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FILE NAME Kent KNT DATE 1959 May 16 DOC KNT156 DOCUMENT DESCRIPTION Journal Article - Air Hygiene - The Journal of the American Medical Association 1959 ---- -- Annual Meeting Atlantic City + June 8-12 1959 This Issue Exceeds 170,000 Copies THE JOURNAL OF THE American Medical Association N. DEFENDANT'S ne EXHIBIT MAY 16 1959 ORIGINAL ARTICLES OP.F Ph.D. Lowe M.D. EFFECT A PRACTICAL DIETARY REGIMEN ON SERUM CHOLESTEROL LEVEL P. A. Boyer Jr. T. Ph.D. W. Gordier , and J. D. Ralston M.D. Indianapolis AIR HYGIENEFOR HOSPITALS Norway Dissecting Aneurysm Pyro- 25 7 zinoic Acid Amide and Cycloserine for Tuberculosis 356 Portugal Physiotherapy of Periarthritis 261 Spinal Amyotrophy Cryptorchism POISONOUS SNAKE BITES Thomas McCreary M.D. and Harold Wurzel M.D. Philadelphia MEDICAL CARE UNDER THE HEALTH INSURANCE PLAN OF GREATER E. F. Doily M.D. New York HOSPITAL A SMALL COMMUNITY J. E. SegraveM.sD. MEDICAL RESPONSIBILITIES HANDLES A DISASTER Chicago IN A CHANGING WORLD Gunnar LaCrosse Wis WHY CONFERENCE M.D. THIS CONFERENCE M.D. Brookline Mass WHY THIS CONFERENCE E. L. Stebbins M.D. Ballimore THE RISE OF SPECIALISM IN MODERN SOCIETY M. Gross Ph.D. Durham N. SPECIALIZATIPrOiNor AND THE Ph.D. PURSUIT Evanston III OF EXCELLENCE NEW YORK 268 272 277 280 283 284 285 289 Iron and Cobalt in Anemia 356 Sweden Combined Treatment of Tuberculosis Calcium Infusion Test for Sarcoidosis Prolapse of the Uterus Prolonged Blood Loss at Delivery Pregnancy The PrediabetPriedicabetic PePerriiood d and Obstetrics ... United Kingdom Little Donign eTrurm- peters Loud Notes Reactions of Pa tients Told They Have Cancer Mater- nity Hospital to Close .... 359 Correspondence - Medicolegal Abstracts ............. 361 . 362 Medical Film Reviews . 363 Medical Literature THE NATURAL HISTORY OF SPECIALISM IN MEDICINE 294 Medical Literature Abstracts 364 lage Galdston M.D. New York Book Reviews 391 THE THE CHALLENGE S. M. OF SPECIALIZATION Tenney Hanover N. K. IN BASIC MEDICAL SCIENCE EFFECT OF SPECIALIZATION ON GRADUATE Pearse M.D. Rochester N. EDUCATION IN SURGERY .. 298 301 Questions and Answers Leukemia After Imadiation Amebic Granuloma Use of Glucocorticoids MAINTENANCE EDUCATION E. L. OF STANDARDS IN GRADUATE MEDICAL Turner M.D. Chicago WORKSHOP CONFERENCE ON SPECIALISM IN MEDICINE 1. RESIDENCY PROGRAM Wright Adams M.D. Chicago and G. A. Wolf Jr. H.D. Burlington Yi THE SPECIALTY BOARD 2. J. PhPihillaaddeelplhpiahia and W. S. W. BaBnanks ks M.DM.D. . Chicago 3. THE RESIDENT AND FELLOW 4. A. THE M. Harvey MD HOSPITAL Baltimore and G. G. Reader M.D. New York J. C. Kinsey Ph.D. New York and J. F. Conlin M.D. Bocion wsssenmeesnntnnnsnn 310 313 315 317 319 Exchange Transfusions Transfusions Sterilization of Catheters Action of Testosterone Vita- min B Requirement lococcus . Requirement Carriers Testosterone Vita- Testosterone in Anemia Staphy- Preoperative Tubercu- losis Therapy Oral Treatment of Diabetes Duties of Operating Room Nurse . Watkins Transposition Transposition . Clothing Residual Nurse MusPatryalOysdios r of Facial Dermatis Facial Paralysis Contact Contact DermatDeirmattitiis s Postural Variations in Pulse and Blood DEFENSE THE ROLE OF MEDICAL EDUCATION IN CIVIL AND Postoperative MOBILIZATION Pressure 3 2 2 Genitourinary J. S. Patterson B.S. Washington D. Bleeding Pastoperative Cerebrovascular SPECIAL ARTICLE NOMENCLATURE OF BLOOD CLOTTING FACTORS DIAGNOSTIC PROBLEM Complications Cataracts Congenital 325 Anomalies Baldness Contact Lenses and Hy- P. Femur motitis Carcinoma and Thrombophle- PROGRESSIVE PULMONARY INSUFFICIENCY IN A YEAR WOMAN 328 bitis Shortened ... 395 D. S. Kushner M.D. and S. Szonio M.D. Chicago EDITORIALS WASHINGTON NEWS Strengthening Understanding ...... cee ORGANIZATION SECTION Denmark Hypofibrinogenemic Hemor- rhage in Pregnancy .. cssscssseeeeee Finland Tuberculous Laryngitis 17 3.50 Radiation Out Hearings Open Senate Group Approves International Re search Bill Flemming Asks Senate to Television Series in Atlantic City Golf Tournament in Atlantic City DEPARTMENTS REGULAR Government Services occ seeue Electroshock Hydroxycorticosteroid Psychic Levels After Disturbances After Thyroidectomy Gastroscopy Reticulocyte Reaction in Hypoxia 350 France Hospital Teaching Reforms Hold Line on HEW Spending House Yotes Extension of Law Admitting Aliens With TB FDA Plans Legal Move on P.R.N. Abuses wc Adv Page 27 Meetings ..8...0.. Adv Page 30 Correction News Examinations and licensure Congress of Allergists 351 Iceland Leprosy..... stems 351 Magazine Officers of M. A Report Adv Adv Page Page 40 52 Deaths seteeees Foreign Letters . i sufficiency in India Oxytocics Medical Supplies Planned Parent- From Other Pages Adv Page 58 Suggestions for Contributors Page 216 Canada Council on Hospital Accredita- hood Spinal Arachnoiditis Opera- Tonics and Sedalives Adv Page 220 tion Nutritional Deficiencies in Men- tions on the Heart Amebiasis Jaun- Customs and Idioms .Adv Page 234 tal Patients Surgical Results of Mitral dice Brucellosis Chloramphenicol in The Bright Side .Adv Page 258 Valvolamy District Care for Mental Patients Spinal Traction cco. Children Encephalilis ... . 