391 research outputs found

    Viral load and antibody boosting following herpes zoster diagnosis

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    BACKGROUND: Acute varicella zoster virus (VZV) replication in shingles is accompanied by VZV antibody boosting. It is unclear whether persisting virus shedding affects antibody levels. OBJECTIVES: To investigate the relationship between VZV viral load and antibody titres in shingles patients during six months following diagnosis and assess whether VZV antibody titre could discriminate patients with recent shingles from healthy population controls. STUDY DESIGN: A prospective study of 63 patients with active zoster. Blood samples were collected at baseline, one, three and six months to measure VZV DNA and IgG antibody titre. We compared VZV antibody titres of zoster patients and 441 controls. RESULTS: In acute zoster, viral load was highest at baseline and declined gradually over the following six months. Mean antibody titres rose fourfold, peaking at one month and remaining above baseline levels throughout the study. Antibody levels at one, three and six months after zoster were moderately correlated with baseline but not subsequent viral load. Regarding use of antibody titres to identify recent shingles, to achieve 80% sensitivity, specificity would be 23.4%, 67.7%, 64.8% and 52.6%, at baseline, visit 2, 3 and 4 respectively, whilst to achieve 80% specificity, sensitivity would be 28.3%, 66.1%, 52.6%, 38.6%, at baseline, visit 2, 3 and 4 respectively. CONCLUSIONS: Clinical VZV reactivation boosted VZV antibody levels and the level of boosting was dependent upon baseline viral replication. While antibody titres could discriminate patients with shingles 1-6 months earlier from blood donor controls, there was a large trade-off between sensitivity and specificity

    Ethnic differences in the incidence of clinically diagnosed influenza: an England population-based cohort study 2008-2018 [version 2; peer review: 2 approved]

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    Background: People of non-White ethnicity have a higher risk of severe outcomes following influenza infection. It is unclear whether this is driven by an increased risk of infection or complications. We therefore aimed to investigate the incidence of clinically diagnosed influenza/influenza-like illness (ILI) by ethnicity in England from 2008-2018. Methods: We used linked primary and secondary healthcare data (from the Clinical Practice Research Datalink [CPRD] GOLD and Aurum databases and Hospital Episodes Statistics Admitted Patient Care [HES APC]). We included patients with recorded ethnicity who were aged 40-64 years and did not have a chronic health condition that would render them eligible for influenza vaccination. ILI infection was identified from diagnostic codes in CPRD and HES APC. We calculated crude annual infection incidence rates by ethnic group. Multivariable Poisson regression models with random effects were used to estimate any ethnic disparities in infection risk. Our main analysis adjusted for age, sex, and influenza year. Results: A total of 3,735,308 adults aged 40-64 years were included in the study; 87.6% White, 5.2% South Asian, 4.2% Black, 1.9% Other, and 1.1% Mixed. We identified 102,316 ILI episodes recorded among 94,623 patients. The rate of ILI was highest in the South Asian (9.6 per 1,000 person-years), Black (8.4 per 1,000 person-years) and Mixed (6.9 per 1,000 person-years) ethnic groups. The ILI rate in the White ethnic group was 5.7 per 1,000 person-years. After adjustment for age sex and influenza year, higher incidence rate ratios (IRR) for ILI were seen for South Asian (1.70, 95% CI 1.66-1.75), Black (1.48, 1.44-1.53) and Mixed (1.22, 1.15-1.30) groups compared to White ethnicity. Conclusions: Our results suggest that influenza infection risk differs between White and non-White groups who are not eligible for routine influenza vaccination

    Derivation of the aerodynamic roughness parameters for a Sahelian savannah site using the eddy correlation technique

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    Vertical exchange of heat, moisture and momentum above the earth's surface depends strongly on the turbulence generated by surface roughness. This roughness is best specified through the roughness length and the zero plane displacement. The ratio of windspeed to friction velocity was measured at four heights using the eddy correlation technique at a fallow savannah site in the Sahel. The change in this ratio with height was used to derive the zero plane displacement and the roughness length of the surface, together with an estimate of the error in each parameter. These were estimated as 0.93 ± 0.35 m and 0.17 ± 0.01 m, respectively. The method appears to be a more robust alternative to wind profile derivation

    Preliminary measurements of net radiation and evaporation over bare soil and fallow bushland in the Sahel

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    Net radiation and evaporation are compared over two contrasting land surfaces, fallow bushland and bare soil, in Niger, West Africa. Data are presented for 6 days, before and after a large rainstorm (39 mm), which illustrate how evaporation from the bush vegetation changed little in comparison with the larger change in evaporation observed over the bare soil. Net radiation over the bush vegetation was 20 per cent greater than that over the dry bare soil, but only 12 per cent greater than that over wet bare soil. These differences are consistent with the expected difference in albedo and surface temperature of the two surface

    Measurements of albedo variation over natural vegetation in the sahel

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    This paper reports ground-based measurements of albedo at two different sites in south-western Niger: agricultural fallow at the ICRISAT Sahelian Center (ISC), Sadoré, and a type of open natural forest (tiger-bush), 6 km south-west of ISC. The vegetative cover at each site consisted of two clearly defined components, for which separate measurements were made. The four different component surfaces spanned the entire range of plant cover density normally occurring in the southern Sahel, ranging from zero (bare soil) to a dense, closed canopy of woody shrubs. Continuous automated observations of albedo were made over a period of 15 months, from July 1989 to September 1990, including both wet and dry seasons. The data are analysed on hourly, monthly, and annual time-scales in order to demonstrate how albedo varies in response to the density of plant cover, soil-surface moisture content, solar zenith angle, and the proportion of diffuse light in the incoming solar radiation. Large annual variation in monthly mean albedo was observed at both sites (increases from the wet to dry season of 0.065 and 0.057 for the fallow and tiger-bush, respectively). At the fallow site the annual variation in albedo resulted mainly from the wet to dry season cycle of leaf growth and loss. At the tiger-bush site the primary cause of annual variation in albedo was the frequent wetting of the extensive bare soil component that occurred during the rainy season. The significance of these results for global climate modelling is assessed briefly

    Measurements of evaporation from fallow Sahelian savannah at the start of the dry season

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    Micrometeorological measurements of evaporation were made for the first six weeks of the dry season at a fallow savannah site in the Sahel. The evaporation fell from typically 4.5 mm per day at the start of the dry season to 1.5 mm per day six weeks later. The surface conductance was modelled in terms of empirical functions of time of day, and the number of days since the final rain of the season. It was found that there was little variation in surface conductance within each day, with no significant correlation with solar radiation and only a weak correlation with humidity deficit. Daily values of the surface conductance necessary to estimate the actual evaporation, from the data provided by a standard climate station, were also derived

    Amazonian evaporation.

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    Medições de evaporação da cobertura vegetal seca e perdas por intercepção obtidas durante um estudo de dois anos de evaporação na floresta tropical no centro da Amazônia são utilizados para calibrar um modelo micrometeorológico de evaporação
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