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We established a new reversed phase-high performance liquid chromatography method combined with electrospray ionization quadrupole time-of-flight tandem mass spectrometry for the simultaneous determination and structural characterization of different lipid A types in bacteria (Escherichia coli O111, Salmonella adelaide O35 and Proteus morganii O34) showing serological cross-reactivity. The complex lipid A mixtures (obtained by simple extraction and acid hydrolysis of the outer membrane lipopolysaccharides) were separated and detected without phosphate derivatization. Several previously unidentified ions were detected, which differed in the number and type of acyl chains and number of phosphate groups. In several cases, we observed the different retention of isobaric lipid A species, which had different secondary fatty acyl distribution at the C2' or the C3' sites. The fragmentation of the various, C4' monophosphorylated lipid A species in deprotonated forms provided structural assignment for each component. Fragmentation pathways of the tri-acylated, tetra-acylated, penta-acylated, hexa-acylated and hepta-acylated lipid A components and of the lipid A partial structures are suggested. As standards, the hexa-acylated ion at m/z 1716 with the E. coli-type acyl distribution and the hepta-acylated ion at m/z 1954 with the Salmonella-type acyl distribution were used. The results confirmed the presence of multiple forms of lipid A in all strains analyzed. In addition, the negative-ion mode MS permitted efficient detection for non-phosphorylated lipid A components, too. Copyright © 2016 John Wiley & Sons, Ltd.

Dear Editor, Coronavirus Disease 2019 (COVID-19) is a viral infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with a mortality rate of 3-7% [1]. The high mortality results from fulminant pneumonia leading to acute respiratory distress syndrome and multiple organ failure [2, 3]. Initial reports suggest that comorbidities cause a more severe course of infection and a poorer prognosis [4, 5]. Considering the fast spread and high mortality of COVID-19, it is necessary to understand the possible risk factors affecting its progression. We aimed to perform a systematic search to evaluate the potential role of all reported comorbidities on the disease course. Details of our report are provided in Supplementary file 1. We searched MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Scopus between 01/01/2020 and 05/11/2020. The main outcomes were mortality, intensive care unit (ICU) admission and severity. Definitions of the investigated outcomes are available in Supplementary file 2, Table 2. Odds ratios (OR) with 95% confidence intervals (CI) were calculated to objectify the association between comorbidities and the outcomes by the random-effects model. The study was registered on PROSPERO (CRD42020176781). Of 33,987 records screened, 61 cohort studies with 31,089 (median 162; IQR: 103-338) patients were included in the meta-analysis. The overall mortality rate was 10.0%, 19.9% of patients needed intensive, while the reported severity was 24.0%. Underlying chronic

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