Comparing Interferon- Release Assay with Tuberculin Skin Test Readings at 48-72 Hours and 144-168 Hours with Use of 2 Commercial Reagents

Changes in tuberculin skin test positivity over 20 years in periurban shantytowns in Lima, Peru

A cross-sectional, community-based study was performed in 2012 with 428 residents of periurban shantytowns in Lima, Peru to study risk factors for and changes in latent tuberculosis infection in age-stratified groups compared with our data from the same region in 1990 (N = 219) and 2005 (N = 103). Tuberculin skin test positivity in these communities was highly prevalent at 52% overall, increased with age (P < 0.01) and was similar to 2005 (53%) and 1990 (48%). From 1990 to 2012, the prevalence of tuberculin positivity decreased in 5-14 and 15-24 year old groups (to 17% and 34%, respectively, both P < 0.05). However, this may be explained by cessation of Bacille Calmette-Guérin revaccination during this period, because Bacille Calmette-Guérin revaccination doubled tuberculin positivity. Over the same 22-year period, tuberculin positivity in the ≥ 25 year old group remained high (71%, P = 0.3), suggesting that prevalent latent tuberculosis infection persists in the adult population despite improving medical care and socioeconomic development in this region.

The effects of HIV on the sensitivity of a whole blood IFN-gamma release assay in Zambian adults with active tuberculosis

BACKGROUND

Interferon gamma release assays (IGRA) are replacing the tuberculin skin test (TST) as a diagnostic tool for Mycobacterium tuberculosis infection. However research into the test's performance in the high HIV-TB burden setting is scarce. This study aimed to define the sensitivity of an IGRA, QuantiFERON-TB Gold In-Tube (QGIT), in adult Zambian patients with active smear-positive tuberculosis. Secondary outcomes focussed on the effect of HIV on the test's performance.

PRINCIPAL FINDINGS

Patients attending government health clinics were recruited within 1 month of starting treatment for TB. Subjects were tested with QGIT and TST. T lymphocyte counts were estimated (CD3(+), CD4(+), CD8(+)). QGIT was performed for 112 subjects. 83/112 were QGIT positive giving an overall sensitivity of 74% [95%CI: 66,82]. A marked decrease in sensitivity was observed in HIV positive patients with 37/59 (63%) being QGIT positive compared to 31/37 (84%) HIV negative patients [chi(2) p = 0.033]. Low CD4(+) count was associated with increases in both indeterminate and false-negative results. Low CD4(+) count in combination with high/normal CD8(+) count was associated with false-negative results. TST was recorded for 92 patients, 62/92 were positive, giving a sensitivity of 67% [95%CI: 58,77]. Although there was little difference in the overall sensitivities, agreement between TST and QGIT was poor.

CONCLUSIONS

QGIT was technically feasible with results in HIV negative subjects comparable to those achieved elsewhere. However, where under-treated HIV is prevalent, an increased proportion of both indeterminate and false-negative QGIT results can be expected in patients with active TB. The implications of this for the diagnosis of LTBI by QGIT is unclear. The diagnostic and prognostic relevance of IGRAs in high burden settings needs to be better characterised.

Increase in tuberculin skin test converters among health care workers after a change from Tubersol to Aplisol

BACKGROUND

Comparability of the 2 commercially available tuberculin skin testing (TST) preparations, Aplisol (Parkdale Pharmaceuticals, Inc, Rochester, MI) and Tubersol (Aventis Pasteur, Inc, Swiftwater, PA), remains uncertain, particularly in groups that undergo repeated testing, such as health care workers.

METHODS

Data from the annual tuberculosis screening program for health care workers at the Kennedy Krieger Institute in Baltimore, Maryland, were analyzed. Conversion rates during 1997-2003 in workers screened with Tubersol (n = 8897 screenings) were compared with 1203 workers who underwent screening with Aplisol in 2004. Repeat testing with Tubersol was examined in those who converted in 2004 with Aplisol.

RESULTS

Annual TST conversion rates ranged from 0.3% to 0.9% between 1997 and 2003 using Tubersol. After switching to Aplisol in 2004, the TST conversion rate significantly increased to 2% (P < .001). Among 24 health care workers who were converters with Aplisol in 2004, only 6 of 23 (26%) were converters on repeat testing with Tubersol (1 declined retesting). None of the apparent converters (n = 24) had radiographic evidence of Mycobacterium tuberculosis infection, and there was no epidemiologic evidence of transmission. Reclassification based on Tubersol testing in 2004 resulted in conversion rates comparable with previous years.

CONCLUSION

We conclude that the change from Tubersol to Aplisol resulted in falsely elevated conversion rates. Our results support the guidelines from the Centers for Disease Control and Prevention recommendations that 1 product should be used consistently in populations undergoing periodic testing.