Mucosal-associated invariant T lymphocytes (MAIT lymphocytes) are characterized by two evolutionarily conserved features: an invariant T cell antigen receptor (TCR) alpha-chain and restriction by the major histocompatibility complex (MHC)-related protein MR1. Here we show that MAIT cells were activated by cells infected with various strains of bacteria and yeast, but not cells infected with virus, in both humans and mice. This activation required cognate interaction between the invariant TCR and MR1, which can present a bacteria-derived ligand. In humans, we observed considerably fewer MAIT cells in blood from patients with bacterial infections such as tuberculosis. In the mouse, MAIT cells protected against infection by Mycobacterium abscessus or Escherichia coli. Thus, MAIT cells are evolutionarily conserved innate-like lymphocytes that sense and help fight off microbial infection.

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Microsporidiosis cases due to Enterocytozoon bieneusi and Encephalitozoon intestinalis are emerging opportunistic infections associated with a wide range of clinical syndromes in humans. The aim of this study was to specify microsporidial epidemiology in two different geographical areas. From November 2004 to August 2005, 228 and 42 stool samples were collected in Niamey, Niger, and Hanoi, Vietnam, respectively. Screening for microsporidia was performed using UV-light microscopy. Detection was confirmed by molecular biology using two methods specific for E. bieneusi and E. intestinalis. All samples positive for E. bieneusi were subjected to genotyping. In this study, we found high prevalences of microsporidiosis among human immunodeficiency virus-infected patients, 10.5% and 9.5%, respectively, in Niamey and Hanoi. These levels of prevalence are similar to those recorded in European countries before highly active antiretroviral therapy was introduced. In the samples positive for E. bieneusi, we found seven distinct genotypes, including two genotypes not previously described. The E. bieneusi genotype distributions in the two geographical areas suggest different routes of infection transmission, person-to-person in Niger and zoonotic in Vietnam.

Background The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men.