352 Israel Uptake of Radioiodine 355 1 Books Received Advert..isers Index to Adv ..Adv ..Adv Page Page 264 272 Volume 170 No. 3 Published Weekly at 535 North Dearborn Street Chicago 10 Illinois Subscription 15 Single Copy 45 cents Ready Soon New 7th Edition of Nelson's Pediatrics Vol 170 No. 3 AIR HYGIENE 71/261 tion in blood cholesterol levels The dietary alteration was accomplished simply easily and inconspicuously and with an excellent degree of patient acceptability P. O. Box 1656 6 Dr. Boyer Dr. C. L. Williams Superintendent of Central State Hospital provided facilities for this study The com oil margarine used in this study was supplied as Emdee margarine by Pitman Company Indianapolis References 1. Role of Dietary Fat in Human Health Publication 575 __ National Research Council National Academy of Science 1958. Symposium on Fats in Human Nutrition Council on Foods and Nutrition J. A. M. A. 1890-1925 Aug. 24 1957. Katz L Stamler .; and Pick .: Nutrition and Atherosclerosis Philadelphia Lea & Febiger 1958 2. Enos W. F Holmes R. H and Beyer .: Coronary Disease Among United States Soldiers Killed in Action in Korea Preliminary Report J. A. M. A. 1090-1093 July 18 1953 3. Keys A. and Anderson J. T Relationship of Diet to Development of Atherosclerosis in Man Symposium on Atherosclerosis Publication 338 National Research Council National Academy of Science March 22-23 1954 4. Dawber T. R Moore F. E and Mann G. V Coro- nary Heart Disease in Framingham Study Am J. Pub Health 4-24 April pt 2 1957 Choles- 5. Rutstein D. D Ingenito E. F Craig J. M and Mar- tinelli M Effects of Linolenic and Stearic Acids on Induced Lipoid Deposition in Human Aortic Cells in Tissue Culture Lancet 545-552 March 15 1958 6. Margolin E. G Xanthoma Diabeticorum Ann Int Med 629-635 Sept. 1953 7. Kinsell L. W. and others Dietary Modification of Serum Cholesterol and Phospholipid Levels J. Clin Endo- crinol 909-913 July 1952 8. Hardinge M. G. and Crooks H Fatty Acid Composi- tion of Food Fats J. Am Dietet A. 1065-1071 Oct. 1958. Stefanik P. A. and Trulson M. .: Modifying Fatty Acid Content of Diet ibid 591-595 June 1958 9. Morrison L. M Nutritional Prografmor Prolongation of Life in Coronary Atherosclerosis J. A. M. A. 1425- . 1428 Dec. 10 1955 10. Kinsell L. W. and others Essential Fatty Acids and the Problem of Atherosclerosis Am J. Clin Nutrition 628-631 Nov. 1958 11. Keys A Anderson J. T and Grande .; Essential Fatty Acids Degree of Unsaturation and Effect of Corn ( Maize Oil on the Cholesterol Level in Man Lancet 66-68 Jan. 12 1957 12. Vail G. E Cooking with Fats High in Polyunsatu- rated Fatty Acids J. Am Dietet A. 119-121 Feb. 1959 13. Lewis L. A. and others Serum Lipid Levels in Nor- mal Persons Findings of Cooperative Study of Liproproteins and Atherosclerosis Circulation 227-245 Aug. 1957 14. Terman L. .: Dietary Management of Hypercholesterolemia Geriatrics 111-114 Feb. 1959 Loe AIR HYGIENE FOR HOSPITALS II EFFICIENCY OF FIBROUS FILTERS AGAINST STAPHYLOCOCCIC DROPLET NUCLEI AND BACTERIA DUST Henry F. Allen M.D. Boston There is general agreement that air supplied to delivery rooms operating rooms and nurseries should be free from dust and bacteria On the one hand pure air is needed to maintain dilution of air- borne contaminants derived from human sources inside these areas on the other hand the demon- strated fact that pathogenic organisms may enter such spaces via conditioning ducts must be guarded against by efficient cleaning of air supply To insure satisfactory performance over long periods devices for delivering clean air should be simple and trouble and should require a minimum of maintenance Recent developments in the field of air filtration permit realization of these ob- jectives at reasonable installation expense and low operational costs This paper reports studies of the arrest of bacteria particles by fibrous filters in experimental and actual situations From firmary School the bacteriology laboratory Massachusetts and the Department of Ophthalmology Eye and Harvard Ear InMedical A laboratory and operating room study shows that it is possible to provide absolute filtration of bacteria on dust particles and high retention of bacterial droplet nuclei through installation of certain deep glass material in the hospital ventilating system A asbestos paper offered retention in the some range No hospital should accept an installation which has not been found to retain at least 85 of at- mospheric