CA1152720A - Disinfection with isopropanol vapor - Google Patents

Abstract

ABSTRACT

A low temperature method for the cleaning and disin-fection of heat and liquid-sensitive articles that are brought into physical contact with patients during diag-nostic evaluation, surgery or therapy. These articles, such as endoscopes, bronchoscopes and related equipment are thus subject to contamination by microorganic pathogens and consequently may serve as transmittal agents for noscomial infection. In the method of this invention, quick, pene-trating and adequate disinfection can be obtained by the use of a vapor consisting essentially of from 40 to 100% isopro-panol and the remainder consisting predominantly of water vapor. The aforesaid articles are brought into direct contact and totally enveloping contact with the vapor at a temperature between 45°C. and 65°C. for a period effective to destroy the pathogens.
When the articles are then removed from vapor contact, any condensed isopropanol on the surfaces of the article quickly evaporates. This method can be operated in a disinfection chamber at constant atmospheric pressure or a vacuum can be drawn prior to introduction of the vapor into the chamber. disinfection generally results in from 1/2 hour to 1 1/2 hours, with shorter times possible in the vacuum cycle.

Description

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BACKGROUND OF THE INVENTION
Field of the Invention ~his invention relates to the disinfection of medical apparatus; more particularly to the disinfection of heat-and liquid-sensitive medical apparatus by the use of iso-propanol in the vapor phase.
Description of the Prior Art Conventional hospital sterilization practices call for the use of steam or ethylene oxide gas. There are limitations, however, on the types of equipment that may be subjected to these sterilants. Steam may cause damage to heat-sensitive materials such as plastics, rubber and the like. Ethylene oxide gas sterilization, while carried out at lower temperature s than steam sterilization, generally requires a relatively long aeration period or "turn-around time". Certain types of medical apparatus, especially expensive items, cannot be out of service for that period of time. As to this latter apparatus, when steam sterilization is also prohibited because of material limitations, the hospital generally resorts to the manual application of liquid disinfectants.
Even this procedure has serious drawbacks, however, because parts of an instrument being disinfected in such manner may be subject to chemical attack and/or other degradation by the li~uid disinfectant, especially when immersion is used as thc app ication technique.

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Specific types of medical apparatus that are not subject to steam and/or ethylene oxide gas sterilization for the reasons mentioned above include endoscopes, respiratory therapy equipment and anesthesia equipment, wrapped or unwrapped.
Endoscopes are instruments for the visual examination of body cavities, such as bronchoscopes, laparoscopes, arthoscopes, and upper and lower GI endoscopes. Fiberscopes or flexible fiberoptic endoscopes are those endoscopes having fiberoptic lighting; these are particularly adapted to bending and generally provide a brighter light than standard endoscopes. Endoscopic accessory or related equipment includes cytology brushes and biopsy forceps used in gastrointestinal endoscopy. The need for efficient and effective disinfection and cleaning of endoscopic equipment has been highlighted due to infections related to use of this ~ind of equipment in hospitals. Nosocomial (hospital-acquired) infections have been specifically associated with inadequately cleaned respiratory equipment.
~he Ad Hoc Committee of Infection Control in the Handling of Endoscopic Equipment, coordinated by the Association for Practitioners in Infection Control (APIC), in January 1978 established the following guidelines for the cleaning and disinfection of flexible fiberoptic endoscopes used in gastrointestinal endoscopy:

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"l. Scrupulous mechanical cieaning of insertion tube and channels, using a detergent, is imperative. This must be done immediately after use to prevent the drying of secretions.

2. Inspection of equipment for damage.

3. Disinfection of endoscopic insertion tube and all channels, performed with a chemical substance having disinfecting action sufficient to ki~ll all microorganisms (gram-positive and gram negati~e bacteria, fungi mycobacteria, and lipoph~ c and hydrophilic viruses~ except bacteri~al spores when used according to manu-factu~er's instructions.

4. ~de~uate rin$ing must follow such disinfection.

