A problem of hospital hygiene: The presence of aspergilli in hospital wards with different air-conditioning features
A problem of hospital hygiene: The presence of aspergilli in hospital wards with different air-conditioning features
Fernanda Perdelli, BScD, PhD,a Marina Sartini, BScD, PhD,a Anna Maria Spagnolo, BScD,a Maurizio Dallera, BScD,a Roberto Lombardi, BScD, PhD,b and Maria Luisa Cristina, BScD, PhDa Geneva and Rome, Italy
A total of 1030 microbiological samples were taken in 3 hospital wards with different air-conditioning features: no conditioning system (ward A), a conditioning system equipped with minimum efficiency reporting value (MERV) filters (ward B), and a condi tioning system thoroughly maintained and equipped with high-efficiency paniculate air (HEPA) filters (absolute) (ward C). The air in each ward was sampled, and the bacterial and fungal concentrations were determined by active and passive methods. The con centration of fungi on surfaces was also determined. Active sampling showed positive samples in wards A and Β only, with average values of 0.50 colony-forming units (CFU)/m3 (95 % CI, 0.30 to 0.70) in A and 0.16 CFU/m3 (95 % CI, 0.13 to 0.20) in B. Passive sam pling was positive only in ward A (mean, 0.14 CFU/cm2/h; 95% CI, 0.13 to 0.15). Aspergillus was found in 27% and 22% of sampled surfaces in wards A and B, respectively, but in no samples from ward C. The most commonly found species was A.fumigatus (76% of cases in A and 34% of cases in B). The results show that the use of air-conditioning systems markedly reduces the concentration of aspergilli in the environment. Proper maintenance of these systems is clearly fundamental if their efficacy is to be ensured. (Am J Infect Control 2006:34:264-8.)
Invasive aspergillosis is one of the most lethal forms in immunosuppressed subjects, even if it is treated. The main form of hospital infection caused by asper gilli is pulmonitis. The infection may, however, spread through the bloodstream to other organs, particularly the brain, but also the eye, the heart, the kidney, and the skin1'3; in such cases, the condition is more serious and mortality increases (http://www.aspergillus.man.ac.uk).
The percentage of cases of invasive aspergillosis must be assessed according to separate patient cate gories; such infections mainly involve patients affected by chronic granulomatous diseases (25% to 40%), fol lowed in descending order by lung or heart-lung trans plant patients (19% to 26%), those suffering from acute leukemia (5% to 24%), and allogenic bone-marrow recipients (4% to 9%). With regard to autolo-gous transplant recipients; acquired immunodeficiency syndrome patients; liver, heart, and kidney transplant recipients; patients affected by severe combined immu nodeficiency; burn patients; and subjects affected by
systemic lupus erythematosus; the percentage of aspergillosis varies from a minimum of 0.5 % to a max imum of 10%.4'6
The percentage range of aspergillosis reported in the literature may be broad because the state of immuno deficiency of the patients, which is a basic determinant of fungal colonization, may vary markedly. In the last 20 years, cases of invasive aspergillosis corroborated by autopsy findings have increased from 0.4% to 4% ,7·8 This increase is partly attributable to the greater number of patients with critical illnesses who survive for a longer period as a result of advances in medical technology. Further causes of this increase can be seen in the advent of AIDS, the development of inten sive chemotherapy protocols for the treatment of solid tumors; difficult lymphomas, myelomas, and resistant forms of leukemia; the growing number of organ trans plantations; and finally, the widespread use of im-munosuppressive therapies for autoimmune diseases, such as lupus erythematosus and so on.8
Invasive aspergillosis may have very severe conse quences; mortality rates are high and vary according to the patient populations examined, reaching 95% in allogenic transplant recipients and in patients af fected by aplastic leukemia, and ranging from 13 % to 80% in leukemia patients according to the Centers for Disease Control and Prevention.9
With a view to assessing the impact of the technical and maintenance features of ventilation and air-con ditioning systems on the level of pollution by aspergilli in hospital wards, we measured the concentration of fungi in the air and on surfaces in various hospital wards for immunosuppressed patients, in which envi ronmental contamination must be controlled.
METHODS
Three hospital wards for patients at risk were cho sen: a 3-bed bone-marrow transplantation unit for pa tients with high-grade immunodepression (ward A), a 12-bed intensive-care and subintensive-care unit for patients with variable-grade immunodepression (ward B), and a ΙΟ-bed ward for patients with infectious diseases (mainly meningitis, hepatitis, and human im munodeficiency virus infection) and cancer patients with variable-grade immunodepression (ward C).
The 3 wards are all located in different buildings: ward A is situated on the sixth floor of a building con structed in the 1960s, ward Β is located on the ground floor of a 1980s building, and ward C (modernized in the 1990s) is on the second floor of a building dating from the 1950s. None of these buildings, as a whole, has suffered episodes of contamination in the past; only ward Β has suffered from infiltration by water.
