Usefulness of Xpert MTB/RIF and Xpert Ultra to categorize risk of tuberculosis transmission to household contacts

Abstract

Background People with pulmonary tuberculosis (TB) are contagious particularly to their household contacts. Their infectivity has been associated with the bacterial load in sputum samples. This study investigated if the bacterial load in sputum samples as quantified by Xpert MTB/RIF and Xpert Ultra is correlated with the extent latent tuberculosis infection (LTBI) occurred in households contacts of people with pulmonary TB. Methods A retrospective study was performed including people with pulmonary TB presenting at Vall d’Hebron University Hospital, Barcelona between 2011-2021. Their infection ratio, representing the proportion of household members found with LTBI in contact tracing investigation, was compared with the quantitative results of Xpert MTB/RIF and Xpert Ultra using ordinal regression analysis. Results A total of 107 people with pulmonary TB were included. Among their 398 household contacts, 126 (31.7%) cases of LTBI and 14 cases with active TB disease (3.5%) were reported. Higher bacterial load in Xpert MTB/RIF and Xpert Ultra baseline sputum was significantly associated with increased infection ratio’s, providing better estimates than conventional acid-fast bacilli (AFB) smear grading. Conclusion Xpert MTB/RIF and Xpert Ultra could serve as an alternative to the AFB sputum smear grading in determining contact tracing priorities.