~t sh~uld be emphas~zed that adequate rinsing is necessar~ to prevent possible residual toxic e~fects of the disinfectant chemical and/or aetergent. The r;~sks of toxicity with regard to parti~cular disinfectants and/or detergents need further exploration.

5. The inserti`on tube and inner channels should be t~x~ughly and immediately air dried after cleani`ng and prior to storage. (Bacteria will mult~ply i'n a moist environment2.

6. Instruments to be stored.

7. Ethylene oxide sterilization is not generally p~acti`cal. If used, it is imperative that met~culous cleaning be accomplished as described in ~uideline 1, and that it be fol-lowed by adequate aeration.

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8. Because of the spring-like structural config-uration, accessories such as biopsy forceps and cytology brushes have been shown to be extremely difficult to clean and disinfect.
After immediate surface cleaning with a deter-gent/disinfectant, and rinsing, it is advisable to use either steam under pressure or gas Cethylene ox;de sterilization) or any other treatment wh~ch has the capability of penetrating the spring-like structures.

It IS emphasized that the heat treatments des-cribed be applied only to accessories such as ~opsy- forceps, not to fiberoptic devices.
Improved structural configurations of the accessor~es and~or more efficient cleaning methods- need further exploration."

These guideli~nes illustrate some of the special con-s~dexations and pro~lems ~n disinfecting flexible fiberoptic endoscopes (fiberscopes~. Liquid disinfectants, detergents, di~stilled water, steam and ethylene oxide gas (when pos-siblel, haye thus been used in ~arying combinations to acco~plis~ dis;nfection of this type of equipment. Even when d~si~nfecti~n has ~een adequate, time-consuming air drying is xe~u;xed ~nd ~nstruments are not immediately available for xe-use. Presently~, endoscopic equipment is either simply cleaned before re-use or is disinfected by immersion in some li~qu~d ~Qcl~dal agent. Simple cleaning is not an adequate process t~ p~qtect against cross infection. While dis-~n~ectin~ by immexs~on in a liquid agent can be effective, ~i~t does not permi~t packaging of the item to protect it from xec~ntaminat~on, i`n handl;~ng, transit or storage. Further-mo~e, rt o ten damages the device, and generally requires 4.

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copious rinsing with sterile distilled water to remove the residual agent before use. Additionally, immersion and rinsing are at the discretion of the worker and are frequently inadequate. Liqu~ds also exert a dissolving action on certain polyvinyl chlorides, silicones, acrylics, resins, lens cements and other materials of the endoscopes. De-tergents:can ~e abrasi~e and corrosive. The cumulative e.ffects dim~nis-h.the use-life of the equipment.
An ~ptimum cleaning and dis~nfection process for endo-scopes, .i~clud~ng fi~eroptic endoscopes and related equip-~ent, would thexefore incorporate the following features:
l. Operate at low temperatures 2. Operate at atmospheric pressure or below (vacuum) 3. Lea~e no resi`dual chemical 4. Provide moisture-free articles following disin-~ect~Qn 5. ~equire no aexation time 6. ~royide adequate penetratior. of springs and ~ntersti`ces ~y disinfectant 7. PxoYide adequate bactericidal action.
One Qb~ect~ve of this i~nvention, therefore, is.to proyi~e. a. ~u~ck, penetrating, low-temperature treatment of arti`cles ~t atmospheric pressure or ~elow (yacuum) which .: destroy$ ~i~nfect;~ous organ~sms, yields essentially moisture-: 25 f~ee a~ti~les without aerat~on t;me, and leaves no residual agent.
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Another objective is to provide an efficient and uniform treatment for all endoscopic (including fiberoptic) and accessory equ~pment, as well as for other articles which, cannot because of their structure or the materials of which they consist ~e sterilized ~y conventional methods, or cannot be disinfected ~y immersion. , Nathan U. S. Patent No. 867, 831 discloses the use of alcohol fumes- to sterilize beer vessels. The vapors con-dense w~thin a pressurized cham~er during sterilization.
The condensate will also dissolve resins formed in the beer-manufacturing process., These high pressure, moisture and resi~n-diss~lvi~ng features, which are favorable to beer yessels, would damage endoscopic equipment.
Gibson U. S. Patent No. 246,494 uses alcohol vapors and steam to restQre feathers. This ~s also a high temperature, pressure process contraindicated for endoscopes.
~artner U. S. Patent No. ~03,853 teaçhes the use of a methyl alcoh41 ~n approximately 55% concentration or ethyl , alc~h~l and ~ater vapor in large quantities. The sterili-zat,i~o,n cycle comprises essentially the following steps: (1) exhausti~on of a steril~zation chamber to a pressure-gauge yacuum of 7QQ mm; (,2~ introducing a mixture of water and methy1 a,lc~hol ,i~to the chamber and vaporizing the same;
(31 a timed exposure (e.g., about 20 minutes~ after vaporizatior i`s co~pleted; (4) admission of air to atmospheric pressure;
~51 all valved access to the chamber is closed and temperature is m,ai~ntai~ned constant for 1 1/2 hours from initiation of treatment; and, finally (6) a half-hour sweep of a strong cu~rent of air through the chamber. The articles are preferably 6.

