ULTRAVIOLET AIR SANITATION Destruction of Microorganisms FREDERIC W. ROBINSON Hanovia Chemical & Manufacturing Company, Newark. N . J.
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MPROVEMENT in our methods for sanitation, especially of food and water supplies during the past haif century, has brought with it marked reduction in sickness and in the death rate from diseases affecting the intestinal tract. This steady improvement in health standards has perhaps contributed to an almost entire neglect of sanitation in the air we breathe. It is bighly significant, therefore, to find from authoritative statistics that as high as 85 per cent of the deaths from infections and parasitic diseases are caused by microorganisms whose normal portal of entry is the upper respiratory tract. The recent high rate of comuieroial development of airconditioning equipment and improved methods of air bacteriology have served to focus attention on the subject of air
if the aims and p&poses of ultraviolet
air sanitation are 6rst defined. Air sanitation is closely analogous to water sanitation; its purpose is s u b stantially the s a m e t o make the air in confined spaces more safe under the particular circumstances of its use, and to guard against the possibility that air-borne organisms may cause clinical infections. Such applications may vary greatly in their technical details according to the type of problem presented. Most cases will fall into one of the following categories.
Infection by Sedimentation Inhibited In hospital opcrating room the primary objective is to reduce the risk from pathogenic organisms settling from the air on the surfaces of open incisions, on instruments, or on the hands of the operating personFLOOR&ASD T Y P ~ OF LAMP ne1 from which they might be transferred into open wounds. Protection of perishable foodstuffs against contamination from air-horae organisms is a further example. Meleney ( U ) ,Hunt (8, Beck (a), Hart (6, 7), and others have clearly recognized the lack of adequate air sanitation in the hospital operating room. One may quickly determine hy exposing blood agar plates how many bacteria may be expected to find their way hy sedimentation on to an area of any given size during any given time in the operating room. Hunt (8) reported that in a modern operating room using every reasonable precaution to ensure asepsis, but without ultraviolet, considerable numbers of bacteria may be collected from the air by sedimentation. A 10O-mm. blood plate exposed for 1 hour and incubated for 36 hours showed eighty-six colonies, seventy-six colonies, and seventy-eight colonies, respectively, on successive days. In another case thkty colonies were found. R. G. Urquhart (3) found an average of forty-eight colonies in a series of exposures of 45 minutes each (Figure 1). These figures are in close agreement with conditions found in other institutions. Hunt estimated, from a survey of other publications and from his own experience, that 10 per cent expresses conservatively the
ULTRAVIOLET O N ORGANISMS SPRAYED imo THE AIR ON ONE SIDEOF L.4m BARRIER AND COLLECTED FRO= THE Ant ON THE O'THER SIDE
EFFECTOF
Lamps alternately turned off and on.
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48 17
I5
I2
0
0
0
I.
2.
3.
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EFFECTOF ULTRAVIOLET ON BACTERIAL CONTAMINATION OF AIR IN A HOSPITAL FIGURE 1.
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OPERATINGROOM
Blood agar plates exposed an avera e of 45 minutes on o erating and sappyy tabyes.
(Above) A , Four ultraviolet tubes two positions
B . Four ultraviolet tubes: four positions 1. Supply table
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2. Instrument table
Courtesy, Department of Surgery, State of Connecticut Tuberculosis Sanatoria
3. Operating table 4. Operating room (Numerals above circles indioate number of oolonies)
(Right) Colony Counts (Average) : 1. Without ultraviolet ray
2. With four ultraviolet tubes in two positions
3. With four ultraviolet tubes in four positions
average morbidity from operative wound infections a t the present time. Fortunately most of these are mild and superficial and last but a few days. Whether mild or severe, if some of these infections may be prevented by better air sanitation, the patient should have the benefit of this added protection. In a typical case (3) with a properly engineered installation of four small ultraviolet fixtures using a total of 120 watts of electrical current, a reduction of between 80 and 90 per cent in the number of bacteria collected by sedimentation was shown. No inconvenience to the operating personnel results; the fixtures are mounted on the walls a t ceiling height or about 14 feet from the floor where the operating room is of the amphitheater type, and the entire air contents of the room thus come under the influence of the ultraviolet. The quartz low-pressure discharge tubes used for this purpose emit approximately 95 per gent of their total ultraviolet output in the wave length 2,537 A., which is a t the peak of the bactericidal efficiency curve as shown in Figure 2. It is important to use lamps of the filter-jacketed type. The filter jacket screens out all radiations shorter than 2,200 A. and by this means prevents the production of ozone which otherwise would result. The very purpose of air sanita.tion makes it necessary to avoid excessive ultraviolet intensities. The amount of ultraviolet which may fall on the patient during the course of the operation should be kept sufficiently low so that no reaction will be caused in the tissues exposed. It is recommended that plain glass spectacles or cellophane
visors be issued to the operating personnel, either of which has been found to give adequate protection to the eyes.