dust or its equivalent Careful performance testing of the installation is essential Bacteria in air occur as droplet nuclei or are attached to minute particles of dust lint or skin The former are produced by the atomization of re- 72/262 AIR HYGIENE J.A.M.A. May 10 1959 spiratory secretions as during talking laughing coughing or sneezing These droplets approximate 10 in diameter and evaporate almost instantly in air of a relative humidity of less than 100 The droplet nuclei which remain after evaporation consist of one or more bacteria with a coating of dried organic material They are usually between 1.34 and 2.68 in diameter * and settle at an average rate of 0.04 ft per minute in still air As convection cur- rents tend to keep room air in constant motion bacterial droplet nuclei tend to remain in a state of continuous suspension bearing dust particles are thought to vary greatly in size and to be much larger than droplet nuclei Most of them settle at 1 or 2 ft per minute in still air but some may be continuously suspended in moving air may be bonded together by phenolic resins or papers of cellulose and asbestos glass glass and asbestos or ceramic fibers with or without a binder A great increase in filtering surface can be achieved by pleating these materials Air velocities through the medium usually range from 5 to 25 ft per min ute In general units presenting a superficial area of 4 sq ft provide an air flow of 1,000 cu ft per minute at an average duct velocity of 250 ft per minute Retention of particles by these mediums is largely the result of inertial impaction of particles on fibers In addition the static gas film around fibers may interfere with the passage of particles Although physicians do not ordinarily carry out performance tests on air filters an understanding of the basis for efficiency rating is important This is because a filter which is highly efficient against Fig blower system 1 nitrogen supply line 2 flow regulator 3 DeVilbiss 40 nebulizer 4 location of dispersion disk 5 sampling point MF holder 6 mercury manometer 7 vacuum pumps 8 filter medium in holder 9 water manometer 10 filter holder 11 fan 12 calibrated bag not used during tests 13 wet and dry bulb thermometers gauge Ventilating air is cleaned by passage through devices which operate on one of the following principles 1 impingement on mediums coated with viscous material 2 impaction on fine fibers of dry porous mediums 3 electrostatic precipitation or 4 washing or scrubbing by passage through wet cells or fine sprays The antibacterial efficiency of viscous and wet cell filters is too low to warrant their use in critical hospital arcas Electronic air cleaners have been reported to possess high efficiency against air- borne bacteria and viruses but will not be discussed in this paper Fibrous filters may be made of fabric mediums of wool felt or cotton batting or cloth deep mats composed of glass fibers averaging between 0.8 and 3.0...in diameter which particles 10... in diameter may be extremely inefficient against particles l in diameter A case in point is the poor performance of viscous filters against atmospheric dust Deep mats composed of glass fibers averaging between 0.8 and 3.0 in diameter are rated by the National Bureau of Standards NBS discoloration test with atmospheric dust used as the test material that is against particles averaging 0.5 in diameter Their efficiency increases with the useful life of the filter as particles build up on the filter face Efficiencies from 35 to 95 over the life of different grades of filters are achieved at the rated velocity The initial resistances of the various me- diums range from 0.14 to 0.48 in water gauge at the rated velocity Vol 170 No. 3 AIR HYGIENE 73/263 Paper filters are rated by the NBS discoloration test or in terms of their efficiency against dioctyl phthalate DOP smoke an aerosol of particles uniformly 0.3 in diameter Absolute filters achieve a minimum guaranteed arrest of 99.95 against DOP smoke Their retention of bacteria approaches 100 This high efficiency is obtained at the cost of in- creased resistance to air flow Experimental Studies There are few studies of the efficiency of fibrous mediums against organisms Decker and co- workersfiber tested the efficiency of three grades of fiber pads and of two types of mineral papers against freshly atomized aerosols of Serratia indica and Escherichia coli T bacteriophage A singlethickness pad possessing the characteristics of Fil- terdown FG retained 99 of the bacteria and 98 of the bacteriophage Penetration of the glass- asbestos paper was 2.8 to 14 per 10 million organ- isms of type E glass paper 1 to 2 per 100 million organisms The downstream section of the filter holder in- corporated a fine stiff stainless steel screen to pro- vide backing for the