Journal of Hospital Infection (1985) 6 (Supplement), 51-57

N e w methods for determining pre-operative and postoperative skin disinfection

K. O. G u n d e r m a n n , B/irbel C h r i s t i a n s e n and Chr i s t iane H611er

Abteilung Hygiene, Sozial und Gesundheitswesen, Zentrum Klinisch- Theoretische Medizin 1 im Klinikum der Universitdt Kiel, Brunswiker Str. 2-6,

2300 Kiel 1, F R G

Summary: A comparison was made of the Thran pressurized spray gun and scrubbing with cotton swabs on the removal of organisms from the skin. Both methods showed similar results but sometimes considerable differences in counts were found on adjacent skin areas. The cotton swab method was used to compare the effect of 60 or 70% isopropanol and 10% povidone- iodine on the flora of the outer side of the upper arm over 24 h. With the exception of one test person, no significant difference was found between the disinfectants.

Introduction

T h e r e is, as yet, no general ly accepted test for p re -opera t ive and pos topera t ive skin dis infect ion of the opera t ion site. In G e r m a n y the effectiveness of ' hyg ien i c ' hand dis infect ion has been assessed by the D G H M (1981) m e thod . | t y g i e n i c hand disinfect ion, the aim of which is to cause a large r educ t ion in the t rans ient flora, m u s t be quick bu t need have no con t inu ing action. In dis infect ion of the ope ra t i on site, however , the a im is to reduce the n u m b e r s of the resident as well as the t rans ien t flora and to obta in a con t inu ing act ion for some t ime after the opera t ion, p r even t ing the emergence on the surface of bacter ia f rom the deeper layers of the skin.

Hyg ien ic hand dis infect ion is assessed by app ly ing a suspens ion of Escherichia coli and then t reat ing the skin with an antiseptic, the aim be ing to cause a reduc t ion of at least 3 log in the coun t s of E. coli f rom the skin, c o m p a r e d with p r e - t r e a t m e n t levels. I t is ques t ionable whe the r one needs to achieve such a large r educ t ion in the res ident flora on dis infect ion of the opera t ion site.

T h e r e has not been m u c h s tudy on m e t h o d s used for assessing surgical dis infect ion of the hands on d is infec t ion with p repara t ions used for the opera t ion site. Dis in fec t ion of the skin of the opera t ion site needs t r e a t m e n t with the ant isept ic for at least 5 min.

T h i s s tudy was unde r t aken because of the need for a quant i ta t ive test of the act ion of ant isept ics against the res ident flora at the opera t ion site,

0195 6701185/06A1151 +07 $02.00/0

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((~) 1985 The flospital Infectiun Society

52 K. O. G u n d e r m a n n e t aL

including assessment of continuing action of antiseptics applied to the skin for longer periods.

Measurement of the effects on the resident flora of treating the skin with an antiseptic must give adequately reproducible results. T h e methods that have been tried involve contact transfer, rinsing and swabbing. Contact transfer methods show poor reproducibility, possibly due to differences between persons in the greasiness (or amount of sebaceous secretion) of the skin. The two other types of sampling method appeared more promising, and were used in our preliminary study; we rejected methods that caused irritation of the skin. The rinsing method involved use of Thran ' s spray gun (Figure 1). It caused difficulties, partly connected with the mechanical operation of the equipment. Some of the test subjects developed severe erythema, which was possibly caused by Tween 80 and other inactivators in the rinsing fluid. Another difficulty arose from the need to sample with small volumes of rinsing fluid (10ml), because the numbers of bacteria taken up by larger volumes (100 ml) from the upper arm or abdomen were too small to be used in assessments.

I0 9 4

f 2

F igure 1. T h r a n sp ray gun . 1 = C o m p r e s s e d air entry; 2 = v a l v e ; 3 = e n t r y to spray head; 4 = exit f r o m sp ray head; 5 = air vent; 6 = s am p l ing fluid rese rvo i r (detachable) ; 7 = collect ing reservoir (detachable) ; 8 = special r u b b e r fastening; 9 = sp ray head (detachable) ; 10 = sealing band.

M a t e r i a l s a n d m e t h o d s

The swabbing method was used for sampling the skin. It involved wiping the skin with a swab moistened with t ryptone soya broth containing inactivators. As in the rinsing method, the skin areas sampled were 5 cm2; each of these areas was wiped for 10 s in different directions, using an

Skin d i s in fec t ion 53

approximately s tandard amount of pressure. T h e swabs were shaken in 5 mt t ryptone soya bro th containing inactivators. T h o u g h this me thod could not be standardized, the results of replicate tests done by the same trained person were reasonably comparable. T h e mean counts of viable bacteria obtained on sampling by this method were similar to those obtained with Th ra n ' s rinsing me thod (Table I).

