In adaptive antibody responses, B cells are induced to grow either in follicles where they form germinal centers or in extrafollicular foci as plasmablasts. Extrafollicular growth typically occurs in the medullary cords of lymph nodes and in foci in the red pulp of the spleen. It is not a feature of secondary lymphoid tissue associated with the internal epithelia of the body. All types of naïve and memory B cells can be recruited into extrafollicular responses. These responses are associated with immunoglobulin class switching but, at the most, only low-level hypermutation.

ObjectiveTo determine the rates of asymptomatic viral carriage and seroprevalence of SARS-CoV-2 antibodies in healthcare workers.DesignA cross-sectional study of asymptomatic healthcare workers undertaken on 24/25 April 2020.SettingUniversity Hospitals Birmingham NHS Foundation Trust (UHBFT), UK.Participants545 asymptomatic healthcare workers were recruited while at work. Participants were invited to participate via the UHBFT social media. Exclusion criteria included current symptoms consistent with COVID-19. No potential participants were excluded.InterventionParticipants volunteered a nasopharyngeal swab and a venous blood sample that were tested for SARS-CoV-2 RNA and anti-SARS-CoV-2 spike glycoprotein antibodies, respectively. Results were interpreted in the context of prior illnesses and the hospital departments in which participants worked.Main outcome measureProportion of participants demonstrating infection and positive SARS-CoV-2 serology.ResultsThe point prevalence of SARS-CoV-2 viral carriage was 2.4% (n=13/545). The overall seroprevalence of SARS-CoV-2 antibodies was 24.4% (n=126/516). Participants who reported prior symptomatic illness had higher seroprevalence (37.5% vs 17.1%, χ2=21.1034, p<0.0001) and quantitatively greater antibody responses than those who had remained asymptomatic. Seroprevalence was greatest among those working in housekeeping (34.5%), acute medicine (33.3%) and general internal medicine (30.3%), with lower rates observed in participants working in intensive care (14.8%). BAME (Black, Asian and minority ethnic) ethnicity was associated with a significantly increased risk of seropositivity (OR: 1.92, 95% CI 1.14 to 3.23, p=0.01). Working on the intensive care unit was associated with a significantly lower risk of seropositivity compared with working in other areas of the hospital (OR: 0.28, 95% CI 0.09 to 0.78, p=0.02).Conclusions and relevanceWe identify differences in the occupational risk of exposure to SARS-CoV-2 between hospital departments and confirm asymptomatic seroconversion occurs in healthcare workers. Further investigation of these observations is required to inform future infection control and occupational health practices.

Transposon-directed insertion site sequencing (TraDIS) is a high-throughput method coupling transposon mutagenesis with short-fragment DNA sequencing. It is commonly used to identify essential genes. Single gene deletion libraries are considered the gold standard for identifying essential genes. Currently, the TraDIS method has not been benchmarked against such libraries, and therefore, it remains unclear whether the two methodologies are comparable. To address this, a high-density transposon library was constructed in Escherichia coli K-12. Essential genes predicted from sequencing of this library were compared to existing essential gene databases. To decrease false-positive identification of essential genes, statistical data analysis included corrections for both gene length and genome length. Through this analysis, new essential genes and genes previously incorrectly designated essential were identified. We show that manual analysis of TraDIS data reveals novel features that would not have been detected by statistical analysis alone. Examples include short essential regions within genes, orientation-dependent effects, and fine-resolution identification of genome and protein features. Recognition of these insertion profiles in transposon mutagenesis data sets will assist genome annotation of less well characterized genomes and provides new insights into bacterial physiology and biochemistry.

We have shown that viruses are associated with 80 to 85% of asthma exacerbations in school-age children in the community. We hypothesize that viral infections are also associated with severe attacks of asthma precipitating hospital admissions. To investigate this, we conducted a time-trend analysis, comparing the seasonal patterns of respiratory infections and hospital admissions for asthma in adults and children. During a 1-yr study in the Southampton area of the United Kingdom, 108 school-age children monitored upper and lower respiratory symptoms and took peak expiratory flow rate (PEFR) recordings. From children reporting a symptomatic episode or a decrease in PEFR, samples were taken for detection of viruses and atypical bacteria. A total of 232 respiratory viruses and four atypical bacteria were detected. The half-monthly rates of upper respiratory infection were compared with the half-monthly rates for hospital admissions for asthma (International Classification of Diseases [ICD] code 493) for the same time period for the hospitals serving the areas from which the cohort of schoolchildren was drawn. The relationships of upper respiratory infections and hospital admissions for asthma with school attendance were studied. Strong correlations were found between the seasonal patterns of upper respiratory infections and hospital admissions for asthma (r = 0.72; p < 0.0001). This relationship was stronger for pediatric (r = 0.68; p < 0.0001) than for adult admissions (r = 0.53; p < 0.01). Upper respiratory infections and admissions for asthma were more frequent during periods of school attendance (87% of pediatric and 84% of total admissions), than during school holiday periods (p < 0.001). These relationships remained significant when allowance was made for linear trend and seasonal variation using multiple regression analysis (p < 0.01). Not surprisingly, school attendance, because it is a major factor in respiratory virus transmission, was found to be a major confounding variable in children. This study demonstrates that upper respiratory viral infections are strongly associated in time with hospital admissions for asthma in children and adults. Rhinoviruses were the major pathogen implicated, and the majority of viral infections and asthma admissions occurred during school attendance.