Parasitic infection may be associated with discordant responses to QuantiFERON and tuberculin skin test in apparently healthy children and adolescents in a tuberculosis endemic setting, Ethiopia

Abstract

Background: M. tuberculosis remains one of the world's deadliest pathogens in part because of its ability to establish persistent, latent infections, which can later reactivate to cause disease. In regions of the globe where disease is endemic, as much as 50% of the population is thought to be latently infected, complicating diagnosis and tuberculosis control. The tools most commonly used for diagnosis of latent M. tuberculosis infection are the tuberculin skin test and the newer interferon-gamma release assays, both of which rely on an antigen-specific memory response as an indicator of infection. It is clear that the two tests, do not always give concordant results, but the factors leading to this are only partially understood.

Methods: In this study we examined 245 healthy school children aged from 12 to 20 years from Addis Ababa, a tuberculosis-endemic region, characterised them with regard to response in the tuberculin skin test and QuantIFERON™ test and assessed factors that might contribute to discordant responses.

Results: Although concordance between the tests was generally fair (90% concordance), there was a subset of children who had a positive QuantIFERON™ result but a negative tuberculin skin test. After analysis of multiple parameters the data suggest that discordance was most strongly associated with the presence of parasites in the stool.

Conclusions: Parasitic gut infections are frequent in most regions where M. tuberculosis is endemic. This study, while preliminary, suggests that the tuberculin skin test should be interpreted with caution where this may be the case.

Figure 1

Association between parasite infestation and TST and QFT-GIT response. The figure shows the study cohort segregated by their response in the TST and QFT-GIT tests and then analyzed for the percentage in each subgroup with a concurrent parasite infestation as identified by stool sampling. The X-axis indicates category of immunodiagnostic test results as (‘-’ = negative and ‘+’ = positive) and the Y-axis indicates the percentage of children with at least one confirmed parasite infection.

Figure 2

Pattern of cytokine mRNA expression among participants segregated according to QFT-GIT and TST results. Data are from whole blood, showing mRNA levels, assessed by qRT-PCR, normalized and expressed relative to the housekeeping gene, human acidic ribosomal protein (HuPo) as fold values. Each point represents the mean of duplicate experiments from a single individual. In both figures, horizontal lines indicate medians and *shows a p-value = 0.0237, ** shows p-values = 0.0035 and 0.0027 for Figure A and B, respectively and *** shows a p-value < 0.0001.

Figure 3

Cytokine mRNA expression pattern among QFT-GIT-positive individuals, without (n = 36) and with concurrent parasitic infestation (n = 15). Data are from whole blood, showing mRNA levels, assessed by qRT-PCR, normalized and expressed relative to the housekeeping gene, human acidic ribosomal protein (HuPo). Empty dots indicate non-parasite infected and filled dots indicate parasite infected individuals. Each point represents the mean of duplicate experiments from a single individual and the median and interquartile values are shown by horizontal lines across the data points for each group.