The wards were similar from the organizational point of view (the staff of each followed virtually the same organizational-behavioral protocols to keep envi ronmental contamination under control).
The first ward (ward A) had no air-conditioning system. The second (ward B) had an air-condition ing system that was equipped with filters with 80% to 85 % efficiency (minimum efficiency reporting value [MERV] 11 to 12) and was rather poorly maintained (eg, filters were not replaced or regenerated regularly, nor was there a specific cleaning protocol); although this system ensured that the air pressure inside the ward was higher than that of the surrounding environ ments, the numerical value of the inside pressure was not provided by the technical office responsible. The third (ward C) had a scrupulously maintained system equipped with high-efficiency particulate air (HEPA) filters, efficiency >99.97% (absolute); this system lowered the internal pressure by 1 Pa. With regard to maintenance, every 6 months the air handling units were cleaned, descaled (if necessary) and sanitized by means of special detergents and solutions, and the fil ters were changed. In wards B and C, the air-condition ing systems were equipped with turbulent airflow and provided 6 exchanges per hour.
In each ward, air samples were taken and the airborne and sedimenting mycotic loads were deter mined. The fungal concentration on surfaces was also determined. All active and passive sampling was car ried out in the center of the rooms examined.
In addition, the total airborne bacterial load was also evaluated as a global index of the quality of the air. The mycotic load was measured using Sabouraud culture
medium with chloramphenicol (Biotest Heipha Diag-nostika, Heidelberg, Germany), and the total bacterial load was determined using the plate count agar (Biotest Heipha Diagnostika).
For active bacterial and mycotic sampling, we used an SAS (Surface Air System) impactor (FBI Interna tional, Milan, Italy) equipped with plates containing culture media; the volume of air aspirated for each sample was si m3.10 Serial samples were taken within the space of 1 hour on the same plate to enable com parisons to be made with passive sampling of the same duration.
In each ward, at least 3 samples were taken by means of SAS and 3 by means of exposed plates for the determination of both total bacterial load and my cotic load. In this latter case, at least 10 determinations of the sedimented load were carried out. In all, 1030 de terminations were carried out, samples were taken in the same season (springtime), and in each ward, each series of samples was performed on the same date.
The mycotic and sedimenting bacterial loads were measured by exposing 5-cm diameter Petri plates to the ambient air for 1 hour; the plates were positioned 1 m from the nearest wall and at a height of 1 m from the floor. Finally, with regard to the sedimented mycotic load, sampling was carried out in the vicinity of the patients' beds, if possible on horizontal surfaces, near electrical equipment and near inlet and outlet air ducts where present. Because the surfaces were irregu lar, samples were taken by means of swabs; each sam ple covered a total area of 100 cm2, and the yield was seeded onto a selective culture medium.
After sampling, the Sabouraud plates were placed in a thermostat and incubated for 5 days at 25°C to enable the fungi to develop, and the plate count agar (PCA) plates for 2 days at 37°C to assess the total bacterial load. The number of colonies was then expressed as CFU/m3 for the bacterial and the airborne mycotic load, as CFU/cm2/h for the sedimenting mycotic load, and as CFLJ/dm2 for surfaces.
The fungal colonies obtained by means of the 3 methods described above were identified by macro scopic and microscopic analyses.
RESULTS
Table 1 reports the mean values and the 95 % con fidence intervals of the total bacterial load (airborne and sedimenting) and the mycotic load (airborne, sedi menting, and sedimented) in the 3 wards examined.
The mean concentrations of the total bacterial load (Table 1) measured by means of active sampling were: 265 CFU/m3 (95% CI, 260 to 270) in the ward without air-conditioning (A); 130 CFU/m3 (95% CI, 126 to 134) in the ward with an air-conditioning system
Table I. Number of samples, mean values, and confidence intervals with regard to the airborne and sedimenting bacterial and fungal load and the fungal load measured on surfaces in wards with different air-conditioning systems
Active sampling (CFU/m3) Passive sampling (CFU/cm2/h) Surface sampling (CFU/dm2)
Ν Mean 95% Cl Ν Mean 95% Cl Ν Mean 95% Cl
A, ward without an air-conditioning system; β, ward with an air-conditioning system without absolute filters; C, ward with an air-conditioning system equipped with absolute HEPA filters.
CPU, colony-form ing units; HEPA, high-efficiency paniculate air.
without HEPA (absolute) filters (B), and 20 CFU/m3 (95% Cl, 18 to 22) in the ward equipped with HEPA (absolute) filters (C). Passive sampling of the bacterial load showed mean values of 0.70 CFU/cm2/h (95% Cl, 0.35 to 0.80) in ward A, 0.26 CFU/cm2/h (95% Cl, 0.20 to 0.40) in ward B, and 0.019 CFU/cm2/h (95% Cl, 0.01 to 0.023) in ward C.
