Previous Article | Next Article 
Journal of Clinical Microbiology, December 2001, p. 4598-4600, Vol. 39, No. 12
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.12.4598-4600.2001
LETTERS TO THE EDITOR
Use of Recombinant Mitogillin for Serodiagnosis of
Aspergillus fumigatus-Associated Diseases
 |
LETTER |
In a recent article, Weig et al. evaluated an enzyme-linked
immunosorbent assay (ELISA), using recombinant mitogillin for the
detection of antibodies in patients with Aspergillus
fumigatus-associated diseases (3). The authors
reported a good correlation between production of immunoglobulin G
(IgG) antibody against mitogillin and clinical diseases, with
sensitivities of 100, 64, and 60% for aspergilloma (AO), invasive
pulmonary aspergillosis (IPA), and invasive disseminated aspergillosis
(IDA), respectively, where the corresponding specificity of the ELISA
was 95.4%, using a cutoff value of the mean optical density (OD) of
307 normal blood donor sera plus 2 standard deviations (SD).
Although the apparently high sensitivities of the ELISA look
encouraging, we think that the interpretation of the results was
misleading due to the choice of a low cutoff value. For rare diseases
such as AO, IPA, and IDA, in order to eliminate the false positives,
high specificities (over 99%) are desirable. In our recently published
articles on ELISA for antibody and antigen detection in patients with
penicilliosis marneffei, a cutoff value of the mean plus 10 SD
was chosen, for a specificity of 100% (1, 2). However, in
the study of Weig et al., a low cutoff value of the mean plus 2 SD was
chosen, leading to a specificity of just 95.4% (3).
The ELISA would have much lower sensitivities if the mean plus 3 SD,
the mean plus 4 SD, or the mean plus 5 SD were chosen as the cutoff
value. Since an index of 0.75 (serum sample no. 96) was regarded as
positive and an index of 0.73 (serum sample no. 63) was regarded as
negative, the value obtained by dividing the mean plus 2 SD by the mean
plus 3 SD should lie between 0.73 and 0.75. If we assume that the mean
plus 2 SD divided by the mean plus 3 SD equals 0.74, 0.26 times the
mean would equal 0.22 of the SD. Hence, the mean plus 4 SD divided by
the mean plus 3 SD and the mean plus 5 SD divided by the mean plus 3 SD
can be calculated as 1.26 and 1.52, respectively. Using the IgG OD index values of the serum samples shown on pages 1725 to 1727 of
reference 3, a scattergram can be generated (Fig.
1) and the corresponding sensitivities of
the ELISA using the mean plus 3 SD, the mean plus 4 SD, and the mean
plus 5 SD as the cutoff values can be calculated (Table
1). In order to achieve a high specificity (over 99%), a cutoff value of at least the mean plus 4 SD
or the mean plus 5 SD has to be chosen. At these cutoff values, the
corresponding sensitivity of the ELISA for AO would fall to below 90%,
whereas those for IPA and IDA would be less than 20%. In fact, it is
not surprising to have low sensitivities for IPA and IDA, as patients
suffering from invasive aspergillosis are usually severely
immunocompromised (4) and production of antibodies is
greatly impaired.
View larger version (19K):
[in this window]
[in a new window]
|
FIG. 1.
Scattergram showing the IgG OD index values of serum
samples obtained from patients with AO, IPA, or IDA as measured by the
ELISA using recombinant mitogillin.
|
|
| |
FOOTNOTES |
*
Phone: (852) 285 54892
Fax: (852) 285 51241
E-mail: hkumicro{at}hkucc.hku.hk
| |
REFERENCES |
| 1.
|
Cao, L.,
D. L. Chen,
C. Lee,
C. M. Chan,
K. M. Chan,
N. Vanittanakom,
D. N. Tsang, and K. Y. Yuen.
1998.
Detection of specific antibodies to an antigenic mannoprotein for diagnosis of Penicillium marneffei penicilliosis.
J. Clin. Microbiol.
36:3028-3031[Abstract/Free Full Text].
|
| 2.
|
Cao, L.,
K. M. Chan,
D. Chen,
N. Vanittanakom,
C. Lee,
C. M. Chan,
T. Sirisanthana,
D. N. Tsang, and K. Y. Yuen.
1999.
Detection of cell wall mannoprotein Mp1p in culture supernatants of Penicillium marneffei and in sera of penicilliosis patients.
J. Clin. Microbiol.
37:981-986[Abstract/Free Full Text].
|
| 3.
|
Weig, M.,
M. Frosch,
K. Tintelnot,
A. Haas,
U. Groß,
B. Linsmeier, and J. Heesemann.
2001.
Use of recombinant mitogillin for improved serodiagnosis of Aspergillus fumigatus-associated diseases.
J. Clin. Microbiol.
39:1721-1730[Abstract/Free Full Text].
|
| 4.
|
Yuen, K. Y.,
P. C. Y. Woo,
M. S. M. Ip,
R. H. S. Liang,
E. K. W. Chiu,
H. Siau,
P. L. Ho,
F. F. Chen, and T. K. Chan.
1997.
Stage-specific manifestation of mold infections in bone marrow transplant recipients: risk factors and clinical significance of positive concentrated smears.
Clin. Infect. Dis.
