Latent tuberculosis infection in travelers: is there a role for screening using interferon-gamma release assays?

Screening travellers to high-endemic countries for infection with Mycobacterium tuberculosis using interferon gamma release assay; a prospective study

Background

International travel from low-incidence to high-incidence countries for tuberculosis (TB) is regarded as a risk factor for acquiring TB infection. In this prospective study among long-term travellers we examined the incidence of TB infection using Interferon gamma release assay (IGRA) test and compared these data with results from a visit to the TB department to which all long-term travellers were routinely referred.

Methods

Immunocompetent adults, travelling for 13–52 weeks to TB-endemic countries, donated blood pre- and post-travel for IGRA. The pre-travel IGRA was only tested in case of a positive IGRA post-travel. Results from their visit(s) to the TB department for TST pre- and post-travel were collected and compared with study results.

Results

We found two IGRA conversions in a group of 516 travellers, resulting in an attack rate (AR) of 0.4% (95% CI: 0.5 - 13.9) and an incidence rate (IR) of 0.85 per 1000 person-months (95% CI: 0.1-3.1).

We found 5 tuberculin skin test (TST) conversions, resulting in AR of 1.9% (5/261; 95% CI: 0.6 - 4.4) and an IR of 4.26 per 1000 person-months (95% CI: 1.38- 9.94). In our study these converters all had a negative IGRA. One traveller however, who was retested later at the TB department due to a positive TST, then appeared to have seroconverted.

Conclusions

The risk of long-term travellers among our study population acquiring TB infection is low. We conclude that post-travel IGRA alone could be used for screening for TB infection among long-term travellers to high-endemic TB countries, but preferably not earlier than 8 weeks after return. One might even argue that IGRA testing should be limited to only those travellers who are going to work in a medical setting. A person with a positive IGRA should be referred to a TB physician for further evaluation.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2334-14-515) contains supplementary material, which is available to authorized users.

Expatriates: special considerations in pretravel preparation

Expatriates comprise a diverse set of travelers who face unique medical, psychiatric, and non-health-related risks as a result of increased exposure to host country environment and associated lifestyle. Expatriates have an increased risk of developing malaria, gastrointestinal disorders, latent tuberculosis, vaccine-preventable infections, and psychological disorders, when compared with other travelers, yet the majority of existing pretravel guidelines have been designed to suit the needs of nonexpatriates. Although greater interest in expatriate health issues has led to improved characterization of illness in this population, expatriate-specific risk mitigation strategies-including modifications to chemoprophylaxis recommendations, limiting tuberculosis exposure, and prevention of occupational or sexual blood-borne virus transmission-are poorly described. Occupations and destinations affect travel-related disease risk and should inform the pretravel consultation.

Retesting for latent tuberculosis in patients with inflammatory bowel disease treated with TNF-α inhibitors

BACKGROUND

Patients treated with TNF-α inhibitors (TNFi) are at high risk of reactivation of latent tuberculosis (LTB). Prospective studies on monitoring of TB reactivation and/or infection in this risk group are lacking.

AIM

To test the conversion and reversion rate of screening tests for latent TB serial tuberculin skin test (TST) and interferon-γ release assay (IGRA) under ongoing TNFi therapy.

METHODS

We retested consecutive patients with IBD receiving TNFi therapy for a minimum of 5 months for LTB using IGRA and TST. A detailed patient history and concomitant therapy were recorded for each subject.

RESULTS

After a median of 34.9 weeks (20.7–177.7), IGRA was retested in 184/227 patients (81.1%; Crohn's disease n = 139, ulcerative colitis n = 45) still under index TNFi. TST was available in 144/184 subjects (78.2%). The majority of patients were TNFi naïve (147/184, 79.9%). In a subgroup of patients who received isoniazid due to diagnosis of latent TB at baseline (n = 32), 6/13 patients (46.2%) with baseline positive IGRA and 3/22 patients (13.6%) with baseline positive TST reverted to negative at retesting. In patients without diagnosis of LTB at baseline no permanent IGRA conversion was observed, but there were 6/144 (4.2%) TST conversions from negative to positive. No single case of TB reactivation or infection was recorded during the observation period.

CONCLUSIONS

During treatment TNF-α inhibitors conversion was observed for tuberculin skin test, but not interferon-γ release assay. As compared with tuberculin skin test, interferon-γ release assay reverted in nearly half of isoniazid-treated patients for latent tuberculosis. However, the fact that patients in whom the interferon-γ release assay test result remained positive did not develop active tuberculosis during follow-up questions the utility of interferon-γ release assay as a monitoring tool during chemoprevention.