Acta Dermato-Venereologica 98-10CompleteContent | Page 21

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SHORT COMMUNICATION
Diagnostic Value of T-SPOT.TB Test in Cutaneous Mycobacterial Infections
Yanqing CHEN 1,2# , Haiqin JIANG 1,2# , Wenyue ZHANG 1,2 , Zhiming CHEN 1,2 , Youming MEI 1,2 , Hao CHEN 1,2 , Ying SHI 1,2 , Wei
GAO 1,2 , Le WANG 1,2 , Santosh CHOKKAKULA 1,2 and Hongsheng WANG 1,2 *
1
Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, 12 Jiangwangmiao St., Nanjing 210042,
Jiangsu, and 2 Jiangsu Key Laboratory of Molecular Biology for Skin Diseases and STIs, St. Nanjing, Jiangsu, China. *E-mail: whs33@vip.
sina.com
#
These authors contributed equally.
Accepted Jul 27, 2018; Epub ahead of print Aug 7, 2018
Detection of pathogens in skin infections caused by my-
cobacteria is difficult. Interferon-gamma release assay
(IGRA), a preferred method for the diagnosis of latent
tuberculosis infection (LTBI), has shown the capacity to
detect mycobacterial infections (1–4). IGRAs have higher
specificity over the tuberculin skin test, as they are based
on Mycobacterium tuberculosis antigens encoded on RD1
(secretory antigen target 6 and culture filtrate protein 10).
RD1 is absent in Bacillus Calmette–Guérin (BCG) and
most environmental mycobacteria. However, a high degree
of similarity was found in both the amino-acid sequences
and the gene sequences encoding the RD1 antigens of M.
tuberculosis and various other mycobacteria, i.e. M. ma-
rinum, M. szulgai, M. kansasii, and M. gordonae (1, 5–7).
The aim of this study was to prospectively explore the di-
agnostic value of the T-SPOT.TB test (Oxford Immunotec
Ltd., Abingdon, UK), a representative IGRA, in cutaneous
infections with RD1-possessing mycobacteria, including
M. tuberculosis and RD1-possessing nontuberculous my-
cobacteria (NTM). Furthermore, we evaluated the changes
in T-SPOT.TB test results after antibiotic treatment.
METHODS
Between July 1, 2015 and December 30, 2017, we conducted the
study at the Institute of Dermatology, Chinese Academy of Medical
Sciences. All clinically suspected cases of cutaneous tuberculosis
or NTM infections were screened prospectively. Ethics approval
(2012-KY/LC-021) was obtained from our ethics committees.
Informed consent was obtained from the participants.
There is currently no diagnostic method regarded as the gold
standard for diagnosis of cutaneous tuberculosis, cutaneous infec-
tion of NTM and cutaneous fungal infection, so all eligible subjects
were diagnosed with these diseases based on the following criteria:
1) chronic skin lesions, 2) pathology showing infectious granulo-
mas, 3) molecular biological methods for the culture organism or
biopsy samples confirming the corresponding disease.
Patients who met the following conditions were excluded: 1)
having active tuberculosis of any organ except the skin; 2) having
a history of anti-mycobacterium antibiotic treatment; 3) being
ruled out by pathology; 4) refusing to participate.
Peripheral venous blood was collected for T-SPOT.TB test
before treatment. Subjects in the group of cutaneous infection of
RD1-possessing mycobacteria were followed up on every two
months, and after 6 months of antibiotic therapy, they were further
reevaluated using T-SPOT.TB test. Treatment of cutaneous tuber-
culosis followed the recommended guidelines by the WHO, which
consist of an intensive phase for 2 months (isoniazid, rifampicin,
ethambutol, and pyrazinamide) followed by a maintenance phase
for 4 months (isoniazid and rifampicin) (8). Treatment for cuta-
neous NTM infection was designed based on drug susceptibility
tests. For those who did not participate in such tests, we utilized
empiric antibiotic therapies.
The procedure of T-SPOT.TB followed the manufacturer’s
guidelines. The high spot numbers of Panel A minus Nil Control
(PA) and Panel B minus Nil Control (PB) were recorded as spot
forming cells (SFCs). Molecular biological methods were based
on PCR and sequencing of the 16S rRNA and hsp65 genes (9).
Homology analyses were conducted to define the strain.
Continuous variables were summarized using mean (standard
deviation) for normally distributed data and using median (in-
terquartile range (IQR)) for non-normally distributed data. The
difference in age between groups was assessed by Mann–Whitney
test. The differences in sex, underlying conditions, trauma history
and HIV status were assessed by Chi-squared test. Positivity
rates across groups were compared using Chi-squared tests. The
median SFCs among groups were compared by Kruskal–Wallis
test. Changes in positivity rates and SFCs before and after therapy
were determined by McNemar’ test and Wilicoxon rank sum test,
respectively. Statistical significance was considered as p < 0.05.
Statistical analyses were performed using IBM SPSS 19.0.
RESULTS
A total of 293 clinically suspected cases of cutaneous
mycobacterial infection were screened for the study (Fig.
S1 1 ). A total of 64 participants were eligible. Among them,
46 (71.9%) were classified as cutaneous infection of
RD1-possessing mycobacterium, 8 (12.5%) as cutaneous
infection of RD1-negative NTM, and 10 (15.6%) as cu-
taneous fungal diseases. The basic characteristics of the
64 participants are shown in Table SI 1 . Forty (87.0%) of
46 cutaneous infections with RD1-possessing mycobac-
terium cases tested positive for T-SPOT.TB, which was
much higher than those with RD1-negative NTM and
fungal infections (Both 0%) (p = 0.000). The sensitivity in
cutaneous tuberculosis and cutaneous infections of RD1-
possessing NTM were 95.8% and 72.7%, respectively
(p = 0.090) (Table SII 1 ).
The diagnostic performance of the T-SPOT.TB test in
cutaneous infections of RD1-possessing mycobacteria is
shown in Table I. Median SFCs in cutaneous infection of
M. tuberculosis, RD1-possessing NTM, and RD1-negative
NTM before anti-mycobacterium therapy were 23.5 (IQR
10.5–54.0), 14.0 (IQR 6.5–33.8) and 0.0 (IQR 0.0–1.5),
respectively (Fig. S2 1 ) (p = 0.000).
All patients responded well. In the 42 patients (91.3%)
who finished the study, the positive rate decreased from
https://www.medicaljournals.se/acta/content/abstract/10.2340/00015555-3011
1
This is an open access article under the CC BY-NC license. www.medicaljournals.se/acta
Journal Compilation © 2018 Acta Dermato-Venereologica.
doi: 10.2340/00015555-3011
Acta Derm Venereol 2018; 98: 989–990