With regard to the mycotic load (Table 1), active sampling showed positive samples only in wards A and B, with mean values of 0.50 CFU/m3 (95% Cl, 0.30 to 0.70) and 0.16 CFU/m3 (95% Cl, 0.13 to 0.20), respectively. Passive sampling showed the presence of fungi only in ward A, with a mean value of 0.14 CFU/cm2/h (95% Cl, 0.13 to 0.15).
The mean values yielded by surface sampling were 0.51 CFU/dm2 (95% Cl, 0.46 to 0.55) and 0.22 CPU/ dm2 (95% Cl, 0.15 to 0.29) in wards A and B, respec tively; no positive samples were found in ward C.
In ward A, 14 active samples (30%), 8 passive sam ples (16%), and 48 surface samples (27%) proved pos itive for Aspergillus; in ward B, Aspergillus was found in 8 active samples (16%) and 35 surface samples (22%), whereas no passive sample proved positive (Table 2).
The colonies of Aspergillus sampled were sub sequently isolated and identified. In ward A, 76% of cases proved to be constituted by A. fumigatus, 12% by A. niger, and the remaining 12 % by A. flavus; in ward B, 66% were A. niger and 34% were A. fumigatus.
The fungal species in the wards examined were dis tributed as follows: in ward A, 72.2 % of all A. fumigatus, 50% of all A. niger, and 62.5% of all A. flavus detected was found on surfaces; in ward B, 66.6 % of all A. fumi gatus and 89.3 % of all A. niger was found on surfaces.
DISCUSSION
The choice of the 3 different situations was promp ted by the fact that in Italy many hospital wards for
Table 2. Number of colonies of Aspergillus spp (N) and percentage of positive samples found in each ward
A B C
---------- ----------- ----------
Ν % Ν % Ν %
A, ward without an air-conditioning system; B, ward with an air-conditioning system without absolute filters; C, ward with an air-conditioning system equipped with absolute HEPA filters. CPU, colony-forming units; HEPA, high-efficiency particulate air.
high-risk patients still have no air-conditioning systems, or else are equipped with systems that do not use HEPA (absolute) filters.
In our study, the ward with no air-conditioning sys tem (A) obviously had the worst results on all 3 types of sampling carried out; the total bacterial load and the sedimented mycotic load were almost twice as high as the values recorded in the ward with the system without HEPA (absolute) filters (B). This pattern was also seen in the percentage of samples positive for air borne Aspergillus, which was again twice as high in A as in B. With regard to surface sampling, the results show a nonnegligible presence of Aspergillus, both in terms of mean values and in terms of the percentage frequency of positive samples. Moreover, it should be borne in mind that the surface sampling procedure, al beit standardized, underestimates the numerical values of the fungi present. This is attributable to several rea sons; not all microorganisms are detached from the surface during sampling; some microorganisms will not be transferred from the swab to the culture me dium; and finally, the stress suffered by all microorgan isms, including fungi, during the sampling procedure affects their capacity for growth and therefore influ ences the final colony count. Because fungi can remain viable in the environment for long periods, surfaces constitute a much better reservoir of contamination for them than for bacteria. Thus, determining the con centration of fungi on surfaces is a meaningful way of assessing potential risk. For this reason, we only mea sured the sedimented load of fungi and not that of bacteria.
In light of what has been said, it is highly likely that the number of aspergilli actually present is greater. In terms of health risks, what is much more serious is the fact that the species identified were those (A. fumi-gatus and A. flavus) most frequently involved in cases of hospital aspergillosis.
From the epidemiologic standpoint, there is no sci entific proof that systematic vigilance against contam ination by fungi in at-risk hospital environments is effective.11 By contrast, environmental testing for the presence of fungi is meaningful if it is seen as a means of ensuring that air-conditioning systems and the be havior and organization of hospital staff are kept up to the desired standard.
Environmental sampling is an important method of checking the coherent application of all those prophy lactic procedures that should be implemented to ward off aspergillosis. It is therefore an expression of the environmental quality attained; such quality is influ enced by numerous factors, such as the behavior of the personnel, how the department is run, the charac teristics of the building and its installations, etc.
Clearly, departments equipped with air-conditioning systems that use HEPA (absolute) filters and in which the goal is to eliminate aspergilli entirely should install a monitoring system to check the overall quality attained.
Concerning the presence of fungi, surveillance pro cedures in protected environments are not currently standardized regarding the practical aspects, the meth ods of analysis, or the interpretation of results.11
Regarding health risks, it should nevertheless be emphasized that environmental sampling is a funda mental step in checking and controlling contamination by Aspergillus. Because the 3 sampling methods have different implications for health risks, they should be used simultaneously and the results that emerge should be evaluated together to assess the health risk accurately.
