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K13 appears to be a major determinant of artemisinin resistance throughout Southeast Asia. While we found some evidence of spreading resistance, there was no evidence of resistance moving westward from Cambodia into Myanmar.

Mortality from coronavirus disease 2019 (COVID-19) is strongly associated with cardiovascular disease, diabetes, and hypertension. These disorders share underlying pathophysiology related to the renin-angiotensin system (RAS) that may be clinically insightful. In particular, activity of the angiotensin-converting enzyme 2 (ACE2) is dysregulated in cardiovascular disease, and this enzyme is used by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to initiate the infection. Cardiovascular disease and pharmacologic RAS inhibition both increase ACE2 levels, which may increase the virulence of SARS-CoV-2 within the lung and heart. Conversely, mechanistic evidence from related coronaviruses suggests that SARS-CoV-2 infection may downregulate ACE2, leading to toxic overaccumulation of angiotensin II that induces acute respiratory distress syndrome and fulminant myocarditis. RAS inhibition could mitigate this effect. With conflicting mechanistic evidence, we propose key clinical research priorities necessary to clarify the role of RAS inhibition in COVID-19 mortality that could be rapidly addressed by the international research community.

BACKGROUND Drug-resistant tuberculosis threatens recent gains in the treatment of tuberculosis and human immunodeficiency virus (HIV) infection worldwide. A widespread epidemic of extensively drug-resistant (XDR) tuberculosis is occurring in South Africa, where cases have increased substantially since 2002. The factors driving this rapid increase have not been fully elucidated, but such knowledge is needed to guide public health interventions. METHODS We conducted a prospective study involving 404 participants in KwaZulu-Natal Province, South Africa, with a diagnosis of XDR tuberculosis between 2011 and 2014. Interviews and medical-record reviews were used to elicit information on the participants’ history of tuberculosis and HIV infection, hospitalizations, and social networks. Mycobacterium tuberculosis isolates underwent insertion sequence (IS)6110 restriction-fragment– length polymorphism analysis, targeted gene sequencing, and whole-genome sequencing. We used clinical and genotypic case definitions to calculate the proportion of cases of XDR tuberculosis that were due to inadequate treatment of multidrug-resistant (MDR) tuberculosis (i.e., acquired resistance) versus those that were due to transmission (i.e., transmitted resistance). We used social-network analysis to identify community and hospital locations of transmission. RESULTS Of the 404 participants, 311 (77%) had HIV infection; the median CD4+ count was 340 cells per cubic millimeter (interquartile range, 117 to 431). A total of 280 participants (69%) had never received treatment for MDR tuberculosis. Genotypic analysis in 386 participants revealed that 323 (84%) belonged to 1 of 31 clusters. Clusters ranged from 2 to 14 participants, except for 1 large cluster of 212 participants (55%) with a LAM4/KZN strain. Person-to-person or hospital-based epidemiologic links were identified in 123 of 404 participants (30%). CONCLUSIONS The majority of cases of XDR tuberculosis in KwaZulu-Natal, South Africa, an area with a high tuberculosis burden, were probably due to transmission rather than to inadequate treatment of MDR tuberculosis. These data suggest that control of the epidemic of drug-resistant tuberculosis requires an increased focus on interrupting transmission. (Funded by the National Institute of Allergy and Infectious Diseases and others.)

Repeated emergence, not international dissemination, is behind the rise of multidrug-resistant lineage 4 tuberculosis.

Investigators. Genetic determinants of response to clopidogrel and cardiovascular events.

We investigated the effects of elevated O2 pressure on the production of O2 by photosynthetic organisms in several species of plants, algae, and a cyanobacterium. Using a non-invasive fluorometry technique to monitor sequential turnover of the Photosystem II (PSII) reaction center as a function of O2 pressures, we showed that none of the reactions of water oxidation are affected by elevated O2 pressures up to 50-fold greater than atmospheric conditions. Thus, the terminal step of O2 release from the water oxidation complex (S4 → S0 + O2 + nH+) is not reversible in whole cells, leaves, or isolated thylakoid membranes containing PSII, in contrast to reports using detergent-extracted PSII complexes. This implies that there is no thermodynamically accessible intermediate that can be populated by preventing or reversing the O2 release step with atmospheric O2. To assess the sensitivity of PSII charge recombination to O2 pressure we quantitatively modeled the consequences of two putative perturbations to the catalytic cycle of water oxidation within the framework of the Kok model. Based on the breadth of oxygenic phototrophs examined in this study, we conclude that O2 accumulation in cells or the atmosphere does not suppress photosynthetic productivity through the reversal of water oxidation in contemporary phototrophs, and would have been unlikely to influence the evolution of oxygenic photosynthesis.

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