25:37-42[Medline].
|
| | | | |
Patrick C. Y. Woo
Andy S. P. Leung
Susanna K. P. Lau
Ken T. K. Chong
Department of Microbiology
The University of Hong Kong
Queen Mary Hospital
Hong Kong
|
| | | | |
Kwok-Yung Yuen*
Department of Microbiology
The University of Hong Kong
University Pathology Building
Queen Mary Hospital, and
HKU-Pasteur
Research Centre
Hong Kong
|
Authors' Reply
A test specificity of >99%, as has been suggested by Woo et al.,
seems to be an unjustified postulation for the recombinant mitogillin
enzyme-linked immunosorbent assay (ELISA), as the test is not designed
to screen a large unbiased population (low prevalence of the disease).
Instead, invasive aspergillosis (IA) and aspergilloma (AO) are diseases
that occur in well-defined risk patients (high prevalence of the
disease in the population studied) (2).
Approximately one-third of the patients with acute IA initially
show no definitive signs, though a fatal progression rate of the
disease becomes manifest (1). Unfortunately, the
diagnostic tools developed to date have low sensitivities
(2) and antifungal therapy is initiated empirical and
belated. The very high mortality rate of IA (>80 to 90%) could be
reduced when a sensitive test system leads to an early diagnosis and
well-timed therapy.
The usefulness of the mitogillin ELISA for a given patient at risk
depends largely, besides on its specificity and sensitivity, on its
positive and negative predictive values and the probability for
false-positive and for false-negative test results. The latter test
quality-defining parameters are dependent on the prevalence of the
disease in the population studied.
The ability of a test to discriminate diseased cases from healthy
controls is evaluated using receiver operating characteristic (ROC)
curve analysis (3). An index of the test accuracy is the
area under the ROC curve. Each point on the ROC plot represents a
sensitivity-specificity pair corresponding to a particular cutoff value. A widely used method to determine the cutoff point based on a
ROC curve is to maximize the Youden index (5). The ROC plot data allow calculation of the most effective cutoff value, when
the prevalence of the disease is ascertained. The frequency of IA is
known to be high in risk patients, but it varies substantially from
risk group to risk group and from center to center (1). Since there is no "gold standard" in the laboratory diagnosis of
IA, the true prevalence of IA in different risk groups is difficult to
estimate (2).
ROC curve analyses of the recombinant anti-mitogillin IgG ELISA were
done with data from blood donors (n = 307) and patients suffering from aspergillosis (n = 114); the analytic
data were generated using SPSS software (version 10.0.7; SPSS Inc.
Headquarters, Chicago, Ill.) (Fig. 1 and
Table 1). The ROC curve analyses of our preliminary data show
that our simplified approach (the
cutoff was the mean optical density [OD] plus 3 SD standard
deviations [SD], calculated from blood donors; the borderline
was the mean plus 2 SD) was adequate for a first evaluation of the
test. For the group of AO patients, the maximal Youden index lies
exactly between the positive and borderline cutoff values used in our study. The results of the analysis confirm the usefulness of the recombinant anti-mitogillin antibody ELISA for the diagnosis of A. fumigatus-related diseases (area under ROC curve > 0.9). The analysis indicate further that it might be possible to define different cutoff values for different patient groups (e.g., OA versus
IA) in order to increase the diagnostic accuracy of the test (data not
shown). However, in our opinion this should be done in a later study
with an extended number of patients from whom reliable data (proven
disease) are available.
View larger version (18K):
[in this window]
[in a new window]
|
FIG. 1.
ROC curve. See the text and Table 1 for explanations of
the data used to generate the curve. The solid arrow marks the point
with the maximal Youden index. The cutoff value used in the study of
Weig et al. (4) is indicated with a dashed arrow, and the
cutoff value proposed by Woo et al. is indicated with a dotted
arrow.
|
|
| |
FOOTNOTES |
*
Phone: 49 551397099
Fax: 49 551395861
E-mail: mweig{at}gwdg.de
| |
REFERENCES |
| 1.
|
Denning, D. W.
2000.
Aspergillus species, p. 2674-2685.
In
G. L. Mandell, J. E. Bennett, and R. Dolin (ed.), Principles and practice of infectious diseases. Churchill Livingstone, Philadelphia, Pa.
|
| 2.
|
Latge, J. P.
1999.
Aspergillus fumigatus and aspergillosis.
Clin. Microbiol. Rev.
12:310-350[Abstract/Free Full Text].
|
| 3.
|
Metz, C. E.
1978.
Basic principles of ROC analysis.
Semin. Nucl. Med.
14:109-121.
|
| 4.
|
Weig, M.,
M. Frosch,
K. Tintelnot,
A. Haas,
U. Groß,
B. Linsmeier, and J. Heeseman.
2001.
Use of recombinant mitogillin for improved serodiagnosis of Aspergillus fumigatus-associated diseases.
J. Clin. Microbiol.
39:1721-1730.
|
| 5.
|
Youden, W. J.
1950.
Index for rating diagnostic tests.
Cancer
3:32-35[CrossRef][Medline].
|
| | | | |
Michael Weig*
Uwe Groß
Department of Bacteriology
University of Goettingen
Kreuzbergring 57
37075 Göttingen, Germany
|
| | | | |
Sebastian Domhof
Edgar Brunner
Department of Medical Statistics
University of Goettingen
Göttingen, Germany
|
Journal of Clinical Microbiology, December 2001, p. 4598-4600, Vol. 39, No. 12
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.12.4598-4600.2001
This article has been cited by other articles:
-
Chan, C.-m., Woo, P. C. Y., Leung, A. S. P., Lau, S. K. P., Che, X.-y., Cao, L., Yuen, K.-y.
(2002). Detection of Antibodies Specific to an Antigenic Cell Wall Galactomannoprotein for Serodiagnosis of Aspergillus fumigatus Aspergillosis. J. Clin. Microbiol.
40: 2041-2045
[Abstract]
[Full Text]
