Bacterial resistance represents a growing threat to public health, especially with the dissemination of genes such as blaNDM (New Delhi Metallo-β-lactamase), which confers resistance to nearly all β-lactams, including carbapenems. In Brazil, recurrent use of the acronym “NDN” (not determined/not detected/not available) has been observed in laboratory reports, often masking the presence of resistance mechanisms due to diagnostic limitations. This study aims to discuss the impact of limited genotypic surveillance and to present resistance data from Minas Gerais that demonstrate the circulation of critical genes such as blaNDM. This is a cross-sectional, retrospective, and descriptive study that analyzed 13, 012 Gram-negative bacterial isolates from hospitals in Minas Gerais between 2016 and 2022. Urine, blood, tracheal secretion, and surgical wound exudate samples were selected and referred to the laboratory based on phenotypic resistance profiles. Genotypic detection was performed by PCR for the genes blaKPC, blaOXA, blaNDM, blaSPM, blaVIM, and blaIMP. Data were categorized into three periods: pre-pandemic, pandemic, and post-pandemic COVID-19. The analysis revealed a significant increase in the frequency of blaNDM and blaOXA genes in the post-pandemic period, indicating expansion of resistant strains following diagnostic service disruptions and intensive antimicrobial use during the pandemic. Although blaKPC showed a proportional decrease, its absolute number increased. The mcr-1 gene, related to colistin resistance, was identified in four isolates in the post-pandemic period, an unprecedented finding in the analyzed context. The use of “NDN” in laboratory contexts does not represent absence of resistance, but rather absence of detection capacity, creating a false scenario of control. The lack of genotypic surveillance compromises control actions, diagnosis, and treatment. These findings reinforce the urgent need for investment in diagnostic infrastructure, integration of surveillance systems, and expansion of access to molecular testing, especially in regions outside major urban centers.
Pereira et al. (2026) studied this question.