Active sampling, which measures the airborne mycotic load, expresses the direct risk of inhalation, whereas passive sampling, which reveals the sedi-menting load, expresses the indirect risk of inhalation; finally the sedimented load, that is to say the fungi adhering to deposited dust, indicates the potential risk. Indeed, the sedimented load is an indicator of the size of the reservoir from which the aspergilli can re-enter the environment; as a result of their
physical-chemical and aerodynamic features, spores that settle can develop in a short time and become airborne again by means of chance movements of the air caused by patients themselves, staff, or air-convection streams. Sedimented fungi are therefore able to re-contaminate the environment and to come into contact with patients again. Thus, the results of surface sampling seem to be the most significant in assessing the potential risk to which the patient is exposed. In this regard there is no consensus on the conidial density at which the risk of invasive aspergil losis (IA) is increased. Rhame12 reported a higher risk of IA when the average density of A. fumigatus was 0.9 CFU/m3. Arnow et al13 noted a marked decrease in the incidence of IA when Aspergillus density de creased from 1 to 2 to <0.2 CFU/m3. Sheretz et al2 reported no cases of IA after conidial density was reduced to 0.009 CFU/m3. Using a regression model, Al-berti et al14 found a significant relationship between the incidence of invasive nosocomial aspergillosis (ΙΝΑ) and the degree of fungal contamination of air and surfaces in conventional patient rooms (not equip ped with HEPA (absolute) filters) and common sites. In particular, they showed that peaks of air contamination by Aspergillus >2 CFU/m3 had a determining role in the relationship between environmental contamina tion and the occurrence of IA.
The results of the present study show that the use of air-conditioning systems can considerably reduce the concentration of aspergilli in the environment. Such systems cannot, however, eliminate the risk of con tamination unless they are scrupulously maintained and, at the same time, all the norms for environ mental prophylaxis indicated in the literature are respected.6·10·13·15-18
As amply reported by other investigators,9·11·15 the use of air-conditioning systems equipped with HEPA (absolute) niters is to be recommended in wards where there are patients with a level of polynucleate neutrophils below 500/mm3 persisting for 2 weeks or longer, or less than 100/mm3 whatever the duration of neutropenia.
It is practically impossible to eliminate the risk of aspergillosis entirely, but it can be reduced to a mini mum. Indeed, the use of an appropriate air-condition ing system (equipped with HEPA absolute filters), proper maintenance of the system itself, the applica tion of protocols for sanitization and staff behavior recommended for critical wards, etc, contribute to reducing the risk of aspergillosis significantly.
The need to do so is dictated, in the first place, by ethical considerations, in that the patient must be safe guarded, and in the second place by professional and economic considerations, in that the therapeutic ef forts undertaken should not be thwarted.
References
1. Fridkin SK, Jarvis WR. Epidemiology of nosocomial fungal infections. Clin Microbiol Rev I996;9:499-SI I.
2. Sherertz RJ, Belani A, Kramer BS, Elfenbein GJ, Weiner RS, Sullivan ML, et al. Impact of air filtration on nosocomial Aspergillus infections. Unique risk of bone marrow transplant recipients. Am J Med 1987;83: 709-18.
3. Young RC, Bennet JE, Vogel CL, Carbone PR De Vita VT. Aspergillosis: spectrum of the disease in 98 patients. Medicine 1970:49:147-73.
4. Denning DW. Invasive aspergillosis. Clin Infect Dis 1998:26:781-805.
5. Manuel RJ, Kibbler CC. The epidemiology and prevention of invasive aspergillosis. J Hosp Infect 1998:39:95-109.
6. Walsh TJ, Dixon DM. Nosocomial aspergillosis: environmental micro biology, hospital epidemiology, diagnosis and treatment. Eur J Epide-miol 1989:5:131-42.
7. Groll AH, Shah PM, Mentzel C, Scheider M, Just-Nuebling G, Huebner K. Trends in the postmortem epidemiology of invasive fungal infec tions at a university hospital. J Infect 1996:33:23-32.
8. Yamazaki T, Kume H, Murase S, Yamashita E, Arisawa M. Epidemiology of visceral mycoses: analysis of data in annual of the pathological autopsy cases in Japan. J Clin Microbiol 1999:37:1732-8.
9. CDC Guidelines for Prevention of Nosocomial Pneumonia. MMWR Morb Mortal Wkly Rep 1997:46:1-79.
10. Morey PR. Guidelines for assessment and sampling of saprophytic bioaerosols in the indoor environment. Appl Ind Hyg !987;2:RIO-6.
11. Leporrier M, Bastides F, Botti P, Bordessoule D, Caubarre I, Cetre JC, et al. Prevention du risque aspergillaire chez les patients immunode-primes. In: Texte des recommandations. Conference de Consensus ANAES, Paris 2000.
12. Rhame FS. Prevention of nosocomial aspergillosis. J Hosp Infect 1991; 18:466-72.
13. Arnow PM, Sadigh M, Costas C, Weil D, Chudy R. Endemic and epi demic aspergillosis associated with in-hospital replication of Asperg/Mus organisms. J Infect Dis 1991; 164:998-1002.