filter medium being tested The screen was soldered to the flange and the interstices of the meshwork were filled with aluminum powder in a plastic base so as to present a flush smooth border 1.25 in wide around the periphery of the filtering surface A gasket of spun glass fiber was cemented to the downstream flange and one of 0.12 foam rubber to the upstream flange Clamps were used to maintain firm pressure through the opposed flanges on the filter medium : between the gaskets The ducts were equipped with dispersion disks located five duct diameters upstream from each sampling point to provide thorough mixing of the aerosol before sampling The sampling points were located 20 in downstream from the intake and from the filter holder respectively All joints were made airtight with sealing tape Air samples were taken through angle glass tubes 6 to 8 mm in diameter inserted through the TABLE Characteristics of Fibrous Filter Materials Code Trade Name Material Diameter of Glass Fiber Emciency % ... B. Ceram- le FG ... ... CH Micretain Fiberfrax Filterdown Aerosolve 95 Aerosolve 85 Glass paper asbestos paper Aluminum silicate paper Glass mat Glass mat 9 Glass mat 1.0 1.0 2.4 1.25 1.0-1.1 0.8-0.9 * During useful life of Alter Dioctyl phthalate 0.3 # smoke $ National Bureau of Standards discoloration test $ At rated velocity 93.97 95 83 90-95 90-95 80-65 Rating Test DOP DOP DOP NBS NBS NBS : Rated Velocity Ft per Blin Pressure Drop 10. H Efficiency vs. Bacterial Droplet Nuclei % Efficiency vs. Dustborne Bacteria % 5.5 0.90 99.97 100 5.0 0.40 96.7-98.1 100 5.0 21.0 23.0 25.0 0.18 97-98 99 0.48 87-99 99 0.35 89-98 99 1-670 5-1-69 vee Because the bacterial species used by these workers is particularly vulnerable to drying and because neither it nor the bacteriophage is likely to be encountered in environmental air it seemed de- sirable to confirm these studies and to extend them to a pathogenic species more resistant to drying to bacteria attached to dust particles and to other filter materials At the same time an opportunity was afforded to compare two sampling techniques in the light of newer knowledge regarding one of them With these purposes in mind the following test situation was established Materials blower system was adapted for bacterial sampling of air upstream and downstream from the filter medium The assembly fig 1 consisted of several feet of round galvanized sheet metal duct 2 in in diameter a filter holder com- posed of two sided funnels with flanges by means of which the funnels could be clamped base to base and a fan at the downstream end of the system The filtration surface was 6.5 in on a with an area of 0.29 sq ft side duct wall and pointing upstream in the center of the duct The air was sampled for bacterial content either by filtration through cellulose ester gel mem- branes Millipore filters MF or by bubbling through critical orifice liquid impingers containing 200 cc of 3.2 heart infusion with 0.2 gela- tin solution the stem being 4 cm from the bottom of the container The pH of the impinger fluid was 7.2 A loopful of a silicon antifoaming agent Anti- foam A was added to each impinger Sampling rates were 2.0 to 4.5 liters per minute a pressure drop of 24 in Hg being maintained across the critical orifices during operation The dimensions of the sampling tubes were selected to make the sampling velocity approximately isokinetic with the central duct velocity Fresh aerosols were produced by atomization of bacterial suspensions from a DeVilbiss 40 nebulizer activated by nitrogen from a commercial cylinder at a Bow rate of 6.4 liters per minute hour broth cultures of Staphylococcus aureus Food and Drug Administration strain 209 American Type Culture Collection 6538 were diluted with sterile 74/264 AIR HYGIENE J.A.M.A. May 16 1959 distilled water to a degree suitable for sampling after nebulization The organisms were less than lu in diameter and were highly dispersed Dry aerosols were produced by insufflating fine dust obtained from the filter cones of ward vacuum cleaners into the duct from a powder blower These coated cones retain almost 100 of airborne bacteria contacting them The principal species recovered from this dust were represented by strains of yellow and white staphylococci hay bacilli sarcinae and assorted molds It is probable that the bacterial particles were not in a state of high dispersion in these aerosols The properties of the several filter materials samples tested are shown in table 1. At least three from one or more lots of each medium were tested and at least three trials were made with each sample Operation humidity of the room air was adjusted to the desired level by allowing steam to flow from the chamber of an autoclave into the room The rate of air flow through the system was adjusted by controlling the fan speed to produce the desired velocity at the filter face Flow rates Table Retention of Nebulized Staphylococci by a Single Pad of Filterdown FG Colonies Sampler Upstream Mulpore Alter oe 257 Impinger ..,.......cceesescesceees Implager Millipore filter ......... 