Each individual is provided with a unique gut microbiota profile that plays many specific functions in host nutrient metabolism, maintenance of structural integrity of the gut mucosal barrier, immunomodulation, and protection against pathogens. Gut microbiota are composed of different bacteria species taxonomically classified by genus, family, order, and phyla. Each human’s gut microbiota are shaped in early life as their composition depends on infant transitions (birth gestational date, type of delivery, methods of milk feeding, weaning period) and external factors such as antibiotic use. These personal and healthy core native microbiota remain relatively stable in adulthood but differ between individuals due to enterotypes, body mass index (BMI) level, exercise frequency, lifestyle, and cultural and dietary habits. Accordingly, there is not a unique optimal gut microbiota composition since it is different for each individual. However, a healthy host–microorganism balance must be respected in order to optimally perform metabolic and immune functions and prevent disease development. This review will provide an overview of the studies that focus on gut microbiota balances in the same individual and between individuals and highlight the close mutualistic relationship between gut microbiota variations and diseases. Indeed, dysbiosis of gut microbiota is associated not only with intestinal disorders but also with numerous extra-intestinal diseases such as metabolic and neurological disorders. Understanding the cause or consequence of these gut microbiota balances in health and disease and how to maintain or restore a healthy gut microbiota composition should be useful in developing promising therapeutic interventions.

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The aim of the present study was to describe the clinical presentation of patients aged ≥80 years with coronavirus disease 2019 , and provide insights regarding the prognostic factors and the risk stratification in this population.Methods: This was a single-center, retrospective, observational study, carried out in a referral center for COVID-19 in central Italy. We reviewed the clinical records of patients consecutively admitted for confirmed COVID-19 over a 1-month period (1-31 March 2020). We excluded asymptomatic discharged patients. We identified risk factors for death, by a uni-and multivariate Cox regression analysis. To improve model fitting and hazard estimation, continuous parameters where dichotomized by using Youden's index.Results: Overall, 69 patients, aged 80-98 years, met the inclusion criteria and were included in the study cohort. The median age was 84 years (82-89 years is interquartile range); 37 patients (53.6%) were men. Globally, 14 patients (20.3%) presented a mild, 30 (43.5%) a severe and 25 (36.2%) a critical COVID-19 disease. A total of 23 (33.3%) patients had died at 30 days' follow up. Multivariate Cox regression analysis showed that severe dementia, pO 2 ≤90 at admission and lactate dehydrogenase >464 U/L were independent risk factors for death. Conclusions:The present data suggest that risk of death could be not age dependent in patients aged ≥80 years, whereas severe dementia emerged is a relevant risk factor in this population. Severe COVID-19, as expressed by elevated lactate dehydrogenase and low oxygen saturation at emergency department admission, is associated with a rapid progression to death in these patients.