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Roberto D'Amico a Mario Negri Institute for Pharmacological
Research, 20157 Milan, Italy, b Maggiore Ospedale
IRCCS, 20122 Milan
Correspondence to: Dr A
Liberati, Italian Cochrane Centre, Laboratory of Health Services
Research, Mario Negri Institute, Via Eritrea 62, 20157 Milan, Italy
Cochrane{at}irfmn.mnegri.it
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Abstract |
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Objective: To determine whether antibiotic
prophylaxis reduces respiratory tract infections and overall mortality
in unselected critically ill adult patients.
Design: Meta-analysis of randomised controlled trials
from 1984 and 1996 that compared different forms of antibiotic prophylaxis used to reduce respiratory tract infections and mortality with aggregate data and, in a subset of trials, data from individual patients.
Subjects: Unselected critically ill adult patients;
5727 patients for aggregate data meta-analysis, 4343 for confirmatory meta-analysis with data from individual patients.
Main outcome measures: Respiratory tract infections
and total mortality.
Results: Two categories of eligible trials were
defined: topical plus systemic antibiotics versus no treatment and topical preparation with or without a systemic antibiotic versus a
systemic agent or placebo. Estimates from aggregate data meta-analysis of 16 trials (3361 patients) that tested combined treatment
indicated a strong significant reduction in infection (odds ratio 0.35; 95% confidence interval 0.29 to 0.41) and total mortality (0.80; 0.69 to 0.93). With this treatment five and 23 patients would need to be
treated to prevent one infection and one death, respectively. Similar
analysis of 17 trials (2366 patients) that tested only topical
antibiotics indicated a clear reduction in infection (0.56; 0.46 to 0.68) without a significant effect on total mortality (1.01;
0.84 to 1.22). Analysis of data from individual patients yielded
similar results. No significant differences in treatment effect by
major subgroups of patients emerged from the analyses.
Conclusions: This meta-analysis of 15 years of
clinical research suggests that antibiotic prophylaxis with a
combination of topical and systemic drugs can reduce respiratory
tract infections and overall mortality in critically ill patients.
This effect is significant and worth while, and it
should be considered when practice guidelines are
defined.
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Key messages
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Introduction |
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Nosocomial infections, especially pneumonia, are an important cause of morbidity and mortality in critically ill patients. The incidence of pneumonia in such patients ranges between 7% and 40%, and the crude mortality from ventilator associated pneumonia (VAP) may exceed 50%. Although not all deaths in patients with this form of pneumonia are directly attributable to infection, it has been shown to contribute to mortality in intensive care units independently of other factors that are also strongly associated with such deaths.1 In a case-control study of ventilated patients an increase in mortality of 27% was attributable to ventilator associated pneumonia.2 Considerable efforts have been made to develop and evaluate methods for reducing respiratory infections. One strategy involves the use of selective decontamination of the digestive tract (SDD). Different decontamination protocols have been used in different trials, and investigators often disagree on its most appropriate definition. Traditionally, selective decontamination of the digestive tract indicates a method designed to prevent infection by eradicating and preventing carriage of potentially pathogenic aerobic microorganisms from the oropharynx, stomach, and gut. It consists of antibiotics applied topically to the oropharynx and through a nasogastric tube. In many trials treatment with systemic antibiotics has been added in the first days after patients are admitted to prevent "early" infections.
A decontamination regimen based on oral non-absorbable antibiotics was first used in 1984 by Stoutenbeek et al in a group of patients with multiple trauma.3 The incidence of nosocomial infections was reduced from 81% to 16% in a non-randomised comparison with a historical control group. Further studies tested the efficacy of decontamination in patients in intensive care with morbidity related to infection as the main end point. The results showed that decontamination reduced infection, but it was not clear whether there was a reduction in mortality.
