In a recent publication in the International Journal of Infectious Diseases, researchers sought to approximate the pooled percentage of extensively drug–resistant tuberculosis (XDR-TB) and pre-extensively drug–resistant tuberculosis (pre-XDR-TB) in patients with multidrug-resistant TB (MDR-TB).

The researchers conducted a systematic review of 64 observational studies examining XDR-TB or pre-XDR-TB in patients with MDR-TB. The studies were identified from articles published in English retrieved in the Google Scholar, ScienceDirect, and PubMed databases and gray literature through July 2022.

The study population involved 12,711 individuals from 22 countries across World Health Organization (WHO) regions, including India, China, Southeast Asia, Africa, Western Pacific, Europe, North and South America, and the Eastern Mediterranean who were treated from 2003 to 2020 (publication 2008-2021).

The results revealed that the overall estimated pooled percentage of XDR-TB in patients with MDR-TB was 9%. By countries, the lowest percentage of XDR-TB was in Ethiopia (1%) and Cameroon (1%), and the greatest was in India (77%). By WHO regions, pooled percentage of XDR-TB was Eastern Mediterranean regions (3%), African regions (3%), Americas (6%), Southeast Asian regions (10%), and Western Pacific (12%). The pooled percentage of XDR-TB among new MDR-TB patients was 3%, and, in previously treated cases, it was 6%.

The overall pooled percentage of pre-XDR-TB among MDR-TB cases was 26%. By countries, the lowest percentage of pre-XDR-TB was in Ethiopia (3%), and the highest percentage was in China (66%). By WHO regions, pooled percentage of pre-XDR-TB was African regions (12%), Americas (14%), European regions (22%), Eastern Mediterranean (30%), Southeast Asia (32%), and Western Pacific, 35%. The pooled percentage of pre-XDR-TB in new MDR-TB patients was 9%, and, in previously treated cases, it was 13%.

With regard to results, the authors wrote, "The pooled proportion of pre-XDR-TB was 26% (95% CI: 22%-31%), whereas XDR-TB in MDR-TB cases was 9% (95% CI: 7%-11%) in patients treated for MDR-TB. The pooled proportion of fluoroquinolone resistance was 27% (95% CI: 22-33%), and second-line injectable drugs was 11% (95% CI: 9-13%). Whereas the pooled resistance proportions to bedaquiline, clofazimine, delamanid, and linezolid were 5% (95% CI: 1-8%), 4% (95% CI: 0-10%), 5% (95% CI; 2-8%), and 4% (95% CI: 2-10%), respectively."

The limitations of the review and meta-analysis noted by the authors were that publications in this study were published only in English and most studies reported on the Southeast Asian and Western Pacific regions of WHO.

The authors concluded that the current review study demonstrated the presence of a higher percentage of pre-XDR-TB and XDR-TB than the WHO estimates, and the most significant percentages of pre-XDR-TB and XDR-TB were detected in the Western Pacific and Southeast Asian regions.

They also noted that a significant percentage of resistance to new drugs was also detected, and programmatic interventions are necessary to decrease the incidence of pre-XDR-TB and XDR-TB.

Lastly, they wrote, "Countries should implement robust passive or active surveillance of DR-TB to understand the current burden of resistance to second-line and newly introduced drugs."

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