worn for 15 min. Although the increase was statistically insignificant, it may be advisable to wear a fresh face mask for each procedure.