920 3.57 per Literi Downstream 3 0.1 Par Temperature 23 C relative humidity 31 Sampling rate 2 liters per minute Efficiency T Efficiency 5.68 12.93 were measured directly by timing the inflation of a calibrated bag of weight polyethylene capacity 5.5 cu ft fig 1 With air flowing through the system at the desired rate fresh or dry aerosols were introduced at the intake and allowed to flow for from 1 to 30 min- utes before sampling was begun Sampling was carried on simultaneously at the upstream and downstream sampling points usually for 60 seconds At the end of each run the filter membranes were transferred to the surface of trypticase soy agar plate or aliquots of the impinger fluid were filtered through Millipore filters HA type which were incubated on the same solid medium After incubation of the plates at 37 C for 24 hours and 22 C for 12 hours colonies were counted under mag- nification using the ophthalmic biomicroscope and slit lamp Zeiss Opton Conditions and Controls The temperature dur- ing these experiments varied from 21 to 24 C the relative humidity was adjusted between 31 and 71 The construction of the system insured that no Organ- room air was drawn into it or the samplers other than that which was introduced at the intake _ isms present in the room air were not of the test species and were numerically insignificant in pro- portion to those in the artificial aerosols and their occasional presence appeared to have no effect on the results In a representative number of trials but not in all the filters and the downstream sections of the filter holder and ducts were sterilized by hot air between tests Failure to sterilize them in other trials ap- peared to make no difference in the results of these tests presumably because the test organisms were not present on or were not liberated by blow from the filter pads or the interior surfaces of the ducts in significant quantities The sampling mem- branes were sterilized by autoclaving The experimental techniques used in this study are described more fully in the first paper of this series At the relatively low filtration velocities and the relatively small sampling volumes used in the present study there was no evidence that vari- ation of the relative humidity within the range re- corded above had any effect on either the efficiency of filtration by the glass materials or the recov- ery of organisms on the sampling membranes MF In contrast to conditions in the former study " there was no warming or drying of air during its passage through the blower system Humidification of sampled air by passing it through 18 by in tubes containing rolled moist filter paper failed to increase the yield of organisms on the MF in com- parative tests with air of 39 relative humidity at a sampling rate of 2 liters per minute There was no evidence of increasing penetration of the fibrous materials with time Rather it was clear that accumulation of dust on the filters in- creased their retention of bacteria Filterless trials indicated an expected recovery rate of 90 or better at the downstream sampling point No correction for this factor was made in calculating efficiency of filtration oo 1 Results findings recorded in table refer to retention of bacterial droplet nuclei by new unused filter materials in terms of the dry aerosol assay Millipore filter sampling technique When parallel sampling by this method and by liquid impingers operated at an identical rate 2 liters per minute was conducted simultaneously at both the upstream and the downstream sampling points impinger counts were 3.3 to 3.57 times those on the MF at the upstream point and 2.75 to 2.9 times those on the MF at the downstream point In spite of the threefold disparity in absolute values filtration by the glass medium demonstrated by both methods was of the same order of efficiency It is presumed that the larger number of organisms recorded by the impinger represents both break of bacterial aggregates by it and decay of organisms after con- tacting the MF surface The former factor could account for the slightly higher efficiencies demon- strated by the impinger technique since aggregates Vol 170 No. 3 AIR HYGIENE 75/265 which would produce only a single colony on the MF would presumably be arrested by the glass filters more readily than single cells The fact that the efficiency of the more retentive materials appeared nearly the same by both methods is consistent with monodispersion of the particles in the aerosol A typical trial is shown in table 2 Of the deep materials clean