Tuberculosis in a Swiss army training camp: contact investigation using an Interferon gamma release assay.
BACKGROUND
In tuberculosis (TB), the risk of exposure is determined mainly by the proximity to and the hours of direct contact with an infectious patient. We describe the contact investigation after detection of an infectious form of TB in a military camp using an Interferon-g-Release-Assay (IGRA, QuantiFERON-TB Gold In Tube [QTF-GIT]) eight weeks after detection of the index case. INDEX PATIENT: The index patient presented with fever, cough and weight loss in the military hospital six weeks after entering the camp. TB was suspected and anti-tuberculous therapy given immediately. Subsequently, TB was microbiologically confirmed.


METHODS
Four exposure groups were formed a priori based on the proximity and the hours of direct contact to the index case. 168 (95.5%) agreed to be investigated: - Group A: sharing the same dormitory (15 persons) - Group B: same platoon, but not sharing the dormitory (20 persons) - Group C: staff and patients of the military hospital (22 persons) - Group D: other three platoons and senior military staff (111 persons).


RESULTS
34 (20.2%) out of 168 contacts tested positive in the QFT-GIT assay. For the exposure groups, the respective QFT-GIT testing results were: group A, 14/15 (93%); group B, 4/20 (20%); group C, 5/22 (22.7%); and group D, 11/111 (9.9%). No secondary TB cases were identified.


CONCLUSIONS
In our study, test results show a correlation with the risk of exposure, suggesting that IGRA may be useful for the assessment of TB infection in TB contacts. The high mobility of recruits reduced traceability of contacts. In this context, QFT-GIT allowed for an efficient screening of contacts at a single time point.
Kipfer
Beat
B
Regional Military Medical Unit, Thun, Switzerland. bkipfer@mac.com
Reichmuth
Markus
M
Büchler
Markus
M
Meisels
Cyrus
C
Bodmer
Thomas
T
D000328:Adult; D000942:Antigens, Bacterial / Q000276:immunology; D000995:Antitubercular Agents / Q000627:therapeutic use; D001500:BCG Vaccine / Q000276:immunology; D001426:Bacterial Proteins / Q000276:immunology; D001681:Biological Assay; D015331:Cohort Studies; D016358:Contact Tracing / Q000379:methods*; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D008262:Macrophage Activation / Q000276:immunology; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data*; D010446:Peptide Fragments / Q000276:immunology; D011237:Predictive Value of Tests; D013557:Switzerland; D013601:T-Lymphocytes / Q000276:immunology*; D014057:Tomography, X-Ray Computed; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis / Q000276:immunology / Q000517:prevention & control / Q000635:transmission*
D000942:Antigens, Bacterial; D000995:Antitubercular Agents; D001500:BCG Vaccine; D001426:Bacterial Proteins; C489634:CFP-10 protein (71-85), Mycobacterium tuberculosis; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D010446:Peptide Fragments; C072681:Mycobacterium tuberculosis antigens; D007371:Interferon-gamma