14. Alberti C, Bouakline A, Ribaud P, Lacroix C, Rousselot P, Leblanc T, et al. Aspergillus Study Group:Relationship between environmental fungal contamination and the incidence of invasive aspergillosis in haema-tology patients. J Hosp Infect 2001 ;48:198-206.
15. CDC guidelines for preventing opportunistic infections among hema-topoietic stem cell. MMWR Morb Mortal Wkly Rep 2000;49:1 -128.
16. Kennedy HF, Michie JR, Richardson MD. Air sampling for Aspergillus spp during building activity in paediatric hospital ward. J Hosp Infect 1995:31:322-5.
17. Krasinski K, Holzman RS, Hanna B, Greco MA, Graff M, Bhogal M. Nosocomial fungal infection during hospital renovation. Infect Control 1985:6:278-82.
18. Weems JJ Jr, Davis BJ, Tablan OC, Kaufman L, Martone WJ. Construc tion activity: an independent risk factor for invasive aspergillosis and zygomycosis in patients with hematologic malignancy. Infect Control 1987:8:71-5.
Fernanda Perdelli, BScD, PhD,a Marina Sartini, BScD, PhD,a Anna Maria Spagnolo, BScD,a Maurizio Dallera, BScD,a Roberto Lombardi, BScD, PhD,b and Maria Luisa Cristina, BScD, PhDa Geneva and Rome, Italy
A total of 1030 microbiological samples were taken in 3 hospital wards with different air-conditioning features: no conditioning system (ward A), a conditioning system equipped with minimum efficiency reporting value (MERV) filters (ward B), and a condi tioning system thoroughly maintained and equipped with high-efficiency paniculate air (HEPA) filters (absolute) (ward C). The air in each ward was sampled, and the bacterial and fungal concentrations were determined by active and passive methods. The con centration of fungi on surfaces was also determined. Active sampling showed positive samples in wards A and Β only, with average values of 0.50 colony-forming units (CFU)/m3 (95 % CI, 0.30 to 0.70) in A and 0.16 CFU/m3 (95 % CI, 0.13 to 0.20) in B. Passive sam pling was positive only in ward A (mean, 0.14 CFU/cm2/h; 95% CI, 0.13 to 0.15). Aspergillus was found in 27% and 22% of sampled surfaces in wards A and B, respectively, but in no samples from ward C. The most commonly found species was A.fumigatus (76% of cases in A and 34% of cases in B). The results show that the use of air-conditioning systems markedly reduces the concentration of aspergilli in the environment. Proper maintenance of these systems is clearly fundamental if their efficacy is to be ensured. (Am J Infect Control 2006:34:264-8.)
Invasive aspergillosis is one of the most lethal forms in immunosuppressed subjects, even if it is treated. The main form of hospital infection caused by asper gilli is pulmonitis. The infection may, however, spread through the bloodstream to other organs, particularly the brain, but also the eye, the heart, the kidney, and the skin1'3; in such cases, the condition is more serious and mortality increases (http://www.aspergillus.man.ac.uk).
The percentage of cases of invasive aspergillosis must be assessed according to separate patient cate gories; such infections mainly involve patients affected by chronic granulomatous diseases (25% to 40%), fol lowed in descending order by lung or heart-lung trans plant patients (19% to 26%), those suffering from acute leukemia (5% to 24%), and allogenic bone-marrow recipients (4% to 9%). With regard to autolo-gous transplant recipients; acquired immunodeficiency syndrome patients; liver, heart, and kidney transplant recipients; patients affected by severe combined immu nodeficiency; burn patients; and subjects affected by
From the DISSAL, Sez. Igiene e Medicina Preventiva, Universita degli Studi di Geneva, Genova, Italy,3 and ISPESL, Dipartimento Igiene del Lavoro, V. Fontana Candida I, Monteporzio Catone, Roma.b Reprint requests: Maria Luisa Cristina, BScO, PhD, Department of Health Sciences, University of Genoa, Via Pastore, 1-16132 Genova, Italy. E-mail: [email protected]. 0I96-6553/$32.00 Copyright © 2006 by the Association for Professionals in Infection Control and Epidemiology, Inc. |
systemic lupus erythematosus; the percentage of aspergillosis varies from a minimum of 0.5 % to a max imum of 10%.4'6
The percentage range of aspergillosis reported in the literature may be broad because the state of immuno deficiency of the patients, which is a basic determinant of fungal colonization, may vary markedly. In the last 20 years, cases of invasive aspergillosis corroborated by autopsy findings have increased from 0.4% to 4% ,7·8 This increase is partly attributable to the greater number of patients with critical illnesses who survive for a longer period as a result of advances in medical technology. Further causes of this increase can be seen in the advent of AIDS, the development of inten sive chemotherapy protocols for the treatment of solid tumors; difficult lymphomas, myelomas, and resistant forms of leukemia; the growing number of organ trans plantations; and finally, the widespread use of im-munosuppressive therapies for autoimmune diseases, such as lupus erythematosus and so on.8
Invasive aspergillosis may have very severe conse quences; mortality rates are high and vary according to the patient populations examined, reaching 95% in allogenic transplant recipients and in patients af fected by aplastic leukemia, and ranging from 13 % to 80% in leukemia patients according to the Centers for Disease Control and Prevention.9
With a view to assessing the impact of the technical and maintenance features of ventilation and air-con ditioning systems on the level of pollution by aspergilli in hospital wards, we measured the concentration of fungi in the air and on surfaces in various hospital wards for immunosuppressed patients, in which envi ronmental contamination must be controlled.