Between 1991 and 1995 five different meta-analyses on the effect of antibiotic prophylaxis on infections and mortality were published.4-8 Their results are summarised in table 1. All confirmed a significant reduction in infections, though the magnitude of the effect varied from one review to another. The estimated impact on overall mortality was less evident and generated considerable controversy on the cost effectiveness of the treatment. Only one among the five available reviews, however, suggested that a weak association between respiratory tract infections and mortality and lack of sufficient statistical power may have accounted for the limited effect on mortality.5 The authors suggested that, given the baseline risk of death in the populations typically enrolled in existing trials, between 2000 and 3000 patients were probably needed to detect reliably a relative reduction in mortality in the 10%-20% range.5
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We report here on an updated and refined meta-analysis made possible by the enthusiastic collaboration of most investigators in the topic. Besides updating the results by using data from randomised controlled trials published since the 1993 paper,5 there are two main differences between this and previously published meta-analyses. The first is the way trials have been grouped to test the effectiveness of the treatment. Contrary to previous practice we have separately analysed trials that tested combinations of topical and systemic antibiotics from trials that tested the effect of topical drugs alone. The second is that information for individual patients was sought from all trials. Results from this more refined type of meta-analysis, which proved feasible in 4343/5727 (76%) patients, are reported and compared with findings from the corresponding aggregate datasets.
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Patients and methods |
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Search strategy
We searched for randomised controlled trials published from
January 1984 to December 1996. Studies were identified through Medline
(MeSH keywords: "Intensive care units," "Critical care," "Antibiotic combined therapeutic use," "Antibiotics combined
administration and dosage," "Respiratory tract infections
prevention and control" with the keyword "SDD"). Other studies
were evaluated because they were listed in previous meta-analyses. The
organiser of the first European Consensus Conference on Intensive Care
Medicine (held in December 1991) also provided a list of all
investigators who had ever published on the topic. An additional search
focused on proceedings of scientific meetings held on the subject and personal contacts were established with other known investigators. No
formal inquiry was made through pharmaceutical companies.
Eligibility criteria for studies
All trials, published and unpublished, which tested the effect of
antibiotic prophylaxis for the prevention of respiratory tract
infections and deaths in unselected critically ill adult patients were
considered. No language restriction was applied. Only randomised
trials were accepted to guarantee control of selection bias.
Studies that were determined on closer scrutiny not to be properly
randomised (see definition below) were not included.
those in which topical
antibiotics were tested against an untreated group (S Jacobs, M
Zuleika, personal communication)35-44 and those in which
the combination of topical plus a systemic drug was compared with a
protocol based on a systemic antibiotic agent only.45-50 Any combination of topical or systemic antibiotic (that is, type of
drugs) was accepted.
Data extraction and relevant information
sought
The results of the meta-analysis of aggregate data presented in
table 2 are based on 33 trials; in the other tables, however, more
studies and patients are shown because the two trials with three arms
were split into two parts in which two different treatments were
compared with the same control group.
33 49
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Quality assessment of studies
Study quality was assessed by looking at methods of randomisation
(blind versus open) and use of blinding techniques (double blind versus
unblind studies). The randomisation procedure was classified as blind
when it was done by telephone through a pharmacy or a central office or
by using sealed envelopes. It was classified as open when it was done
with a computer generated list directly managed by study investigators
or when patients were allocated by odd-even number or other types of
open lists.
Outcome measures and statistical analysis
Two main outcome measures were considered: respiratory tract
infections and overall mortality. No restriction was made on type of
infection considered and on diagnostic criteria for infection chosen by
the trialists. Both tracheobronchitis and pneumonia were acceptable.
Both primary (diagnosed within 48 hours after admission) and acquired
(diagnosed after 48 hours after admission) infections were considered,
even if we used data on acquired infections when information on both
was available. Mortality was evaluated at hospital discharge, if this
information was available, otherwise mortality in the intensive care
unit was considered.
