Impact of SARS-CoV-2 viral load and duration of symptoms before hospital admission on the mortality of hospitalized COVID-19 patients

Purpose

Assess the impact of viral load estimated by cycle threshold (Ct) of reverse transcription real time-polymerase chain reaction (rRT-PCR) and the days from symptoms onset on mortality in hospitalized patients with COVID19.

Methods

Retrospective observational study of 782 patients with a positive rRT-PCR from a nasopharyngeal swab was performed within the first 24 h from admission. Demographic data, clinical manifestations and laboratory parameters were collected. Uni- and multivariate analyses were performed to identify factors associated with mortality at 60 days.

Results

Ct was divided into three groups and the mortality rate decreased from 27.3 to 20.7% and 9.8% for Ct values of ≤ 20, 21–25 and > 25, respectively (P = 0.0001). The multivariate analysis identified as predictors of mortality, a Ct value < 20 (OR 3.13, CI 95% 1.38–7.10), between 21–25 (OR 2.47, CI 95% 1.32–4.64) with respect to a Ct value > 25. Days from symptoms onset is a variable associated with mortality as well (DSOA) ≤ 6 (OR 1.86, CI 95% 1.00–3.46), among other factors. Patients requiring hospital admission within 6 DSOA with a Ct value ≤ 25 had the highest mortality rate (28%).

Conclusions

The inclusion of Ct values and DSOA in the characterization of study populations could be a useful tool to evaluate the efficacy of antivirals.

[Update on Ebola virus infection]

Ebola virus disease became a major global public health concern after the last outbreak originated in West Africa in 2014. The epidemic has affected 10 countries in 3 continents, with an estimated global mortality of 41%, highlighting how a disease known to be restricted to the African continent can affect directly or indirectly many countries in the world. In this work, we review different aspects of the virus, the disease and the current outbreak.

Aetiology of traveller's diarrhoea: evaluation of a multiplex PCR tool to detect different enteropathogens

Traveller's diarrhoea (TD) is the most common illness reported in international travellers. TD is caused by a wide range of pathogens, including bacteria, viruses and parasites. Multiplex PCR assays can be especially useful for studying the aetiology of TD. The first objective of this study was to evaluate the utility of the commercially available multiplex PCR (xTAG(®) Gastrointestinal Pathogen Panel (GPP)) for the diagnosis of TD. A total of 185 stool specimens obtained from 174 patients were processed using the GPP assay. This test detected 86 pathogens in 67 stool samples (67/185, 36.2%). Sixteen pathogens out of 86 were also detected by routine testing. The remaining pathogens (n = 70) required further confirmation by alternative techniques. Finally, 60 out of 70 pathogens were confirmed. The second objective of this study was to analyse the aetiology of TD based on the results obtained by the GPP test and routine methods. The primary pathogens causing TD were Shigella (24.2%) followed by enterotoxigenic Escherichia coli (ETEC) (23.2%), enteroaggregative E. coli (14.7%) and Giardia (13.7%). Significant regional differences were observed for ETEC with 19.4% of TD cases acquired in Africa, 11.3% in Asia and none in South Central (SC) America (p 0.01), Giardia was found in 1.5% of cases among those who had travelled to Africa, 14.1% of those who had travelled to Asia and 3% of those who had travelled to SC America (p 0.01). In conclusion, the GPP test improved the detection of enteropathogens and allowed better assessment of the aetiology of TD.

Signals through 4-1BB are costimulatory to previously activated splenic T cells and inhibit activation-induced cell death

Previously, we and others showed that signals relayed through the murine T cell Ag 4-1BB enhance primary T cell responses, and that blocking the interaction of 4-1BB with its ligand results in decreased responses to polyclonal activators and to alloantigens. Because 4-1BB expression is induced following primary stimulation, we investigated the role of signaling through this molecule in the reactivation of proliferating T cells. To this end, preactivated, 4-1BB-expressing T cells were restimulated in the presence of plate-immobilized mAbs directed against 4-1BB or the prototypic costimulatory molecule CD28. In this work, we show that in the presence of either signal, T cells respond to TCR cross-linking with strong proliferative responses and cytokine production; moreover, our findings indicate that T cell proliferation partially correlates with surface 4-1BB expression. In addition, our results suggest that Ab-mediated costimulatory signals can act independently of potential accessory B7-CD28/CTLA-4 (cytotoxic T lymphocyte Ag-4) interactions. Importantly, the characteristic DNA fragmentation and apoptotic cell death observed after TCR re-engagement are inhibited comparably in the presence of either 4-1BB or CD28 signaling.

Signals through 4-1BB are costimulatory to previously activated splenic T cells and inhibit activation-induced cell death

Previously, we and others showed that signals relayed through the murine T cell Ag 4-1BB enhance primary T cell responses, and that blocking the interaction of 4-1BB with its ligand results in decreased responses to polyclonal activators and to alloantigens. Because 4-1BB expression is induced following primary stimulation, we investigated the role of signaling through this molecule in the reactivation of proliferating T cells. To this end, preactivated, 4-1BB-expressing T cells were restimulated in the presence of plate-immobilized mAbs directed against 4-1BB or the prototypic costimulatory molecule CD28. In this work, we show that in the presence of either signal, T cells respond to TCR cross-linking with strong proliferative responses and cytokine production; moreover, our findings indicate that T cell proliferation partially correlates with surface 4-1BB expression. In addition, our results suggest that Ab-mediated costimulatory signals can act independently of potential accessory B7-CD28/CTLA-4 (cytotoxic T lymphocyte Ag-4) interactions. Importantly, the characteristic DNA fragmentation and apoptotic cell death observed after TCR re-engagement are inhibited comparably in the presence of either 4-1BB or CD28 signaling.

