My patient with rheumatoid arthritis might have been exposed to tuberculosis. Does immunosuppressive therapy affect the results of interferon gamma release assay (IGRA) testing for latent tuberculosis?

The weight of the evidence to date suggests that immunosuppressive therapy, including steroids, other oral immunosuppressants and anti-tumor-necrosis factor (TNF) agents, may negatively impact IGRA results.1

In some ways the finding of false-negative IGRA in the setting of immunosuppression is intuitive since many immunosuppressive agents are potent inhibitors of T cells and interferon-gamma response. 1,2 Despite this, the initial reports have been somewhat conflicting which makes a 2016 meta-analysis of the effect of immunosuppressive therapy on IGRA results in patient with autoimmune diseases (eg, rheumatoid arthritis, lupus, inflammatory bowel disease) particularly timely. 1

This meta-analysis found a significantly lower positive IGRA results among patients on immunosuppressive therapy ( O.R. 0.66, 95% C.I. 0.53-0.83). Breakdown by IGRA test showed a significant association between QuantiFERON-TB Gold In-Tube and lower positive results and a trend toward the same with T-SPOT though the latter did not reach statistical significance with fewer evaluable studies (O.R. 0.81, 95% C.I 0.6-1.1).   Breakdown by type of immunosuppressant showed significantly negative impact of corticossteroids, other oral immunosuppressants, and anti-TNF agents for all. Some studies have reported daily steroid doses as low as 7.5 mg-10 mg may adversely impact T-cell responsiveness in IGRA. 3,4

So, whenever possible, testing for latent TB should be performed before immunosuppressants are initiated.

Bonus Pearl: Did you know that an estimated one-third of the world’s population may have latent TB?

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References

  1. Wong SH, Gao Q, Tsoi KKF, et al. Effect of immunosuppressive therapy on interferon gamma release assay for latent tuberculosis screening in patients with autoimmune diseases: a systematic review and meta-analysis. Thorax 2016;71:64-72. https://thorax.bmj.com/content/thoraxjnl/71/1/64.full.pdf
  2. Sester U, Wilkens H, van Bentum K, et al. Impaired detection of Mycobacterium tuberculosis immunity in patents using high levels of immunosuppressive drugs. Eur Respir J 2009;34:702-10. https://erj.ersjournals.com/content/34/3/702
  3. Kleinert S, Kurzai O, Elias J, et al. Comparison of two interferon-gamma release assays and tuberculin skin test for detecting latent tuberculosis in patients with immune-mediated inflammatory diseases. Ann Rheum Dis 2010;69:782-4. https://ard.bmj.com/content/69/4/782
  4. Ponce de Leon D, Acevedo-Vasquez E, Alvizuri S, et al. Comparison of an interferon-gamma assay with tuberculin skin testing for detection of tuberculosis (TB) infection in patients with rheumatoid arthritis in a TB-endemic population. J Rheumatol 2008;35:776-81. https://www.ncbi.nlm.nih.gov/pubmed/18398944
My patient with rheumatoid arthritis might have been exposed to tuberculosis. Does immunosuppressive therapy affect the results of interferon gamma release assay (IGRA) testing for latent tuberculosis?

Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?

Conventional wisdom has been that in active tuberculosis (TB) patients harbor large numbers of replicating Mycobacterium tuberculosis (Mtb), requiring multiple antibiotics to prevent the emergence of resistant mutants. In contrast, Mtb under latent or “inactive” conditions is presumed to have little capacity for mutation due to reduced bacterial replication, thus generally requiring only one antibiotic for preventive therapy.1

However, the assumption that Mtb has a low capacity for mutation in latent TB due to slow bacterial replication has been challenged in recent years. An experimental study in macaque monkeys with latent Mtb infection using whole genome sequencing demonstrated that despite reduced replication, Mtb acquires a similar number of chromosomal mutations during latency as it does during active infection.1

This finding supports the more current and evolving concept of latent TB which assumes diverse mycobacterial growth states, ranging from complete absence of organisms to actively replicating bacterial populations.2 It also explains why, although effective, isoniazid monotherapy may be a risk factor for the emergence of INH resistance in latent TB. 1,3

 Bonus Pearl: Did you know that INH treatment of latent TB in adults is 60-80% protective when given for 6 months, and 90% protective when given for 9 months? 4

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References

  1. Ford CB, Lin PL, Chase M, et al . Use of whole genome sequencing to estimate the mutation rate of Mycobacterium tuberculosis during latent infection. Nat Genet. 2011;43:482-86. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3101871/
  2. Gideon HP, Flynn JL. Latent tuberculosis: what the host “sees”? Immunol Res 2011;50:202-12. https://www.ncbi.nlm.nih.gov/pubmed/21717066
  3. Balcells ME, Thomas SL, Faussett PG, et al. Isoniazid preventive therapy and risk for resistant tuberculosis. Emerg Infect Dis 2006;12:744-51. https://www.ncbi.nlm.nih.gov/pubmed/16704830
  4. Piccini P, Chiappini E, Tortoli E, et al. Clinical peculiarities of tuberculosis. BMC Infect Dis 2014; 14 (Suppl 1):S4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4015485/

 

Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?