Laboratory Modeling of SARS-CoV-2 Exposure Reduction Through Physically Distanced Seating in Aircraft Cabins Using Bacteriophage Aerosol - November 2020.

Aircraft can hold large numbers of persons in close proximity for long periods, which can increase the risk for transmission of infectious disease.* Current CDC guidelines recommend against travel for persons who have not been vaccinated against COVID-19, and a January 2021 CDC order requires masking for all persons while on airplanes.†,§ Research suggests that seating proximity on aircraft is associated with increased risk for infection with SARS-CoV-2, the virus that causes COVID-19 (1,2). However, studies quantifying the benefit of specific distancing strategies to prevent transmission, such as keeping aircraft cabin middle seats vacant, are limited. Using bacteriophage MS2 virus as a surrogate for airborne SARS-CoV-2, CDC and Kansas State University (KSU) modeled the relationship between SARS-CoV-2 exposure and aircraft seating proximity, including full occupancy and vacant middle seat occupancy scenarios. Compared with exposures in full occupancy scenarios, relative exposure in vacant middle seat scenarios was reduced by 23% to 57% depending upon the modeling approach. A 23% exposure reduction was observed for a single passenger who was in the same row and two seats away from the SARS-COV-2 source, rather than in an adjacent middle seat. When quantifying exposure reduction to a full 120-passenger cabin rather than to a single person, exposure reductions ranging from 35.0% to 39.4% were predicted. A 57% exposure reduction was observed under the vacant middle seat condition in a scenario involving a three-row section that contained a mix of SARS-CoV-2 sources and other passengers. Based on this laboratory model, a vacant middle seat reduces risk for exposure to SARS-CoV-2 from nearby passengers. These data suggest that increasing physical distance between passengers and lowering passenger density could help reduce potential COVID-19 exposures during air travel. Physical distancing of airplane passengers, including through policies such as middle seat vacancy, could provide additional reductions in SARS-CoV-2 exposure risk.

Airborne exposure patterns from a passenger source in aircraft cabins.

Airflow is a critical factor that influences air quality, airborne contaminant distribution, and disease transmission in commercial airliner cabins. The general aircraft-cabin air-contaminant transport effect model seeks to build exposure-spatial relationships between contaminant sources and receptors, quantify the uncertainty, and provide a platform for incorporation of data from a variety of studies. Knowledge of infection risk to flight crews and passengers is needed to form a coherent response to an unfolding epidemic, and infection risk may have an airborne pathogen exposure component. The general aircraf-tcabin air-contaminant transport effect model was applied to datasets from the University of Illinois and Kansas State University and also to case study information from a flight with probable severe acute respiratory syndrome transmission. Data were fit to regression curves, where the dependent variable was contaminant concentration (normalized for source strength and ventilation rate), and the independent variable was distance between source and measurement locations. The data-driven model showed exposure to viable small droplets and post-evaporation nuclei at a source distance of several rows in a mock-up of a twin-aisle airliner with seven seats per row. Similar behavior was observed in tracer gas, particle experiments, and flight infection data for severe acute respiratory syndrome. The study supports the airborne pathway as part of the matrix of possible disease transmission modes in aircraft cabins.

Drainage of pancreatic pseudocysts. The importance of cyst wall biopsy in the recent era.

OBJECTIVE: While open internal drainage has been the standard treatment for pancreatic pseudocysts, less invasive techniques which pay little attention to cyst wall biopsy, are becoming popular. The aim of this study is to report on our experience in draining pancreatic pseudocysts and probe the necessity or otherwise of obtaining a wall biopsy at drainage. METHODS: Operation theatre registry, operation log books and medical records at Aseer Central Hospital, Abha, Kingdom of Saudi Arabia, were reviewed to retrieve the clinical details of patients with pancreatic pseudocyst who required a drainage procedure in a 13 years period from August 1989 to November 2002. RESULTS: Sixteen patients were identified. Cyst wall biopsy was obtained in 10 cases, in 8 of them the diagnosis was confirmed, while a true cyst was found in the remaining 2 excluding them from further analysis. In the remaining 14 cases (8 males, 6 females, mean age 38 years, range 4-60), pain was the main presenting feature. Open internal drainage was offered to 12 cases while one patient received external drainage under ultrasound guidance and the other received open external drainage. The type of operation was cystogastrostomy in 9 patients and cystojejunostomy in 3 patients. The recurrence rate after internal drainage was 16.7%, while after external drainage was 100%. There was no mortality in this series. A procedure-related complication occurred in 3 (21.4%) patients. CONCLUSION: The mortality, morbidity and recurrence rates in this series are compared favorably with other reports. The final diagnosis of a presumed pancreatic pseudocyst should rest on the histopathologic examination of the cyst wall.

Comparison of emission models with computational fluid dynamic simulation and a proposed improved model.

Understanding source behavior is important in controlling exposure to airborne contaminants. Industrial hygienists are often asked to infer emission information from room concentration data. This is not easily done, but models that make simplifying assumptions regarding contaminant transport are frequently used. The errors resulting from these assumptions are not yet well understood. This study compares emission estimates from the single-zone completely mixed (CM-1), two-zone completely mixed (CM-2), and uniform diffusivity (UD) models with the emissions set as boundary conditions in computational fluid dynamic (CFD) simulations of a workplace. The room airflow and concentration fields were computed using Fluent 4. These numerical experiments were factorial combinations of three source locations, five receptor locations, three dilution airflow rates, and two generation rate profiles, constant and time-varying. The aim was to compute plausible concentration fields, not to simulate exactly the processes in a real workroom. Thus, error is defined here as the difference between model and CFD predictions. For the steady-state case the UD model had the lowest error. When the source near-field contained the breathing zone receptor, the CM-2 model was applied. Then, in decreasing agreement with CFD were UD, CM-2, and CM-1. Averaging over all source and receptor locations (CM-2 applied for only one), in decreasing order of agreement with CFD were UD, CM-1, and CM-2. Source and receptor location had large effects on emission estimates using the CM-1 model and some effect using the UD model. A location-specific mixing factor (location factor) derived from steady-state concentration gradients was used to build a more accurate time-dependent emission model, CM-L. Total mass emitted from a time-varying source was modeled most accurately by CM-L, followed by CM-1 and CM-2.

Choledochocele: the disputed origin.

Choledochocele is classified as a type III choledochal cyst according to Alonso-Lej classification. Although it is anatomically related to the common bile duct, it does not share the strong premalignant potential of the more common types of choledochal cysts. In addition, duodenal mucosa has been found lining many of these cysts. These findings pose certain disputes about their possible origin, necessitating revision of the current inclusion of choledochocele with choledochal cysts.