"Fable I. Average viable counts of bacteria from skin samples: a comparison of the Thran and cotton swab methods

T h r a n C o t t o n s w a b

No . o f s a m p l e s 105 51 M e a n c f u / c m 2 ( r ange ) 1-1 x 10 3 2"5 x 10 3

(0-7 x 10 3) (0-5"1 x 10 3) Mean log cfu/cm 2 2.53 +0"94 2'36:t: 1-01

T h e site of sampling chosen was the upper arm, because (1) it is easily accessible, (2) it is large enough for a series of tests to be carried out on it with different times of exposure, (3) it is less subject to dis turbance f rom outside than, say, the lower arm, and (4) it is possible to keep the area covered for at least 24 h.

T h e exper iment was designed on the lines of the D G H M method for hygienic and surgical disinfection of the hands, i.e. the preparat ions to be tested were compared with those used in a s tandard procedure; in this s tudy either 60% or 70% isopropanol was the standard preparat ion used. Exposure times were 1 min, 10min, 1 h, 3 h, 24h, 3 days and 7 days. Prel iminary studies were made, as in the D G H M tests, on bacteriostatic and fungistatic action, on the inactivators chosen to prevent inhibi tory effects of antiseptic t ransferred f rom the skin and in vitro studies with bacterial suspensions.

Separate skin areas were used for pre-disinfect ion bacterial counts and for post-disinfect ion counts. As prel iminary exper iments have shown that brisk rubbing caused a reduct ion in the number of bacteria on the skin, friction was not used in applying antiseptic to the skin; this omission, though it caused a slight uncer ta inty with regard to the initial values, was considered necessary because the p re - t rea tment levels of bacteria on the skin were very lOW.

T h e main exper iments consisted of a comparison of 60% and 70% isopropanol with povidone- iodine (PVP-I ) solution (10%). Bacterial counts were obtained on swab samplings taken from the upper arm before and at the above-ment ioned intervals after disinfection. T h e disinfectant was applied with a swab and spread evenly over the skin. T h e difference between the log pre - t rea tment count and the log pos t - t rea tment count is the log reduct ion factor (RF), which was used as a measure of the degree of disinfection achieved.

54 K. O. G u n d e r m a n n e t a l .

._~

r~

z.o tl II II

1.0

0-5

II II IF

/ /

/

\ o /

\ /

B iI I I I I I I I II i II I I I I minlO min Ih 5h 24h 72h Iweek

Time

Figure 2. Comparison of the effect of 70% isopropanol ( 0 the skin flora.

0) and PVP-I (m - n ) on

R e s u l t s

T h e resul ts are shown in F igures 2 -4 and in T a b l e I I . Seven ty per cent i sopropano l was shown to be sl ightly m o re effect ive than 60% isopropanol , especial ly in a 10 rain exposure t ime, bu t the overal l effects of the two concen t r a t i ons of i sopropano l in the first 24 h were very similar. T h e effect of P V P - I t r e a t m e n t was a lmost ident ical wi th tha t of i sopropyl alcohol over the first 2 4 h . On longer ex p o su re the effects of each p repa ra t ion decreased. T h e d i s in fec ted areas cou ld no t be left unwashed , and c o n t i n u e d d is infec t ion by P V P - I cou ld be in fe r r ed f r o m the c o n t i n u e d presence of iodine s ta ining on the skin. In some e x p e r i m e n t s the counts of bacter ia f r o m the d i s in fec ted surface rose af ter 3 days to levels h ighe r than the p re -d i s in fec t ion values. Af te r 7 days they genera l ly c o r r e s p o n d e d with the p re -d i s in fec t ion counts .

2.0

S k i n d i s i n f e c t i o n

II II II II

55

1,5

g i.o

"u

0.5

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�9 A . ~, \ \

I l l t II I II L II t I rain t0 rain Ih 5h 24h

Time

-\

�9 . \ / I / - \ /

\ /

II t . . - ' H 72h .."