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subjected to pressure after completion of this complicated cycle. The teaching emphasizes the importance of large vapor quantity and exhausting the chamber of air to a high degree before introducing the disinfectant in order to accomplish disinfection. -Thus biocidal activity is de-pendent on laxge quantities of alcohol and water vapors operating under a high vacuum. At 55% concentration, vapor biocidal activity without this extremely high exhaustion would be inadequate for disinfection. The large vapor quantities required would also penetrate and exert haxmful dissolving action on synthetic endoscopic materials.
Thus the alcohols and methods of these patents are unsuitable for disinfection of endoscopic equipment in ~.odern hospital practice.

SUMMP.RY OF THE INVENTION
A process that is suitable or the disinfection of such heat-sensitive and liquid-sensitive hospital equipment has now been found to comprise the topical employment of vaporized isopropanol usually in admixture with water vapor in preferably minor ~roportion. The term "heat-sensitive"
as used herein refers to materials or articles which cannot be exposed to a temperature greater than 150F. (65.56C.).
"Liquid-sensitive" as used herein refers to those materials or articles which are adversely affected by contact with liquids. The process of the present invention may be applied to any medical item or device that heretofore could not be sterilized at all; items which could not be sterilized routinely after each use; or those which need not be sterilized but only disinfected.

~ Z72~) A process that is suitable for the disinfection of such heat- and liquid-sensitive hospital equipment has now been found to consist in the topical employment of vaporized isopropanol usually in admixture with water vapor in pref-erably minor proportion. While isopropanol has been known as a strong liquid disinfectant, its solubility in water permitting its easy dilution, its high molecular density in liquid phase and its resultant propensity to attack components of the aforesaid heat- and liquid-sensitive hospital equipment such as endoscopes had limited its usefulness for such disinfection. Thus, even though isopropanol in the liquid phase is known as a disinfectant (see for example U.S.
Patents Nos. 2,832,664 and 3,992,147; ~or the liquid steril-ization of surgical catgut and seed husks, it was found to be incompatible with such sensitive articles of hospital equipment as endoscopes. For example, when the synthetic (i.e. plastic or elastomeric) materials of the endoscopic instruments are placed in the high density liquid environment, liquid isopropanol or other alcohol will be absorbed into the plastic indefinitely until the plastic is saturated with the liquid, resulting in damage to the material. The plastic (synthetic resinl is dissolved by the action of the liquid alcohol, and components and additives of the resin (silicone, polyvinyl chlorides, resins, cements, acrylics, polycarbonates, etc.) are leached into solution.
On the other hand, isopropanol vapor will not leach these materials. The maximum e~fects would be swelling from absorption of the vapor with subsequent recovery when removed from that environment.
The process of the invention comprises as a first step generating isopropanol vapor from a solution of isopropanol and water. Small volume percentages of butanol and morpholine also may be added to the solution. ~he concentration of isopropanol may range from 40 to 100% isopropanol, with an optimum concentration of 70%. The vapor is generated at a temperature in the range of 45C. to 65C., a preferred temperature being about 55C., that is, sufficiently high to produce a significant vapor pressure, but below boiling point so that equili~rium is reached. The vapor is intro-duced into a chamber in which the articles to be disinfected are placed. The cycle may be run at atmospheric pressure or a vacuum (from about 25 to 35 mm. mercury absolute) may be drawn in the chamber prior to introduction of the vapor.
Articles are exposed to the isopropanol vapor until disin-fection is achieved. This may be in 4 minutes, and does not e~ceed two hours. At the end of the cycles, the vapor is exhausted from the chamber. There is no need for aeration;
vaporization will flash off any condensed isopropanol.
There is generally no residual agent; if any possible agent remains it would be negligible in amount or effect.

