A prospective evaluation of a three-gene host response signature to classify tuberculosis severity in children.

Background: Children with non-severe TB may benefit from short-course treatment, but point-of-care tools are needed to stratify disease severity. We prospectively evaluated the Cepheid Xpert MTB-Host Response (HR) prototype cartridge for distinguishing TB severity in children with pulmonary TB (PTB) in The Gambia and Uganda.

Methods: We included children <15 with microbiologically confirmed or clinically diagnosed unconfirmed PTB. Severity was defined using the World Health Organization (WHO) guidelines for a four-month, drug-susceptible regimen. Capillary or venous blood was tested with the HR cartridge for PCR-based detection of three mRNA genes and calculation of a TB score from cycle thresholds. We generated receiver operating characteristic curves with the TB score to classify severe TB and assessed if Xpert-HR could achieve the WHO target accuracy for treatment optimization (≥90% sensitivity, ≥70% specificity).

Results: Among 106 children, the median age was 4 years (IQR 1-7), 56.6% were female, and 13.2% were living with HIV. In all children with PTB, Xpert-HR achieved an AUC of 0.67 (95% CI 0.55-0.78), with 89.3% sensitivity (95% CI 71.8-97.7) and 29.5% specificity (95% CI 19.7-40.9, cut-off≤-0.60). By confirmation status, Xpert-HR approached the target accuracy in children with Confirmed TB, with 62.5% specificity (95% CI 24.5-91.5) at 91.7% sensitivity (95% CI 61.5-99.8, cut-off≤-1.349). Among children with Unconfirmed TB, specificity was lower (24.3% 95% CI 14.8-36.0) at 93.8% sensitivity (95% CI 69.8-99.8, cut-off≤-0.450). Target accuracy was almost achieved in children 5-9 regardless of confirmation status (100% sensitivity [95% CI 71.5-100], 66.7% specificity [95% CI 43.0-85.4], cut-off≤-1.35), but specificity (28.2%, 95% CI 18.6-39.5) was lower for children <5 (92.9% sensitivity [95% CI 76.5-99.1], cut-off≤-0.550).

Conclusions: Xpert-HR approached the target accuracy to stratify PTB severity in older children and those with Confirmed TB but had lower specificity in children with Unconfirmed TB. Child-specific signatures may be needed to improve performance in younger children with paucibacillary disease.