Prevention of Cross Infection In infants' nurseries, school rooms, and hospitals for contagious diseases the primary objective is to prevent cross infection through interchange of nasopharyngeal flora.
I00 80
60 40 20
2400. 2 6 0 0
2800
3000
ULTRAVICCET WAVELENGTH IN ANGSTROMS.
FIGURE 2.
BACTERICIDAL EFFICIENCY CURVEFOR B. coli (6)
In the study of diseases whose normal portal of entry is the nasopharynx, it is difficult to determine the bacterial contamination of the air. I n that case one should know the total number of bacteria present in the air, and this, as Wells (I?') showed, may be many times greater than the number which may be collected by sedimentation. In one experiment
JANUARY, 1939 welve out of fifteen plates remained negative when exposed for 15 minutes in air containing twenty-five B. coli per cubic foot. The use of an air centrifuge or other adequate method of assay seems almost imperative, therefore, in studying air contamination in relation to respiratory infections. I n m a n y cases in this categofy, sanitation of the air is rendered more difiicult by the fact that long exposures of the eyes would result in severe cases of conjunctivitis. This may he prevented by the use of indirect fixtures so arranged that (a) the eyes are effectively guarded at all times, and (b) adequate air sanitation is still provided. In the M a r l b o r o S t a t e Hospital, Marlboro, N. J.,a group of patients has been living 24 hours a day under ultraviolet air sanitation for 4 months without the development of any subjective symptoms. Several important studies in air sanitation 8s applied to rooms under more or less permanent occupancy were reported by Wells (16,16) and Vonder Weidt (14) xhicb demonstrate that great improvenient in air sanitation results when ultraviolet is employed in a well-designed installation. The technique of ultraviolet air sanitation in its relation to isolation wards for contagious diseases is under study by McKhann (10). He found that a light barrier set up in the corridor between wards may be made practically impervious to air-borne bacteria carried by ordinary ventilating currents. McKhann sounds a note of warning which is important in all air sanitation problems involving more or less periiianently inhabited rooms, hospital wards, school rooms, hospital reception rooms, etc. He points out t.hat, since the ultraviolet equipment must be so installed as t.o protect the eyes of those in the room (cotniiionly, indirect lighting fix-
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tures above eye level), the radiation serves tu dilute the contaminated air with sterile air, and thus reduces but never completely eliminates the contamination so long as infectors remain in the room. With suitable design, however, installations with indirect lighting of this type may he made to show a degree of air sanitation equivalent to one hundred to five hundred or more complete turnovers of air per hour (16). Widespread application of this principle in the rooms where perishable food products are packed is an obvious and logical anticipation, but on the basis oi present knowledge there is no basis for the belief that foodstuffs other than clear fluids may themselves he effectively and eeonomically sterilized by iiltraviolet. For the past ten years it has been known that by painstaking irradiation the growth of mold on bread may be inhibited by from 24 hours to several days, but so far, huyers have not been found willing to pay a premium for stale bread. The process is therefore definitely limited by its lack of economic advantage.
Sterilization of Air Supply Compressed-air systems are employed, for example, in the operation of bone drills, in 6lling sterile biological solutions into cont a i n e r s , or in pumping milk.
Sanitation in AirConditioned Systems 1x1 air-conditioned systems there are two types of cross infection to be guarded against-that which may arise within the room where an infector is located and the transfer of air-borne organisms from one room to another. The ability of ultraviolet rays to destroy bacteria was determined m a n y years ago. Domes and Blunt (4)
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made one of the earliest studies of this subject in 1877. Barnard and Morgan (1) in 1903 showed that the most effective rays were those between 2,265 and 3,287 4. wave length, In 1922 Klemperer and Kempner (9) showed that ultraviolet was able to free the air of bacteria; by eliminating the possible effects of ionization and ozone, they were able to show that this effect is due to a direct action of the ultraviolet on the bacteria. In September, 1925, a patent was granted to Napier (13) covering the withdrawal of air from a room and destruction of bacteria in the air by ultraviolet before its reintroduction.