thickness pads of Filterdown 50 ordinarily retained 98.5 to 98.7 of freshly nebulized bacterial aerosols Impinger samples confirmed the 99 retention reported by Decker and his group for the same me: dium However one substandard lot was received which passed up to 15 of droplet nuclei This was returned to the manufacturer who confirmed the poor performance of the sample and stated that steps had been taken to prevent release of sub- standard lots in the future thickness pads of Aerosolve 95 a deep medium of considerably lower resistance to air flow than Filterdown FG showed an average retention of 95 with a range from 89 to 98.5 in different runs Retention of droplet nuclei by laden filters was higher than by clean filters Both mediums retained essentially 100 of bacteria dust particles produced by the powder blower It is reasonable to assume that any medium retaining 90 or more of an aerosol of droplet nuclei would retain essentially 100 of bacteria attached to atmospheric dust particles Unlike absolute filters deep filters are not individually guaranteed as to their efficiency by the manufacturer This fact suggests the need for test- ing the performance of individual filters used in critical situations especially in view of the variation we have observed in different lots of deep material Penetration of the glass and asbestos papers by droplet nuclei was roughly in proportion to their DOP ratings The high retention of these mediums was achieved only at a resistance to air flow significantly greater than that offered by the deep mediums A cotton surgical face mask retained less than 20 of staphylococcic droplet nuclei Field Studies Because of abnormally high bacterial counts in the operating rooms a survey of the two operating suites was undertaken With use of titanium tetra- chloride as an indicator it was determined that air from the corridor was being drawn into each of the four eye operating rooms and exhausted through ceiling ports in the scrub rooms and anesthesia rooms When the doors to the corridor were closed a brisk flow of air under them into the operating rooms was apparent The air flow at either end of the main corridor of the operating suite was then tested and it was found that air was being drawn under and between the double doors which opened into the main stair well of the hospital at one end of the corridor and into the ear nose and throat outpatient clinic at the other A similar situation was encountered in the ear nose and throat operating suite on the floor above A survey by ventilating engineers confirmed these findings It was brought out that the supply fans had been slowed in order to reduce the intake of outdoor dust through viscous panel filters At the same time exhaust fans in the anterooms continued to operate at their original speed so that a negative air pressure was created in the operating rooms The parallel between this situation and that re- ported by Blowers and workers is striking In accordance with the consultants recommenda- tions the exhaust ports were sealed off and fan speeds increased to the maximum 1,700 revolutions per minute creating a positive pressure in the oper- ating rooms Air escaped by exfiltration under doors and through louvers into surrounding areas The total air flow thus provided was between 500 and 600 cu ft per minute for each operating room with 100 outside air providing about 12 air changes per hour Viscous filter panels in the intake ducts TABLE Performance of New Filters to Operating Rooms Against Nebulized Staphylococcifi Room Colonies per Cu Ft a y Efficiency Upstrena Downstream % 1 e cece es crepe een cn tteesceeeecees ba 5.40 X 160 97 170 95 4 ... pas 97 * Pressure drop 0.24 water gauge 15min trials at 2 liters per minute for outside air were supplemented by banks of deep glass filters Acrosolve 95 in the distribution ducts to each operating room In order to test the efficiency of the completed installations samples were taken from the ducts at suitable locations upstream and downstream from the banks of filters while freshly nebulized and dry dust aerosols were being introduced through open- ings in the duct wall into the air stream from the supply air fan The first tests showed penetration of the order of 50 The fault was traced to defective installation and token calking of the cadmiumplated filter frames in the ducts and to omission of the rods used to seat the filter cartridges firmly against the felt gaskets in the frame This omission was contrary to the manufacturer's specifications In one instance the tapping screws used to fas- ten the water gauge manometer to the duet wall had forced the filter frame inward away from the duct After correction of these deficiencies reten- tion of the order of 95 was found for droplet nuclei table 3 The effect of ventilation on