T-cell assay conversions and reversions among household contacts of tuberculosis patients in rural India.
BACKGROUND
Interferon-gamma assays (IGRAs) are alternatives to the tuberculin skin test (TST), but IGRA conversions and reversions are not well understood. In a pilot study, we determined conversions and reversions using QuantiFERON-TB Gold In-Tube((R)) (QFT) among household contacts of TB cases, and evaluated the effect of using various definitions and criteria for conversions.


METHODS
In a cohort of 250 contacts in India, 46% were TST-positive at baseline and 54% were QFT-positive. We re-tested this cohort after 12 months. Conversion rates were estimated using several definitions.


RESULTS
Of the 250 contacts, 205 (82%) underwent repeat testing. Among 85 contacts with baseline TST-negative/QFT-negative results, TST conversion rates ranged between 7.5% and 13.8%, and QFT conversion rates ranged between 11.8% and 21.2%, depending on the definitions used. Among 109 contacts who were QFT-positive at baseline, seven (6.4%) had QFT reversions. QFT reversions were most likely when the baseline TST was negative and QFT results were just above the diagnostic cut-off.


CONCLUSIONS
QFT conversions and reversions occurred among contacts of TB cases. Conversion rates seemed to vary, depending on the test and definitions used for conversions. These findings need to be verified in larger studies in various settings.
Pai
M
M
Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada. madhukar.pai@mcgill.ca
Joshi
R
R
Dogra
S
S
Zwerling
A A
AA
Gajalakshmi
D
D
Goswami
K
K
Reddy
M V R
MV
Kalantri
A
A
Hill
P C
PC
Menzies
D
D
Hopewell
P C
PC
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D004797:Enzyme-Linked Immunosorbent Assay; D005192:Family Health; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011159:Population Surveillance / Q000379:methods*; D012424:Rural Population / Q000706:statistics & numerical data; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000276:immunology*; D014374:Tuberculin Test; D014376:Tuberculosis / Q000276:immunology*; D055815:Young Adult
D007371:Interferon-gamma