A'"

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I I week

Figu r e 3. C o m p a r i s o n of the effect of 60% i s o p r o p a n o l ( �9 ....... �9 ) and P V P - I ( I I - - - I I ) on the skin flora�9

T h e s ignif icance of the d i f fe rences b e t w e e n the effect of the d i f fe ren t p r e p a r a t i o n s was tes ted us ing W i l c o x o n ' s test for pa i r ed c o m p a r i s o n of l inked r a n d o m s am p l e s wi th a s ignif icance level of P = 0 " I in a one - t a i l ed test. T h e resul t was tha t the d i f fe rence was on ly s ignif icant at an e x p o s u r e t ime of 10 m i n b e t w e e n the 7 0 % i s o p r o p a n o l and the P V P - I so lu t ion . In each case, the s a m e test sub jec t s we re u sed for this c o m p a r i s o n , and b o t h p r e p a r a t i o n s were t es ted in paral le l on t h e m . At the o t h e r t imes , i.e. 1 ra in , 1, 3 and 24 h, as well as a f ter 3 and 7 days , the re were s l ight d i v e r g e n c e s in s o m e cases, b u t the d i f fe rences were not s ignif icant . N e i t h e r was the re a s ignif icant increase b e t w e e n e x p o s u r e t imes of 1 ra in and 10 ra in in the case of 7 0 % i sop ropano l . T h e d i f fe rence at an e x p o s u r e t i m e of 10 m i n b e t w e e n i s o p r o p a n o l and P V P - I is poss ib ly due to the chance se lec t ion of the tes t sub jec t s for this e x p e r i m e n t . I t was s h o w n tha t for p e r s o n s wi th a ve ry h igh initial bac ter ia l count , the effect of P V P - I was no t qu i t e as good as tha t of

56 K . O . G u n d e r m a n n e t a l .

2.0

L.5

c 1.0 O

0"5

II ....... II IL II II

I t ' " Ih 3 h

.& "~ . . . . ' "

] LI , I � 9 L 24 h ~'2 h . . - " I week

�9 . . . -

T i m e A"

Figure 4. Comparison of the effect of 70% ( � 9 ...... 0) and 60% ( � 9 ....... � 9 isopropanol on the skin flora.

70% isopropanol. However , fur ther investigations must be made to verify this statistically.

D i s c u s s i o n

In accordance with the results of the exper iments to date, a uni form test method for testing preparat ions for pre-operat ive and postoperat ive skin disinfection is proposed, for which the prel iminary exper iments would be carried out according to the D G H M method for the disinfection of hands. The preparat ions would then be compared with the effect of 70% isopropanol. For this, the investigations would take the form of the quantitat ive swab method, since this method is technically the simplest and also yields adequately reproducible results. It is proposed that the following test times be investigated: 1 and 10 rain for a short durat ion effect, and after

S k i n d i s i n f e c t i o n

Table I I. A comparison of skin disinfectants over 7 days

57

Log reduction factors with

Exposure 70% 60% 70% 60% time Isopropanol Isopropanol Isopropanol PVP-I Isopropanol PVP-I

1 min 1.58 1-45 1.58 1.36 1.45 1"36 10 min 1.58 1-35 1.58 1.06 1.44 1'06

1 h 1.51 135 1.51 1.39 1.35 1.39 3 h 1.27 1-24 1.27 1.16 1.24 1-16 1 day 1.19 1-59 1.19 1.56 1-49 1.56 3 days - 0' 13 0-02 - 0-09 0.14 0-08 0-14 7 days 0-26 0-28 0.18 0-63 0-43 0"63

24 h for a long d u r a t i o n effect. F u r t h e r e x p e r i m e n t s are n e e d e d to c l a r i fy w h e t h e r t he re is any p o i n t in t e s t i ng af ter 48 h. T h i s was no t i n v e s t i g a t e d in the e x p e r i m e n t s r e p o r t e d here , b u t it does s eem as if the bac t e r i a l c o u n t has a l r e a d y s t a r t e d to r ise aga in at th i s s tage so tha t , if r e q u i r e d , the a p p r o p r i a t e a reas of skin s h o u l d be d i s i n f e c t e d again af te r 24 h. T h i s a pp l i e s to b o t h i s o p r o p a n o l and to the P V P - I so lu t ions . T h e r e does no t s eem to be any p o i n t in c a r r y i n g ou t tes t s a f te r th is p e r i o d s ince the in i t i a l b a c t e r i a l c o u n t s are r e ached again in all cases a f te r 3 days .

R e f e r e n c e

DGHM (1981). Richtlinien f/Jr die Pr(ifung und Bewertung chemischer Desinfektionsverfahren. Erster Teilabschnitr Gustav Fischer Verlag, Stuttgart.