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1.24+1.484*(SAPS).52 Patients were grouped into
three mutually exclusive classes within groups defined by the main
diagnostic categories (medical, surgical, trauma) according to severity
of disease. APACHE II cut off points were chosen to define low or
medium or high severity with reference to the "expected mortality
rate" (<10%, 10-60%, >60%).53
In addition to odds ratios of each outcome in each trial, computed with
the fixed effects model (Peto method),54 we estimated the
number of patients in intensive care who would need to be treated to
prevent one infection and one death. The calculation was based on the
median rates of infections and deaths in untreated controls and the
common odds ratio for all trials.
We carried out two prespecified subgroup analyses on the basis of
quality criteria within the above mentioned two main groups of trials:
quality of randomisation procedures (blind versus open) and blinding of
patients and doctors to allocated treatment (double blind versus
unblind). For analyses on data on individual patients odds ratios,
stratified by prognostic factor, were calculated with the fixed effects
model.
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Results |
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Information from 33 trials that between 1984 and 1996 enrolled a total of 5727 patients was the base for the aggregate data meta-analysis (table 2). Data on individual patients were obtained from 25/33 trials including 4343/5727 (76%) patients.
Respiratory tract infections
Evaluation from meta-analysis of aggregate data
Overall, results from 30 trials including 4898 patients were
available for the analysis of the effects of different types of
antibiotic prophylaxis on respiratory tract infections: 1184 patients
developed one or more infections (S Jacobs and M Zuleika, personal
communication).
19-26 28-35 37-45 47-50
The prevalence of respiratory infections was 16% among treated patients and 36% among controls in trials that used a combination of topical plus systemic antibiotics and 18% and 28%, respectively, in trials that tested the effectiveness of topical prophylaxis alone. Overall, the odds ratio was lower than unity in all but two comparisons 44 49 and reached conventional significance (P<0.05) in 21/32 comparisons.
The results indicated a strong protective effect of the combination of topical and systemic treatment (odds ratio 0.35; 95% confidence interval 0.29 to 0.41) (fig 1). A clear though less extreme protection was also seen when treatment effect was explored in trials that tested topical antibiotics (0.56; 0.46 to 0.68)(fig 2).
These results suggest that 5 (4 to 5) and 9 (7 to 13) patients would need to be treated to prevent one infection, depending on whether a combination of topical and systemic drugs or a topical antibiotic only is tested. This assumes the median values of 44% and 32% for baseline risk, respectively, as seen among control patients.
The effect of the quality of randomisation could meaningfully be explored only among trials that tested the relative effectiveness of topical antibiotic agents (given that all but two trials of the topical plus systemic group had blind randomisation): trials with blind randomisation showed a greater effect (0.51; 0.40 to 0.66) compared with those in which the procedure was open (0.66; 0.48 to 0.91). Results from double blind trials did not differ from those obtained in unblind studies.
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Evaluation from meta-analysis of data from individual patients
The results from the 25 studies for which data were
provided by the trialist are reported in tables 3 and 4 (S Jacobs
and M Zuleika, personal
communication).
20-24 28-35 37-42 45 47-50
Odds
ratios and relative confidence intervals are presented within specific groups of diagnostic category and severity score. The effect of the
treatment on infections is shown for both types of treatment protocols
that is, topical plus systemic (0.40; 0.33 to 0.49) and
topical alone (0.61; 0.49 to 0.75). The results seem more pronounced,
however, in trials in which the combination was used.
The widespread belief that the treatment is more effective in patients
with intermediate severity scores (that is, APACHE II score 15-29) and
less effective among "medical" patients was not supported by the
data from trials that tested the topical and systemic combination. The
extent of the treatment effect was quite consistent across disease
categories and severity groups. Data from trials that tested topical
antibiotics are more difficult to interpret because of the small number
of patients in the highest APACHE II category
that is,
30.
Overall, these results did not differ substantially from those obtained by pooling data from trials for which data on individual patients were not available (table 5), suggesting that no bias was introduced by lack of data provided by study investigators.