the concentration of droplet nuclei Staph albus nebulized into an operating room is shown in figure 2 76/266 AIR HYGIENE J.A.M.A. May 16 1959 Comment of Selection of a filter for a given purpose represents a compromise between high efficiency and low pressure drop inversely reflecting power cost and serv- ice life For air supplied to hospital operating rooms delivery rooms and nurseries this compro- mise must be resolved in terms the expected microbiological and particulate challenge to the filter and the efficiency of cleaning required of the filter against the expected challenge The state of bacteria and molds in outside atmos- pheric air is not entirely clear Colebrook and " Cawston found a preponderance of nonpatho- genic bacteria and molds with occasional colonies Log 2.0 _~ 1.8 Temperature 24C Relative humidity 34 samples samples .6 samples samples air |e in bacteria bacteria semiabsolute mediums would make their use appear uneconomical for air supplied to spaces in which human beings are continuously liberating organisms from their persons loosely No filter medium can be better than the of its installation As air seeks the path toifghtlneeassst resistance the volume of air bypassing a installed filter bank will increase with the of dust in the filter bed At the same tibmueillodw manometer readings may give the erroneous sion that the filter bed is operating well beilmopwreist-s maximum the permissible pressure drop when actually reverse is the case Unlike a plumbing installation a faulty air filter assembly shows no immediate sign of leakage Be- cause the load of particles entering the air intake during any short period of time is small dust and bacteria may accumulate before spilling over into a channel If alternate moisture and drying exist at an upstream location bacteria which have proliferated during the moist phase may strike the filter face en masse during the dry phase Detection of leakage would thus depend on prolonged sampling fortuitous sampling during a period of spillage or performance tests using a standard challenge of dust or bacteria bacteria 1.2 bacteria of concentration tol concentration concentration concentration concentration concentration 0.8 concentration initial initial 0.6 of of cent cent ^ per LOO10 LOO10 0.2 LOO10 0 Humidified molecular membrane sample Xx Electrostatic precipitalian sample 5 10 151 201 25 minutes | Fig Rate of disappearance of Staphylococcus albus from ventilated and unventilated rooms of Staph aureus in air sampled on the roof of their hospital There was no way of telling whether these organisms were floating or attached to dust particles The infrequency of the common human respiratory pathogens in their samples suggested that few bacteria existing as droplet nuclei survive drying and exposure to atmospheric conditions out of doors The efficiency of the deep mediums Filterdown FG and Aerosolve 95 together with a high rate of flow at a low pressure drop across the filters renders them acceptable for filtration of ordinary atmospheric air supplied to critical hospital areas The high pressure drop across the absolute and Neither the contractor nor the consulting engi neer carried out a performance test of the filters installed in the ducts leading to our operating rooms Moreover the consultant failed to detect the contractor's failure to meet the manufacturer's floor specifications for installing the filters No hospital should accept an installation which has not been found to retain at least 85 of atmospheric dust or its equivalent Ventilating engineers should be pre- pared to certify the initial performance of any high- efficiency filter system and to check any sam- ple of fibrous medium for substandard efficiency A correctly installed bank of deep glass filters protected by suitable viscous or electronic prefilters requires remarkably little maintenance After six months of continuous hour operation the pressure drop across the filters for our operating rooms had risen from 0.25 to 0.42 in of water maxi- mum allowable dirty drop is 0.8 in of water Other advantages include disposability ease of replace- ment and retention of dust during filter changes Heavy particles on the duct should be re- moved by vacuum cleaning at the time of filter changes The ceramic paper is intended for temper- ature dust filtration and would not normally find an application in hospital ventilating systems The absolute mediums because of their higher resistance to flow are not ordinarily used in air supply systems for hospitals The asbestos paper Micretain is stated by the manufacturer to be suitable for use in supply systems to operating rooms A cartridge presents 200 sq ft of pleated filtering surface and permits an Vol 170 No. 3 AIR HYGIENE air flow of 1,000 cu ft per minute at a clean rated pressure drop of 