METHODS
Three hospital wards for patients at risk were cho sen: a 3-bed bone-marrow transplantation unit for pa tients with high-grade immunodepression (ward A), a 12-bed intensive-care and subintensive-care unit for patients with variable-grade immunodepression (ward B), and a ΙΟ-bed ward for patients with infectious diseases (mainly meningitis, hepatitis, and human im munodeficiency virus infection) and cancer patients with variable-grade immunodepression (ward C).
The 3 wards are all located in different buildings: ward A is situated on the sixth floor of a building con structed in the 1960s, ward Β is located on the ground floor of a 1980s building, and ward C (modernized in the 1990s) is on the second floor of a building dating from the 1950s. None of these buildings, as a whole, has suffered episodes of contamination in the past; only ward Β has suffered from infiltration by water.
The wards were similar from the organizational point of view (the staff of each followed virtually the same organizational-behavioral protocols to keep envi ronmental contamination under control).
The first ward (ward A) had no air-conditioning system. The second (ward B) had an air-condition ing system that was equipped with filters with 80% to 85 % efficiency (minimum efficiency reporting value [MERV] 11 to 12) and was rather poorly maintained (eg, filters were not replaced or regenerated regularly, nor was there a specific cleaning protocol); although this system ensured that the air pressure inside the ward was higher than that of the surrounding environ ments, the numerical value of the inside pressure was not provided by the technical office responsible. The third (ward C) had a scrupulously maintained system equipped with high-efficiency particulate air (HEPA) filters, efficiency >99.97% (absolute); this system lowered the internal pressure by 1 Pa. With regard to maintenance, every 6 months the air handling units were cleaned, descaled (if necessary) and sanitized by means of special detergents and solutions, and the fil ters were changed. In wards B and C, the air-condition ing systems were equipped with turbulent airflow and provided 6 exchanges per hour.
In each ward, air samples were taken and the airborne and sedimenting mycotic loads were deter mined. The fungal concentration on surfaces was also determined. All active and passive sampling was car ried out in the center of the rooms examined.
In addition, the total airborne bacterial load was also evaluated as a global index of the quality of the air. The mycotic load was measured using Sabouraud culture
medium with chloramphenicol (Biotest Heipha Diag-nostika, Heidelberg, Germany), and the total bacterial load was determined using the plate count agar (Biotest Heipha Diagnostika).
For active bacterial and mycotic sampling, we used an SAS (Surface Air System) impactor (FBI Interna tional, Milan, Italy) equipped with plates containing culture media; the volume of air aspirated for each sample was si m3.10 Serial samples were taken within the space of 1 hour on the same plate to enable com parisons to be made with passive sampling of the same duration.
In each ward, at least 3 samples were taken by means of SAS and 3 by means of exposed plates for the determination of both total bacterial load and my cotic load. In this latter case, at least 10 determinations of the sedimented load were carried out. In all, 1030 de terminations were carried out, samples were taken in the same season (springtime), and in each ward, each series of samples was performed on the same date.
The mycotic and sedimenting bacterial loads were measured by exposing 5-cm diameter Petri plates to the ambient air for 1 hour; the plates were positioned 1 m from the nearest wall and at a height of 1 m from the floor. Finally, with regard to the sedimented mycotic load, sampling was carried out in the vicinity of the patients' beds, if possible on horizontal surfaces, near electrical equipment and near inlet and outlet air ducts where present. Because the surfaces were irregu lar, samples were taken by means of swabs; each sam ple covered a total area of 100 cm2, and the yield was seeded onto a selective culture medium.
After sampling, the Sabouraud plates were placed in a thermostat and incubated for 5 days at 25°C to enable the fungi to develop, and the plate count agar (PCA) plates for 2 days at 37°C to assess the total bacterial load. The number of colonies was then expressed as CFU/m3 for the bacterial and the airborne mycotic load, as CFU/cm2/h for the sedimenting mycotic load, and as CFLJ/dm2 for surfaces.
The fungal colonies obtained by means of the 3 methods described above were identified by macro scopic and microscopic analyses.
RESULTS
Table 1 reports the mean values and the 95 % con fidence intervals of the total bacterial load (airborne and sedimenting) and the mycotic load (airborne, sedi menting, and sedimented) in the 3 wards examined.
