Bacterial contamination of forehead skin and surgical mask in aerosol-producing dental treatment

Figures & data

Figure 1.  Sampling using an eSwab™. The entire forehead area not covered by hair was wiped off for 5–8 s

Figure 2.  (a) Surgical mask with the area to be pressed onto agar indicated by the blue ellipse. (b) Surgical mask being pressed onto the agar surface

Table 1. Quantitative analysis of bacterial contamination on forehead skin and surgical masks

Samples (n = 67)	Positive	%	Bacterial score (median)
Forehead before treatment	63	94	2
Forehead after treatment	64	95.5	2
Surgical mask after treatment	53	79	1

No statistically significant differences between positive samples and bacterial scores for the forehead skin before and after treatment; Wilcoxon signed-rank test, p < 0.05

Quantitative analysis. Samples of surgical masks and forehead skin with bacterial growth on agar plates in absolute numbers and percentages. Median bacterial scores: 0 = no bacterial growth; 1 = ≤10² colonies; 2 = >10² colonies; and 3 = dense bacterial growth.

Table 2. Bacterial species detected in forehead skin swabs and surgical mask samples from dental professionals exposed to treatment-related aerosols and droplets

Microbial species	Resident skin microbiota	Facultative or obligate oral microbiota	Typical habitat	Forehead before exposure	Forehead after exposure	Surgical mask
Acinetobacter lwoffi	+	f	skin, oropharynx, perineum	1	1	1
A. ursingii	+	−	skin, oropharynx, perineum	2	0	0
Bacillus spp.	−	−	ubiquitous, environment, soil	3	1	2
B. cereus	−	−	ubiquitous, environment, soil	1	4	5
B. flexus	−	−	poultry manure, environment	0	0	1
B. pumilus	−	−	ubiquitous, environment, soil	2	1	0
B. subtilis	−	−	ubiquitous, environment, soil, water	0	0	1
Clostridium spp.	−	−	ubiquitous, digestive tract	0	0	1
Corynebacterium spp.	+	f	skin, mucous membranes	0	0	1
Escherichia coli	−	−	gut, feces	0	0	1
Kocuria spp.	−	−	soil	1	0	0
K. rhizophila	−	−	soil	2	2	0
Leclercia adecarboxylata	−	−	colon of warm-blooded animals	0	0	1
Lactococcus lactis	−	−	production of cheese, kefir, and soured milk	1	0	0
Micrococcus spp.	+	−	ubiquitous, skin, environment	0	0	1
M. luteus	+	−	air, meat and dairy products, skin	3	1	8
Neisseria subflava	−	o	upper airways	1	0	0
Propionibacterium spp.	+	−	skin, urogenital tract, gut	4	3	0
P. acnes	+	−	skin	5	2	0
Pseudomonas stutzeri	−	−	soil	2	0	0
Rothia dentocariosa	−	o	oral cavity	0	0	5
Staphylococcus aureus (MSSA)	+	f	skin, mucous membranes	3	3	4
S. auricularis	+	f	skin, oral cavity	1	0	0
S. capitis	+	f	skin, mucous membranes	27	28	15
S. coagulase negative	+	f	skin, mucous membranes, oral cavity	1	0	1
S. epidermidis	+	f	skin, mucous membranes	50	52	33
S. haemolyticus	+	−	skin (axilla), mucous membranes	0	0	1
S. hominis	+	f	skin, mucous membranes	4	1	3
S. pettenkoferi	+	−	skin, blood cultures	1	0	0
S. saprophyticus	−	−	urinary tract, vagina, rectum, beef and pork products	5	6	5
S. schleiferi	+	−	skin	0	0	1
S. warneri	+	−	skin	1	0	1
Streptococcus spp.	−	o	oral cavity, digestive tract, urogenital tract	0	1	0
S. alpha hemolytic	−	o	oral cavity, digestive tract, urogenital tract	0	1	2
S. constellatus	−	o	oral cavity, digestive tract, urogenital tract	0	0	2
S. infantis	−	o	oral cavity, throat, nasopharynx	0	0	1
S. mitis	−	o	oral cavity, throat, nasopharynx	2	0	3
S. oralis	−	o	oral cavity biofilms	0	1	2
S. parasanguinis	−	o	oral cavity biofilms	0	0	2
Gram-positive viridans streptococci	−	o	oral cavity biofilms, caries, upper airways, nose	1	0	0

Qualitative analysis. Bacterial species in alphabetical order detected on the forehead´s skin and masks of dental professionals. The second and third columns indicate whether the species is classified as part of the resident skin microbiota (+/−) and as facultative (f) or obligate (o) oral bacteria. The numbers indicate the detection frequencies of the species on forehead skin before and after performing treatment and on surgical masks (max. n = 67 each). Colonies identified on the upper taxonomic levels are indicated as spp. or as Gram-positive or Gram-negative rods, coagulase-negative staphylococci, or alpha hemolytic streptococci.

Table 3. Samples from surgical masks and forehead swabs found to contain obligate or facultative oral bacteria

	(I) Obligate oral bacteria	(II) Facultative oral species detected on the forehead skin and surgical mask after treatment but not before treatment	(III) Facultative oral species on the forehead skin or surgical mask after treatment but not before treatment	(IV) Facultative oral species detected on the forehead skin before and after treatment with increases in bacterial scores
Number of samples	67	67	61, II excluded	61, II excluded
Forehead before treatment	2 (3%)	–	–	17 (28%)^d
Forehead after treatment	4 (6%)	6 (9%)	13 (21%)^b
Surgical mask	17 (25%)^a		16 (26%)^c	–

^asignificant difference from forehead skin after treatment, p = 0.001

^bsignificant difference from forehead skin after treatment, p = 0.001

^csignificant difference from forehead skin after treatment, p = 0.0004

^dsignificant difference from forehead skin after treatment, p = 0.005, Wilcoxon signed-rank test, p < 0.05

Samples from surgical masks and forehead swabs found to contain obligate or facultative oral bacteria. Data are displayed as numbers, percentages (in parentheses), and maximum numbers of samples.