0.4 in water gauge Because of its higher efficiency greater uniformity and longer service life 4,000 hours with adequate prefiltration the manufacturer believes that this will be an eco- 77/267 ticles and high retention of bacterial droplet nuclei A asbestos paper intended for offered retention in the same range hospital use 200 Beacon St. 16 nomical filter for critical hospital air supply situ- ations The excellent retention rate of several fibrous filters suggests the desirability of designing ventilating systems to permit partial recirculation of air The advantages of recirculation in permitting easier and cheaper control of temperature and humidity are obvious especially where explosive vapors are not in use Even when volatile agents are being ^"sedThomas " feels that the present requirement of 100 outside air is unreasonable and that 50 recirculation would be perfectly safe at the same relative humidity In ordinary ventilating situations the need to sterilize fibrous filters in place does not arise If it became necessary to sterilize a heavily contami- nated exhaust filter this could be done with beta- propiolactone in the vapor phase 16 or with ethylene oxide in suitable combination with an inert gas The high efficiency of Filterdown FG permits other applications in the field of air filtration At the suggestion of Snow this material has been em- ployed as a tertiary filter in an industrial vacuum cleaner Kent Quiet Junior which is suitable for use in hospitals At a volume output of 135 cu ft per minute and at an air velocity of 210 ft per min ute through the medium a thickness pad of Filterdown FG placed upstream from the twin motor intakes retained 99.8 of nebulized staphylococci either alone or in conjunction with the normal primary paper bag and secondary cloth bag filters of the machines The higher efficiency observed at the higher velocity is consistent with arrest by inertial impaction The low resistance to air flow of Aerosolve 95 and 85 suggests a possible application in surgical masks We are currently exploring the use of these materials as a better means of checking bacteria of respiratory tract origin at their source This study was supported in part by the Massachusetts Eye and Ear Infirmary through its Bacteriology Research Fund Mr. Werner Mueller Jr. supplied parts of the mechanical equipment and Mr. David Feigenbaum supplied figure 1 References 1. Fredette .: Bacteriological Efficiency of Condi- tioning Systems in Operating Rooms Canad J. Surg 226- 229 April 1958 i 2. Bourdillon R. .: Practical Advantages of Different Methods of Air Disinfection in Studies in Air Hygiene Medical Research Council Special Report Series No. 262 London His Majesty's Stationery Office 1948 pp 311-318 3. Wells W. .: Airborne Contagion and Air Hygiene Ecological Study of Droplet Infections Cambridge Harvard University Press 1955 p 9 4. Phelps E. B State of Suspension of Bacteria in Air as Measured by Settling Rates in Aerobiology edited by F. R. Moulton American Association for the Advancement of Sci- ence publication no 17 1942 p 136 5. Wells p 44 6. Friedlander S. K Silverman L Drinker P and First M. W Handbook of Air Cleaning Washington D. C. U. S. Atomic Energy Commission 1952 7. a Decker H. M Geile F. A Moorman H. E and Glick C. A Removal of Bacteria and Bacteriophage from Air by Electrostatic Precipitation and Spun Glass Filter Pads Heating Piping & Air Conditioning Am Soc Heating & Ventilating Engineers J. 125 Oct. 1951. b Lidwell O. M Bacterial Filtration Efficiency of Electrostatic Air Cleaner J. Inst Heating & Ventilating Engineers 139 1951 8. Decker H. M Harsted J. B Piper F. .; and Wilson M. E Filtration of Microorganisms from Air by Class Fiber Media Heating Piping & Air Conditioning Am Soc Heat- ing & Ventilating Engineers J. 155 May 1954. Refer- ence 7a 9. Rosebury T Experimental Borne Infection Baltimore Williams & Wilkins Company 1947 pp 90-92 Ferry R. M Brown W. F and Damon E. Studies of Viability of Stored Bacterial Aerosols Death Rates Loss of of Sev eral Pathogenic Organisms in Relation to Biological and Structural Characteristics J. Hyg 125-150 March 1958 10. Cown W. B Kethley T. W and Fincher E. 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C Microbic Con- Council tent of Air on Roof of City Hospital at Street Level and in Wards in Studies in Air Hygiene Medical Research Special Report Series No. 262 London His Majesty's Stationery Office 1948 pp 233 241 15. Thomas C. .: Air Conditioning in Hospitals Anesth & Analg 32-35 Jan. 1957 between it and the space being ventilated is essential Two deep glass materials were found to provide absolute filtration of bacteria on dust par- 16. Hoffman tone Vapor as Sept. 1958 17. Snow D. R. K. and Warshowsky .: Propiolac- Disinfectant Appl Microbiol 358-362 L Unpublished data