COVID-19 Scan for Feb 10, 2021

COVID-19 far deadlier than flu
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Air conditioning and COVID spread
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Exhaling COVID-19 aerosols

COVID associated with more hospitalizations, ICU care, mortality than flu

Hospitalized adults with COVID-19 are 3.5 times more likely to die than adults with the flu, reports a study today in CMAJ. The study also found that those with COVID were 1.5 times more likely to be admitted to the intensive care unit (ICU) and have 1.5 times longer hospital stays.

The researchers collected data from seven hospitals in Toronto and Mississauga in Canada and found that, from November 2019 through June 2020, 763 patients were admitted 783 times with the flu and 972 patients were admitted 1,027 times with COVID-19—the latter making up 23.5% of all hospitalizations during the study's duration.

Unadjusted in-hospital mortality for COVID and flu patients was 19.9% and 6.1%, respectively, and COVID patients similarly had higher rates of ICU admittance (26.4% vs 18.0%) and longer hospital stays (8.7 vs 4.8 median days). The adjusted relative risk for COVID patients was 3.46 for death, 1.50 for ICU use, and 1.45 for length of hospital stay.

Thirty-day readmission was not significantly different between COVID and flu patients at 9.3% and 9.6%, respectively.

More than 1 in 5 COVID hospital admissions (21.2%) were for adults younger than 50; this group made up 24.0% of COVID ICU admissions and almost 1 in 10 COVID readmissions, according to a CMAJ press release. In general, those with COVID were more likely to have no comorbidities (54.1% vs 38.8%) and reside in long-term care (11.7% vs 4.5%) than those with the flu. Lower-income residents made up disproportionately high percentages of hospital patients for both illnesses (34.2% vs 31.7%).

"These differences may be magnified by low levels of immunity to the novel coronavirus compared with seasonal influenza, which results from past infections and vaccination," said first author Amol Verma, MD, in the release. "Hopefully, the severity of COVID-19 will decrease over time as people are vaccinated against the virus and more effective treatments are identified. There is, unfortunately, also the possibility that variants of the virus could be even more severe."
Feb 10 CMAJ study
Feb 10 CMAJ press release

 

Fluid dynamics highlight role of air conditioning in indoor COVID spread

Computational fluid dynamics can help assess transmission risk of airborne COVID-19 particles, according to a study published yesterday in Physics of Fluids. The researchers, from the University of Minnesota, found that their modeling of a January 2020 COVID outbreak in a restaurant in Guangzhou, China, supports the idea that air conditioning contributed to disease transmission.

After mapping out the general layout of the restaurant, its ventilation systems, and its occupants, the researchers discerned that the cyclical flow of air from the four heating, ventilation, and air conditioning (HVAC) units along the wall was disrupted by factors including hemispherical hot regions above each table due to food heat, the restaurant's occupants, and the presence of a fifth, floor-level HVAC unit on the adjacent wall.

Recirculation zones were found throughout the restaurant, such as one above one table created by the interaction between the walls and ceiling, the table, and the thermal differences between empty space and occupied space. Additionally, they found that particles from the HVAC units were projected laterally from the unit before sinking down to be carried by currents underneath the tables before being sucked up vertically into the units again.

"Our work highlights the need for more preventive measures, such as shielding more properly underneath the table and improving the filtration efficiency of air conditioners," senior author Jiarong Hong, PhD, said in an American Institute of Physics (AIP) press release.

Based on their results, the researchers write, "Aerosols can contribute as high as 30% to the total infection risk in some ventilation and thermal settings."
Feb 9 Phys Fluids study
Feb 9 AIP
press release

 

COVID-19 aerosol load associated with infection, age, obesity

The number of COVID-19 aerosol droplets a person exhales is positively associated with infection, age, and obesity, finds an observational study published yesterday in the Proceedings of the National Academy of Sciences.

The researchers looked at 194 healthy people to measure general aerosol rates as well as 8 COVID-infected nonhuman primates (NHPs) to look at how infection progression affected aerosol quantity and size. Human participants were asked to spend up to 30 minutes per session breathing into a mouthpiece connected to a particle detector.

The NHPs (rhesus macaques and African green monkeys) were infected with SARS-CoV-2, the virus that causes COVID-19, and the researchers collected biosamples from them and had them breathe into a modified pediatric face mask connected to a particle counter.

Among the human group, which consisted of 74 food workers in North Carolina and 120 students, staff, and faculty at a community college in Michigan, aerosol creation appeared to follow the 20:80 superspreader rule, with 35 exhaling 80% of the aerosols. The researchers write that aging, diet, and lung quality are all accepted factors of mucus composition. They found that the 73 people with the lowest BMI-years (age multiplied by BMI, or body mass index) exhaled less aerosol compared with the 73 with the highest BMI-years.  

The NHP portion of the study indicated that aerosol production followed SARS-CoV-2 viral replication patterns by increasing around day 3 post-infection, peaking at about day 7, declining rapidly by day 14, and undetectable by day 27. Aerosol sizes were at their smallest during peak infection.

To assess another respiratory infection, the researchers gave four rhesus macaques tuberculosis and found similar results.

The researchers conclude, "These findings suggest that quantitative assessment and control of exhaled aerosol may be critical to slowing the airborne spread of COVID-19 in the absence of an effective and widely disseminated vaccine."
Feb 10 Proc Natl Acad Sci study

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