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DESCRIPTIO~ OF THE PREFERRED EMBODIMENTS
optimal conditions for isopropanol vapor phase disin-fection are 70% by volume isopropanol and 30% by volume water at 55C. The effective temperature range for the process is based on a maximum temperature, about 65C.
(determined by the heat resistance of the article) and a minimum temperature, about 45C., below which impractically long exposure times are required. The temperature of 55C.
(131F.) was selected because vir'tually all synthetic (plastic/elastomericl materials commonly used in endoscopic equipment are stable and unaffected by that temperature~
The 70% by volume isopropanol/ 30% by volume water mixture is selected because this is the mixture most readily avail-able. Higher concentrations will follow chemical and biocidal kinetics with a modest increase in activity u2 to 100% by volume isopropanol and a rapid decrease in activity occurring at less than 40% by volume isopropanol in 60~ by volume water. Small volume percentages of butanol (e.g., up to about 6~) and/or morpholine (e.g., up to about 5%) when added to the isopropanol/water mixture tend to increase the biocidal activity of the vapor.

Example Tests were conducted under the just-described conditions by placing an amount of the isopropanol/water mixture in a stexilization chamber substantially in excess of that needed in order to ensure vapor phase saturation.

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115~720 The organisms used in the tests were Pseudomonas aeruginosa and Staphlococcus aureus. Glass plates and penicylinder carriers were innoculated from a broth culture to a population of 108 organisms per carrier, which provided a condition of high population of resistant organisms protected by much organic debris. Penicylinder carriers are standard challenge detectors, used in hospital steril-ization "packs" (packages of wet or dry, hard or soft goods or articles to be sterilized) to determine the bacteria ~ill achieved in a cycle. Penicylinders are a testing requirement to satisfy the EPA relative to the effectiveness of a disinfecting agent.
Plate carriers were exposed in uncovered petri dishes.
Isopropanol vapor phase disinfection was then carried out in an atmospheric cycle. The isopropanol-water mixture was vaporized into a closed chamber, at atmospheric pressure, for 16 minutes.
Other plate carriers of the same organism populations were again exposed under the same conditions of temperature and concentration. This time, the vapor phase disinfection was run in a vacuum cycle for 16 minutes. A vacuum of approximately 28 inches of mercury was drawn in the closed chamber and then the isopropanol-water mixture was vaporized into the chamber and pressure restored to atmospheric.
After exposure, each carrier was cultured separately to determine if all the carrier organisms were killed. Table A
gives the results of these experiments as a function of exposure time, and also indicates the comparative effective-ness of the atmospheric pressure cycle and the vacuum cycle.

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TABLE A
10ORGANISMS ON GLASS PLATE: .
55 C. 70% V~V ISOPr~oPANOL, 3096 V/V WATER
VACUUM CYCLE
Organisms Surviving Time P. Aeruginosa S. Aureus . .
8 Minutes .O TNTC*
16 Minutes 0 10 ATMOSPHERIC PRESSURE CYCLE
4 Minutes TNTC TNTC
16 Minutes O TNTC