The mean concentrations of the total bacterial load (Table 1) measured by means of active sampling were: 265 CFU/m3 (95% CI, 260 to 270) in the ward without air-conditioning (A); 130 CFU/m3 (95% CI, 126 to 134) in the ward with an air-conditioning system
Table I. Number of samples, mean values, and confidence intervals with regard to the airborne and sedimenting bacterial and fungal load and the fungal load measured on surfaces in wards with different air-conditioning systems
Active sampling (CFU/m3) Passive sampling (CFU/cm2/h) Surface sampling (CFU/dm2)
Ν Mean 95% Cl Ν Mean 95% Cl Ν Mean 95% Cl
| A | |||||||||
| Bacteria | 48 | 265 | 260-270 | 48 | 0.70 | 0.35-0.80 | - | - | |
| Fungi | 48 | 0.50 | 0.30-0.70 | 48 | 0.14 | 0.13-0.15 | 178 | 0.51 0.46-0.55 | |
| Β | |||||||||
| Bacteria | 48 | 130 | 126-134 | 48 | 0.26 | 0.20-0.40 | - | - | |
| Fungi | 48 | 0.16 | 0.13-0.20 | 48 | 0 | - | 160 | 0.22 0.15-0.29 | |
| C | |||||||||
| Bacteria | 42 | 20 | 18-22 | 42 | 0.019 | 0.01-0.023 | - | - | |
| Fungi | 42 | 0 | - | 42 | 0 | - | 140 | 0 |
A, ward without an air-conditioning system; β, ward with an air-conditioning system without absolute filters; C, ward with an air-conditioning system equipped with absolute HEPA filters.
CPU, colony-form ing units; HEPA, high-efficiency paniculate air.
without HEPA (absolute) filters (B), and 20 CFU/m3 (95% Cl, 18 to 22) in the ward equipped with HEPA (absolute) filters (C). Passive sampling of the bacterial load showed mean values of 0.70 CFU/cm2/h (95% Cl, 0.35 to 0.80) in ward A, 0.26 CFU/cm2/h (95% Cl, 0.20 to 0.40) in ward B, and 0.019 CFU/cm2/h (95% Cl, 0.01 to 0.023) in ward C.
With regard to the mycotic load (Table 1), active sampling showed positive samples only in wards A and B, with mean values of 0.50 CFU/m3 (95% Cl, 0.30 to 0.70) and 0.16 CFU/m3 (95% Cl, 0.13 to 0.20), respectively. Passive sampling showed the presence of fungi only in ward A, with a mean value of 0.14 CFU/cm2/h (95% Cl, 0.13 to 0.15).
The mean values yielded by surface sampling were 0.51 CFU/dm2 (95% Cl, 0.46 to 0.55) and 0.22 CPU/ dm2 (95% Cl, 0.15 to 0.29) in wards A and B, respec tively; no positive samples were found in ward C.
In ward A, 14 active samples (30%), 8 passive sam ples (16%), and 48 surface samples (27%) proved pos itive for Aspergillus; in ward B, Aspergillus was found in 8 active samples (16%) and 35 surface samples (22%), whereas no passive sample proved positive (Table 2).
The colonies of Aspergillus sampled were sub sequently isolated and identified. In ward A, 76% of cases proved to be constituted by A. fumigatus, 12% by A. niger, and the remaining 12 % by A. flavus; in ward B, 66% were A. niger and 34% were A. fumigatus.
The fungal species in the wards examined were dis tributed as follows: in ward A, 72.2 % of all A. fumigatus, 50% of all A. niger, and 62.5% of all A. flavus detected was found on surfaces; in ward B, 66.6 % of all A. fumi gatus and 89.3 % of all A. niger was found on surfaces.
DISCUSSION
The choice of the 3 different situations was promp ted by the fact that in Italy many hospital wards for
Table 2. Number of colonies of Aspergillus spp (N) and percentage of positive samples found in each ward
A B C
---------- ----------- ----------
Ν % Ν % Ν %
| Active sampling | 14 | 30 | 8 | 16 | 0 | 0 |
| Passive sampling | 8 | 16 | 0 | 0 | 0 | 0 |
| Surface sampling | 48 | 27 | 35 | 22 | 0 | 0 |
A, ward without an air-conditioning system; B, ward with an air-conditioning system without absolute filters; C, ward with an air-conditioning system equipped with absolute HEPA filters. CPU, colony-forming units; HEPA, high-efficiency particulate air.
high-risk patients still have no air-conditioning systems, or else are equipped with systems that do not use HEPA (absolute) filters.