Mortality
Evaluation from meta-analysis of aggregate data
A total of 1515 deaths occurred in the 33 trials with 5727 patients available for analysis (S Jacobs and M Zuleika, personal communication).19-50 The mortality was 24% in treated
patients and 30% in controls for trials that tested a combination
of topical plus systemic antibiotics and 26% in control and treated
patients for trials that tested the effectiveness of topical treatment. The odds ratio was lower than unity in 23/35 comparisons but reached significance in only two trials
27 31
; no trial suggested
a significant harmful effect of antibiotic prophylaxis. Results indicate a significant reduction in mortality attributable to the use
of a combination of topical and systemic treatment (0.80; 0.69 to 0.93)
(fig 3). Twenty three patients (14 to 68) would need to be treated
to prevent one death (if we assume a median baseline risk of 29% among
control patients). No effect was seen when trials that tested topical
antibiotics alone were analysed (1.01; 0.84 to 1.22) (fig
4).
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While analyses by quality of randomisation did not affect the results, reduction in mortality among trials that tested a combination of topical and systemic antibiotics was greater in trials that used a double blind design (0.63; 0.48 to 0.83) compared with unblind studies (0.90; 0.74 to 1.08).
Evaluation from meta-analysis of data from individual
patients
Results from 25 studies are reported in table 6 and 7
(S Jacobs and M Zuleika, personal
communication).
20-24 28-35 37-42 45 47-50
Odds
ratios with their relative confidence intervals are presented within
specific groups of diagnostic categories and severity scores. Similarly
to the results derived from the corresponding aggregate data analysis,
a significant reduction in overall mortality was observed for trials
that tested a combination of topical and systemic antibiotics (0.79;
0.65 to 0.97) but not from studies that tested topical drugs alone
(1.02; 0.81 to 1.30). Treatment effect did not vary substantially by
main diagnostic category.
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Overall, these results did not differ substantially from those obtained by pooling data from trials for which individual patient data were available (table 5).
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Discussion |
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Effectiveness of antibiotic prophylaxis
Since its introduction as a method designed to prevent infection
in critically ill patients the effectiveness of antibiotic prophylaxis
has remained controversial.3 The lack of standard protocols and insufficient numbers of patients have made it difficult to derive meaningful conclusions from individual randomised controlled trials. Despite initial enthusiasm after results from early
uncontrolled studies and initial trials, antibiotic prophylaxis
as
tested in available trials
is not widely used in intensive care units.
The concern about the risk of long term emergence of antibiotic
resistance and of increasing costs dominates in recent American
documents based on expert opinions on prevention of infections such as
the Guidelines for Prevention of Nosocomial Pneumonia
recently published by the Centers for Disease Control and
Prevention55 and the consensus statement of the American
Thoracic Society on Hospital-Acquired Pneumonia in
Adults.56 A conservative attitude in introducing a
new treatment into practice is understandable as long as doubts exist
about its efficacy. In fact studies on prevention of ventilator associated pneumonia in patients in intensive care units are complex because patients are heterogeneous, diagnosis of pneumonia is controversial, and outcome depends on many factors. Although the ability of antibiotic prophylaxis to reduce respiratory tract infections emerged with remarkable consistency across individual trials, the effect on mortality was significant in only two. It was
never fully realised that this was probably because of the small sample
sizes of individual studies and, possibly, the weak association between
respiratory infections and mortality.
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with a more pronounced effect when patients are treated
with the combination of topical plus systemic antibiotics. This effect
was consistent for all subgroups of patients regardless of study design
(blind or open randomisation, double blind or unblind studies).
Overall, these results seem convincing even though it is acknowledged
that no diagnostic test or procedure is ideal for diagnosing
respiratory infections in patients in intensive care units.
The important new finding from this meta-analysis is that for
prophylactic regimens that combine topical and systemic antibiotics there is also a relevant reduction of overall mortality.
Given the enthusiastic collaboration provided by most investigators and
the efforts to include unpublished studies, it is unlikely that we have
missed any important trials conducted so far. Moreover, as nearly all
trials did not show significant reduction in mortality on their own,
there is no good reason to believe that publication bias represents a
major problem in this literature.