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borne bacteria, he may refer to the presentation of this subject by Wells and Wells (17)whose experimental work laid a solid foundation for the whole subject of air sanitation. In conjunction with air-conditioning systems, ultraviolet air sanitation offers profound benefits. Since, with the exception of a few special cases, the economics of air conditioning demands a recirculation of a large part of the air, usually 50 to 90 per cent, the possibility of distributing air-borne organisms from one person to another can hardly be disregarded. In fact, this has in some instances prevented the installation of air-conditioning equipment.
INSTALLATION OB EQUIPMENT USEDTO’ DESTROY AIR-BORNEBACTERIA IN A MIDWESTERN HOSPITAL
Obviously in the sterilization of air supply, where all of the air is under control, it should not be difficult by the use of quartz ultraviolet discharge tubes to ensure complete sterility and to calculate the engineering design accordingly. In inhibition of infection by sedimentation and in the prevention of cross infection, however, since the bacterial contamination arises largely in the same chamber (from the noses and throats of the people in the room) in which the infected person is confined, complete sterility of the air becomes a hypothetical concept and possibly is not essential. While it is pertinent, therefore, to differentiate sharply between air conditions where one or more sources of contamination are contained within the chamber, and other conditions where this is not the case, the problem remains always to make the air in question as safe as possible for the purpose it serves. This constitutes the whole problem as far as it concerns us here. Unfortunately many misleading and sometimes entirely erroneous statements on this subject have been broadcast in the public press, and ultraviolet sterilization has been held out as a panacea in many and varied instances where its value is as yet unproved. As early as 1914 the treatment of freshly killed meat with ultraviolet was advocated by Monvoisin et al. ( l a )in order to sterilize the surface, but up to the present time no economic advantage of this process has been shown. Such promiscuous statements are to be deplored, since they naturally tend to retard the sound application of a principle which seems to hold great promise of benefit to the public health. Living microorganisms have been captured even in the stratosphere, and organisms characteristic of the respiratory mucosa have been recovered from the air in an airtight metal chamber 48 hours after inoculation. Should one be inclined to doubt the possibility of clinical infection resulting from air-
By the use of adequately designed ultraviolet installations mounted in the air ducts, satisfactory air sanitation has been provided in railway cars (16). Here the rate of circulation corresponds to twenty turnovers of air per hour. The rate of destruction of bacteria is dependent upon the rate of circulation; if the total rate of circulation is conspicuously lower than twenty turnovers per hour, some additional provision for ultraviolet radiation in the room would be essential for adequate air sanitation.
Literature Cited Barnard and Morgan, Brit. Med. J.,Nov. 14, 1903. Beck, W. C., Arch. Surg., 33, 876-89 (1936). Conn. State Tuberculosis Sanatoria, Dept. of Surgery, personal communication. Downes, A,, and Blunt, T. P., PTOC. Roy. SOC.(London), 26,488 (1877). Ehrismann and Noethling, 2. Hyg. Infektionskrankh., 113, 597 (1932). Hart, Deryl, Diseases of Chest, 111, No. 6,14,28 (1937). Hart, Deryl, Modern Hospital, 46, No. 6, 79-81 (1936). Hunt, E. L., New Engl. J.Med., 209,931-3 (1933). Klemperer, G., and Kempner, L. R., “Die Therapie der Gegenwart,” 1922. McKhann, C. F., Steger, Adelbert, and Long, A. P., Am. J . Diseases Children, 55, 579-99 (1938). Meleney, F. L., Surg., Gynecol., and Obstet., 60,269 (1935). Monvoisin, Barrat, and Robin, British Patent 22,669 (Nov. 17, 1914). Napier, F. L., U. S. Patent 1,553,098 (Sept. 8, 1925). Vonder Heidt, L. C., Modern Hospital, 51, No. 2,69-71 (1938). Wells, W. F., Ibid., 51, No. 1, 66-9 (1938). Wells, W. F., and Wells, M. W., Am. J. Pub. Health, 28, 343-50 (1938). Wells, W. F., and Wells, M. W., J. A m . Med. Assoc., 107, 16981703, 1805-9 (1936). RECEWED
August 26, 1938.
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