Potential role of 4-1BB in T cell activation. Comparison with the costimulatory molecule CD28

The expression of the murine T cell Ag 4-1BB, a member of the TNF-R family, is induced by T cell activation. Previously, we and others had shown that signaling through 4-1BB enhanced proliferative T cell responses. To investigate a potential role for the interaction of 4-1BB with its ligand (4-1BBL) in T cell activation, we studied the ability of a soluble chimera of 4-1BB (4-1BBFc) to interfere with proliferative responses and cytokine production in models of activation dependent in intercellular interactions. The potential blocking effect of 4-1BBFc was compared with that of the chimeric molecule CTLA-4Ig, a reagent known to interfere with the interaction of CD28 (and/or CTLA-4) with B7 costimulatory receptors. In this study, we report that 4-1BBFc partially blocked both the activation of unfractionated splenocytes triggered by soluble anti-CD3 (anti-CD3s), and the more physiologically relevant responses to alloantigen. In addition, we show that both chimeric molecules partially blocked proliferative responses and IL-2 secretion by highly purified resting T cells activated with anti-CD3s in the presence of fixed accessory cells that express B7 receptors and 4-1BBL. Furthermore, in this model system, the blocking capacity of 4-1BBFc and CTLA-4Ig appears to correlate with the relative expression of their respective cognate receptors (4-1BBL and B7) on the accessory cell. Simultaneous addition of both blocking reagents produced an additive effect in the model systems studied.

Potential role of 4-1BB in T cell activation. Comparison with the costimulatory molecule CD28

The expression of the murine T cell Ag 4-1BB, a member of the TNF-R family, is induced by T cell activation. Previously, we and others had shown that signaling through 4-1BB enhanced proliferative T cell responses. To investigate a potential role for the interaction of 4-1BB with its ligand (4-1BBL) in T cell activation, we studied the ability of a soluble chimera of 4-1BB (4-1BBFc) to interfere with proliferative responses and cytokine production in models of activation dependent in intercellular interactions. The potential blocking effect of 4-1BBFc was compared with that of the chimeric molecule CTLA-4Ig, a reagent known to interfere with the interaction of CD28 (and/or CTLA-4) with B7 costimulatory receptors. In this study, we report that 4-1BBFc partially blocked both the activation of unfractionated splenocytes triggered by soluble anti-CD3 (anti-CD3s), and the more physiologically relevant responses to alloantigen. In addition, we show that both chimeric molecules partially blocked proliferative responses and IL-2 secretion by highly purified resting T cells activated with anti-CD3s in the presence of fixed accessory cells that express B7 receptors and 4-1BBL. Furthermore, in this model system, the blocking capacity of 4-1BBFc and CTLA-4Ig appears to correlate with the relative expression of their respective cognate receptors (4-1BBL and B7) on the accessory cell. Simultaneous addition of both blocking reagents produced an additive effect in the model systems studied.

Interrelationships between immediate, intermediate, and delayed cutaneous reactions and their in vitro correlates

The mutual correlations between immediate, intermediate, and delayed cutaneous reactions, IgE, IgG, or combined IgG, A, and M antibody levels, and antigen- or mitogen-induced lymphocyte transformation were evaluated in a mixed group of allergic or non-allergic individuals. As might be expected, immediate and delayed reactions correlated significantly with IgE antibody levels and lymphocyte transformation, respectively. Intermediate time-course reactions did not correlate with IgG or IgG, A, and M antibody levels, but did so with immediate reactions, thus suggesting their "late phase" nature. Of particular interest was the finding of correlations that do not conform to the classical concept of the mechanisms involved in the generation of the different cutaneous reactions. Significant correlations were found between immediate or intermediate reactions and antigen-induced lymphocyte transformation, and between immediate and delayed reactions. These results are discussed in relation to recent suggestions that factors released from sensitized T cells can mediate early time-course reactions, and that such reactions may contribute to the manifestation of delayed-type hypersensitivity.

Humoral and cellular immune responses of atopic individuals in a tropical environment

In this study we compared immediate, intermediate and delayed skin test reactivity, total and specific serum IgE, IgG, A, M antibody and lymphocyte proliferative responses, between atopic and normal individuals in the tropical environment of Caracas, Venezuela (Lat. 10 degrees N). The allergenic extracts tested were prepared from house dust, mixed moulds and Aspergillus fumigatus. In lymphocyte stimulation the mitogen Concanavalin A was also employed, the cultures being supplemented with either autologous plasma, or a gamma globulin-depleted pool. The results revealed the association of immediate skin reactions with IgE antibody against house dust, and intermediate reactions with IgG, A, M antibody against moulds. No relation was, however, detected between delayed skin reactivity and in vitro lymphocyte transformation; skin reactions occurred at the highest frequency with moulds, while house dust provoked the strongest in vitro stimulation. Also, although the areas of positive delayed reactions were greatest in the atopic individuals, the lymphocyte proliferative responses were clearly highest in the normal subjects. The significance of the positivity of lymphocyte transformation tests in all of the study group, but lower reactivity in the atopics, is considered.