The inability to obtain data on individual patients from all trials is
unlikely to have biased results of the meta-analysis of such data. As
table 5 shows, results of trials for which we could not obtain
information on individual patients were not substantially different
from those with such data available. Further details on patients mix
and treatments can be found in the version of this review available in
the Cochrane Library.58
Insights from meta-analysis on data from individual patients
A methodological strength of this review is the availability of
data from individual patients for a large number of trials. Firstly,
this allowed a comprehensive quality check of the data, which, by and
large, confirmed the validity of the aggregate analysis. Secondly, the
availability of data on individual patients permitted the
identification of subgroups more likely to benefit from treatment. There is a widespread belief among clinicians that some patients may
respond more favourably to the treatment. For example, patients categorised according to their underlying conditions as surgical or
trauma patients and those with medium severity of illness scores are
expected to respond more favourably to antibiotic prophylaxis than
those labelled as medical patients or with low or high severity scores.
Our subgroup analyses, however, do not support this view. The data in
tables 3, 4, and 6 suggest that when the treatment works there is no
difference in the size of treatment effect of the combined prophylaxis
regimens among medical, surgical, and trauma patients within
corresponding severity of disease.
Implications for practice
This systematic review indicates that a protocol that uses a
combination of topical and systemic antibiotics reduces both the
occurrence of respiratory tract infections and overall mortality. The
effect of this intervention expressed in terms of patients needed to be
treated to prevent one infection and one death is substantial
five and
23, respectively
and compares favourably with several interventions
largely used in clinical practice. Though 8/16 trials used an identical
regimen, including polymyxin, tobramycin, and amphotericin as the
topical combination and cefotaxime as the systemic
component,
19 21 24-26 28 29 50
this review does not
allow a unique regimen to be recommended. The use of topical
antibiotics alone, however, is not justified by available data.
Implications for research
The number of trials examining antibiotic prophylaxis provides
sufficient statistical power to detect a moderate but worthwhile effect
of the treatment on mortality.5 According to this
systematic review a protocol of a combination of topical and systemic
antibiotics should be the standard against which new treatments are
tested.
as it may obscure the fact
that the effective digestive decontamination achieved by different
regimens can vary62-64
we did not envision a viable alternative and preferred to be consistent with the other published meta-analyses. On the other hand, even if results of all available trials are combined
as has been done in other recent
meta-analyses6-8
the reduction in mortality is still
significant (odds ratio 0.88; 95% confidence interval 0.78 to 0.98).
A logical next step for future trials would thus be the comparison of
this protocol against a regimen of a systemic antibiotic agent only to
see whether the topical component can be dropped. We have already
identified six such trials
31 45-49
but the total number
of patients so far enrolled (1056) is too small for us to be confident
that the two treatments are really equally effective. If the hypothesis
is therefore considered worth testing more and larger randomised
controlled trials are warranted.
Trials of this kind, however, would not resolve the relevant issue of
treatment induced resistance. To produce a satisfactory answer to this,
studies with a different design would be necessary. Though a detailed
discussion goes beyond the scope of this paper, studies in which the
intensive care unit rather than the individual patient is the unit of
randomisation and in which the occurrence of antibiotic resistance is
monitored over a long period of time should be undertaken. One or more
coordinated trials of this sort should be able to enrol a few thousands
patients and should be designed in a pragmatic fashion concentrating on
outcomes such as mortality, resistance, and costs. On the basis of our
results it is not clear whether enrollment in these trials should be
limited to specific categories of patients or should be open to all
patients in intensive care. Given the uncertainty on this issue that
stems from our analysis, trials with less strict eligibility criteria would be preferable. The growing collaboration among intensivists in
the European Union Biomed Programme could provide a framework for
designing and carrying out efficient studies aimed at settling this
important research question.