In our study, the ward with no air-conditioning sys tem (A) obviously had the worst results on all 3 types of sampling carried out; the total bacterial load and the sedimented mycotic load were almost twice as high as the values recorded in the ward with the system without HEPA (absolute) filters (B). This pattern was also seen in the percentage of samples positive for air borne Aspergillus, which was again twice as high in A as in B. With regard to surface sampling, the results show a nonnegligible presence of Aspergillus, both in terms of mean values and in terms of the percentage frequency of positive samples. Moreover, it should be borne in mind that the surface sampling procedure, al beit standardized, underestimates the numerical values of the fungi present. This is attributable to several rea sons; not all microorganisms are detached from the surface during sampling; some microorganisms will not be transferred from the swab to the culture me dium; and finally, the stress suffered by all microorgan isms, including fungi, during the sampling procedure affects their capacity for growth and therefore influ ences the final colony count. Because fungi can remain viable in the environment for long periods, surfaces constitute a much better reservoir of contamination for them than for bacteria. Thus, determining the con centration of fungi on surfaces is a meaningful way of assessing potential risk. For this reason, we only mea sured the sedimented load of fungi and not that of bacteria.
In light of what has been said, it is highly likely that the number of aspergilli actually present is greater. In terms of health risks, what is much more serious is the fact that the species identified were those (A. fumi-gatus and A. flavus) most frequently involved in cases of hospital aspergillosis.
From the epidemiologic standpoint, there is no sci entific proof that systematic vigilance against contam ination by fungi in at-risk hospital environments is effective.11 By contrast, environmental testing for the presence of fungi is meaningful if it is seen as a means of ensuring that air-conditioning systems and the be havior and organization of hospital staff are kept up to the desired standard.
Environmental sampling is an important method of checking the coherent application of all those prophy lactic procedures that should be implemented to ward off aspergillosis. It is therefore an expression of the environmental quality attained; such quality is influ enced by numerous factors, such as the behavior of the personnel, how the department is run, the charac teristics of the building and its installations, etc.
Clearly, departments equipped with air-conditioning systems that use HEPA (absolute) filters and in which the goal is to eliminate aspergilli entirely should install a monitoring system to check the overall quality attained.
Concerning the presence of fungi, surveillance pro cedures in protected environments are not currently standardized regarding the practical aspects, the meth ods of analysis, or the interpretation of results.11
Regarding health risks, it should nevertheless be emphasized that environmental sampling is a funda mental step in checking and controlling contamination by Aspergillus. Because the 3 sampling methods have different implications for health risks, they should be used simultaneously and the results that emerge should be evaluated together to assess the health risk accurately.
Active sampling, which measures the airborne mycotic load, expresses the direct risk of inhalation, whereas passive sampling, which reveals the sedi-menting load, expresses the indirect risk of inhalation; finally the sedimented load, that is to say the fungi adhering to deposited dust, indicates the potential risk. Indeed, the sedimented load is an indicator of the size of the reservoir from which the aspergilli can re-enter the environment; as a result of their
physical-chemical and aerodynamic features, spores that settle can develop in a short time and become airborne again by means of chance movements of the air caused by patients themselves, staff, or air-convection streams. Sedimented fungi are therefore able to re-contaminate the environment and to come into contact with patients again. Thus, the results of surface sampling seem to be the most significant in assessing the potential risk to which the patient is exposed. In this regard there is no consensus on the conidial density at which the risk of invasive aspergil losis (IA) is increased. Rhame12 reported a higher risk of IA when the average density of A. fumigatus was 0.9 CFU/m3. Arnow et al13 noted a marked decrease in the incidence of IA when Aspergillus density de creased from 1 to 2 to <0.2 CFU/m3. Sheretz et al2 reported no cases of IA after conidial density was reduced to 0.009 CFU/m3. Using a regression model, Al-berti et al14 found a significant relationship between the incidence of invasive nosocomial aspergillosis (ΙΝΑ) and the degree of fungal contamination of air and surfaces in conventional patient rooms (not equip ped with HEPA (absolute) filters) and common sites. In particular, they showed that peaks of air contamination by Aspergillus >2 CFU/m3 had a determining role in the relationship between environmental contamina tion and the occurrence of IA.
The results of the present study show that the use of air-conditioning systems can considerably reduce the concentration of aspergilli in the environment. Such systems cannot, however, eliminate the risk of con tamination unless they are scrupulously maintained and, at the same time, all the norms for environ mental prophylaxis indicated in the literature are respected.6·10·13·15-18
As amply reported by other investigators,9·11·15 the use of air-conditioning systems equipped with HEPA (absolute) niters is to be recommended in wards where there are patients with a level of polynucleate neutrophils below 500/mm3 persisting for 2 weeks or longer, or less than 100/mm3 whatever the duration of neutropenia.
It is practically impossible to eliminate the risk of aspergillosis entirely, but it can be reduced to a mini mum. Indeed, the use of an appropriate air-condition ing system (equipped with HEPA absolute filters), proper maintenance of the system itself, the applica tion of protocols for sanitization and staff behavior recommended for critical wards, etc, contribute to reducing the risk of aspergillosis significantly.
The need to do so is dictated, in the first place, by ethical considerations, in that the patient must be safe guarded, and in the second place by professional and economic considerations, in that the therapeutic ef forts undertaken should not be thwarted.
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