1129. The effect of gastrointestinal parasites on interferon-gamma release assays: A cohort study of screening strategies for latent tuberculosis infection in migrants
Session: Oral Abstract Session: Lab Diagnostics
Friday, October 4, 2013: 2:48 PM
Room: The Moscone Center: 300

Background:

Control of tuberculosis (TB) requires prompt identification of active disease and latent TB infection (LTBI). The tuberculin skin test (TST) was the diagnostic method of choice for LTBI, until the development of interferon-gamma release assays (IGRAs). Despite the recognised importance of screening migrants in low-incidence countries for LTBI, there is a lack of operational studies to direct policy. Chronic intestinal helminthic infections are associated with modulation of the host immune response and have previously been associated with indeterminate IGRA results in children.. Study objectives were to assess: 1. A head-to-head comparison of TST with commercial IGRAs in a migrant population from a country of high TB incidence (Nepal) in the UK; 2. Effects of antecedent TST on IGRAS (boosting); 3. Effects of gastrointestinal parasite (GIP) infection on IGRAs.

Methods:

Prospective cohort study of 166 Nepalese military recruits from January 2012 to September 2012.T-SPOT.TB, QFT-GIT and TST were performed at baseline and IGRAs were repeated at 7 days and on completion of LTBI treatment. Stool analysis and serology for GIP infection was undertaken. Statistics: Kaplan concordance and non-parametric data analysis.

Results:

29/166 (17.5%) recruits had a positive IGRA of which 13 (45%) were TST negative. There was good agreement between TST and TSPOT at baseline (κ = 0.67; 95% CI: 0.50-0.85), however poor concordance between IGRAs (κ = 0.52; 95% CI: 0.30-0.74). Following TST, IGRA conversion rates were 9.5% for QFT-GIT (p = 0.0074), 4.2% for T-SPOT.TB (p = 0.87) and IGRA concordance substantial (κ = 0.75: 95% CI: 0.60-0.90). 39/166 (23.5%) recruits had GIP infection. There was a significant increase in mean IFN-g levels between days 0 and 7 in GIP negative vs. GIP positive recruits (p= 0.0067 vs. p = 0.44) (Figure 1). There was a significant negative correlation between hookworm (HW) infection and IGRA positivity (p=0.03) (Figure 2).

Conclusion:

This is a uniquely complete study of LTBI and GIP screening in a migrant population. 1. IGRA concordance was poor at baseline. 2. The QFT-GIT is boosted by antecedent TST that results in comparable agreement between IGRAs. 3. Gastrointestinal parasitic infection has a confounding effect on IGRA results.  

Figure 1:

Figure 2:

Matthew O'shea, MD, The Jenner Institute, University of Oxford, Oxford, United Kingdom, Tom Fletcher, MD, Liverpool School Tropical Medicine, Liverpool, United Kingdom, Adam Cunningham, PhD, School of Immunity and Infection, University of Birmingham, Birmingham, United Kingdom, Helen Mcshane, MD PhD, Oxford University, Oxford, United Kingdom; University of Oxford, Oxford, United Kingdom, David Spence, MD, Dept of Respiratory Medicine, Friarage Hospital, North Yorshire, United Kingdom, Wendi Bailey, PhD, Diagnostic Laboratory, Liverpool School of Tropical Medicine, Liverpool, United Kingdom, Nicholas Beeching, MD, Liverpool School of Tropical Medicine, Liverpool, United Kingdom and Duncan Wilson, MD, Medical Directorate, Royal Centre for Defence Medicine (Academia and Research), Birmingham, United Kingdom

Disclosures:

M. O'shea, None

T. Fletcher, None

A. Cunningham, None

H. Mcshane, None

D. Spence, None

W. Bailey, None

N. Beeching, None

D. Wilson, None

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