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Acknowledgments |
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The steering committee comprised DJ Cook (McMaster University Faculty of Health Sciences, Ontario), J Carlet (Hopital Saint-Joseph, Paris), M Langer (Ospedale Maggiore Policlinico IRCCS, Milan), P Loirat (CMC FOCH Suresnes, Paris), and HFK Van Saene (University of Liverpool, Liverpool). The investigators who were coauthors of this paper and provided data for meta-analysis of data from individual patients were SJA Aerdts (Sophia Hospital, Zwolle, the Netherlands); P Blair, BJ Rowlands, H Webb, and K Lowry (Royal Victoria Hospital, Belfast); JP Bowland, D Sadler, A Stewart, and J Pollock (Health Science Center Charlestone, West Virginia University); FR Cockerill and RI Thomson (Mayo Clinic, Rochester, Minnesota); M Ferrer and A Torres (Servei de Pneumologia, Hospital Clinic, Barcelona); RG Finch, P Tomlinson, and G Rocker (Nottingham City Hospital, Nottingham); H Gastinne (on behalf of the French Study Group on Selective Decontamination of the Digestive Tract); B Georges (Hôpital de Rangueil, Toulouse); JMJ Hammond and PD Potgieter (Groote Schuur Hospital, Cape Town); S Jacobs and M Zuleika (Riyadh Armed Forces Hospital, Riyadh); AM Korinek (Hôpital Pitié-Salpêtrière, Paris); AN Laggner (Vienna General Hospital, Vienna); W Lingnau (Leopold-Franzens-Universitat Innsbruck, Innsbruck); A Martinez-Pellus and J Rodriguez-Roldan (General Hospital, Murcia); M Palomar (Hospital Vall d'Hebron, Barcelona); J Pugin and P Suter (University Hospital, Geneva); C Martin, B Quinio, and J Albanese (Hôpital Nord, Marseilles); LA Rocha (Hospital Juan Canalejo, La Coruna); M Sanchez-Garcia (Hospital PPE Asturias, Alcala de Henares); CP Stoutenbeek (Academisch Ziekenhuis, Universiteit van Amsterdam, Amsterdam); C Ulrich and JE Harinck-De Weerd (Westeinde Hospital, The Hague); J Verhaegen and C Verwaest (University Hospital, Louvain); R Winter (Queen's Medical Centre University Hospital, Nottingham).
We thank L Brazzi (Ospedale Maggiore IRCCS, Milan) for his help and contribution in the earlier phases of this project, C Brun-Buisson (Hôpital Henry Monor, Creteil, Paris) for his useful comments and criticisms on several earlier drafts of this manuscript, and D Baxby (University of Liverpool, Liverpool) for editing an earlier draft of this manuscript. An earlier version of this paper won the Thomas C Chalmers Award at the fourth Cochrane Colloquium in Adelaide in October 1996.
Contributors: RD'A discussed core ideas of the project, participated in the design of the protocol for the meta-analysis of data from individual patients, had the main responsibility for data analysis and interpretation, and participated in writing the paper. SP discussed core ideas of the project, participated in the design of the protocol for the meta-analysis of data from individual patients, organised data collection, maintained contacts with the trialists checking data validity and accuracy, contributed to the interpretation of results, and participated in writing the paper. CL participated in the design of the protocol for the meta-analysis of data from individual patients, organised data collection, maintained contacts with the trialists checking data validity and accuracy, and contributed to the interpretation of results. VT discussed core ideas of the project, participated in the design of the protocol for the meta-analysis of data from individual patients, contributed to data analysis, and provided useful suggestions to the various drafts of the paper. AT designed and prepared the software for data management and helped with data analysis. AL initiated and coordinated the earlier phases of this research, discussed core ideas of the project, participated in the design of the protocol for the meta-analysis of data from individual patients, contributed to data analysis and interpretation, and had the main responsibility for writing the paper.
Funding: The meta-analysis of data from individual patients was supported by a grant from Hoechst Marion Roussel, Italy.
Conflict of Interest: None.
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References |
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Appendix |
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