Spatial Analysis of Drug-Susceptible and Multidrug-Resistant Cases of Tuberculosis, Ho Chi Minh City, Vietnam, 2020-2023.

We characterized the spatial distribution of drug-susceptible (DS) and multidrug-resistant (MDR) tuberculosis (TB) cases in Ho Chi Minh City, Vietnam, a major metropolis in southeastern Asia, and explored demographic and socioeconomic factors associated with local TB burden. Hot spots of DS and MDR TB incidence were observed in the central parts of Ho Chi Minh City, and substantial heterogeneity was observed across wards. Positive spatial autocorrelation was observed for both DS TB and MDR TB. Ward-level TB incidence was associated with HIV prevalence and the male proportion of the population. No ward-level demographic and socioeconomic indicators were associated with MDR TB case count relative to total TB case count. Our findings might inform spatially targeted TB control strategies and provide insights for generating hypotheses about the nature of the relationship between DS and MDR TB in Ho Chi Minh City and the wider southeastern region of Asia.

Species sampling has a major impact on phylogenetic inference.

Representative properties of gnathostome species of a rich 28S rRNA data base were studied through the analysis of the fluctuations they provoked in bootstrap proportions (BPs) of nodes of parsimonious trees. Using original programs which permit BP comparison between different trees, it is empirically demonstrated that 4- to 24-species-trees are highly sensitive to species sampling: the inferences obtained from subsets of 4, 8, 16, or 24 species are not congruent with the whole set of 31 species. Study of trees obtained from exhaustively sampling all combinations of single species taken from each presumed monophyletic group shows precisely the impact of each species on the BP of each node. This procedure also shows that the impact of species changes within a given group on tree BPs is localized to its two or three neighboring nodes. The observation of differing impacts of species emphasizes the importance of sampling several species per presumed monophyletic group. It is also concluded that it is necessary to sample several successive outgroups and that the impact of a species on BPs depends mainly on the sampling context. Before undertaking extensive sequencing, the impact of species should be more often considered, since its effect on BPs is stronger than previously thought.

How many nucleotides are required to resolve a phylogenetic problem? The use of a new statistical method applicable to available sequences.

The evolution of bootstrap proportions (BP) with sequence length was studied using a 28S ribosomal RNA data set. For different sequence lengths, informative sites were jackknifed several times. Bootstrapping was subsequently performed on each of these subsamples. For each node, BPs so obtained were plotted against sequence length, showing the evolution of the robustness with increasing number of informative sites. For robust nodes (BP of 100%), the pattern of BPs is unvarying and is described by a simple function BP = 100 (1-e-b(x-x')), where x is the number of informative sites and b and x' are two parameters estimated using a nonlinear regression procedure. When a node has a BP < 100% and the pattern of BPs fits this function, it is possible to estimate the number of informative sites required to obtain a given average BP. The method also identifies nonrobust nodes (nonascending clusters of BP dots), for which it seems to be more cost effective and fruitful to turn to other species and/or genes rather than to continue sequencing longer gene lengths from the same species to reach a BP of 95%.