* - Too numerous to count .
The results shown in Table A indicated that Pseudomonas aeruginosa was the least resistant organism and it was therefore dropped from further tests. In the subsequent experiments reported below in Table B, only Staphlococcus aureu , was innoculated in a 108 population per penicylinder carrier, this micro-organism being especially suitable for testing inasmuch as it is the resistant pathogen commonly found to be the causative factor in nosocomial infections. Again, six carriers were exposed in an open petri dish and six were exposed sealed in a "peel pouch". A 70~ by volume isopropanol and 30% by volume water mixture was placed in the chamber in an amount in excess of that calculated to ensure vapor phase saturation. The mixture was vaporized in the chamber at a temperature of 55 C. The experiment was run in a substantiall atmospheric pressure cycle, and then duplicated in the vacuum cycle. Table B shows the results, again as a function of time, with a comparison of atmospheric pressure and vacu~m cycles:

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: S. AUREUS, 108/CARRIER
55 C. 70% v/v ISOPROPANOL/30% v/v WATER
VACUUM CYCLE
Time Bare Pouch _ 16 Minutes 5 of 6 Positive Growth 6 of 6 Positive Growth 32 Minutes 2 of 6 Positive Growth 1 of 6 Positive Growth 32 Minutes All Negative Growth All Negative Growth 32 Minutes All Negative Growth All Negative Growth 64 Minutes All Negative Growth All Negative.Growth 64 Minutes All Negative Growth All Negative Growth 64 Minutes All Negative Growth All Negative Growth 70 Minutes All Negative Growth All Negative Growth ,,, , ., i ATMOSPHERIC PRESSURE CYCLE ,.
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Time Bare Pouch 32 Minutes 5 of 6 Positive Growth 6 of 6 Positive Growth 64 Minutes 2 of 6 Positive Growth 3 of 6 Positive Growth 100 Minutes 1 of 6 Positive Growth All Negative Growth 10~ Minutes 3 of 6 Positive Growth 4 of 6 Positive Growth 128 Minutes 1 of 6 Positive Growth All Negative Growth 128 Minutes 6 of 6 Positive Growth 5 of 6 Positive Growth 128 Minutes 4 of 6 Positive Growth 5 of 6 Positive Growth 128 Minutes All Negative Growth All Negative Growth 160 Minutes All Negative Growth All Negative Growth . 160 Minutes All Negative Growth All Negative Growth 527ZI) The above Tables thus indica~e that adequate disin-fection with a bacteriological kill greater than 50% can be obtained in from 64 to 100 minutes (1 to 2 hours); and complete sterilization in from 128 to 160 minutes (2-3 hours). .
Utilizing the features of isopropanol vapor compatible with heat and li~uid sensitive equipment such as endoscopes, as discussed above, and the disinfection/sterilization data of the test results, it is possible to achieve an effective disinfection cycle for this type of equipment by the use of .
isopropanol and water in the vapor phase.

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of disinfecting heat-sensitive or liquid-sensitive articles that are brought into physical contact with patients in the course of examination, surgery or therapy and that consequently are subject to contamination with microorganic pathogens, the said method comprising:
bringing such article subsequent to exposure to any such contamination into direct, sustained and totally enveloping contact with a substantially liquid-free vapor at a pressure not substantially exceeding atmospheric pressure, said vapor consisting essentially of from 40% by volume to 100% by volume of isopropanol and the remainder consisting predominantly of water vapor;
maintaining said contact at a temperature between about 45°C and 65°C for a period effective to destroy said pathogens;
removing the said article from contact with the isopro-panol-containing vapor; and allowing any condensed isopropanol on the surface of the so-treated article to evaporate from the said surface.

2. The method of claim 1 wherein the concentration of isopropanol is about 70% by volume and the concentration of water vapor is about 30% by volume.

3. The method of claim 1 wherein the pressure of the disinfecting vapor is substantially atmospheric.

4. The method of claim 1 wherein there is a vacuum from 25 to 35 mm. mercury absolute drawn from the atmosphere surrounding such article prior to introduction of the isopropanol-containing vapor.

5. The method of claim 1 wherein the temperature of the disinfecting vapor is about 55°C.

6. The method of claim 1 wherein the disinfecting vapor is at a subatmospheric pressure.