A discussion on the minimum required number of tests in two common pooling test methods for SARS-CoV-2.

Pooling of samples in detecting the presence of virus is an effective and efficient strategy in screening carriers in a large population with low infection rate, leading to reduction in cost and time. There are a number of pooling test methods, some being simple and others being complicated. In such pooling tests, the most important parameter to decide is the pool or group size, which can be optimised mathematically. Two pooling methods are relatively simple. The minimum numbers required in these two tests for a population with known infection rate are discussed and compared. Results are useful for identifying asymptomatic carriers in a short time and in implementing health codes systems.

A discussion on implementing pooling detection tests of novel coronavirus (SARS-CoV-2) for a large population.

A pooled sample analysis strategy for novel coronavirus (severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2)) is proposed for a large population in this paper. The population to be tested is divided into divisions based on earlier observed detection rate of SARS-CoV-2 first. Samples collected are then grouped in appropriate pooled size. The number of tests per person in that population is expressed as a function of two variables: the observed detection rate and the pooled size or number of samples grouped. The minimum number of tests per person can be further shown to be a function of only one of these two variables, because these two parameters are found to be related at this minimum. A management scheme on grouping the samples is proposed in order to reduce the number of tests, to save time, which is of utmost importance in fighting an epidemic. The proposed testing scheme will be useful for supporting the government in making decisions to handle regular routine detection tests for identifying asymptomatic patients and implementing health code system in large population of millions of citizens. Another important point is to use smaller number of test kits, allowing more resources to speed up the mass screening tests, particularly in places not so rich.

A proposed two-stage quarantine containment scheme against spreading of novel coronavirus (SARS-CoV-2)

Novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is spreading rapidly all over the world with over 23 million infected near the end of August 2020. There are also asymptomatic patients (APs) who are difficult to identify, but they are infectious and believed to be one of the transmission sources. No specific medicine, no vaccine and even no reliable quick identification tests on SARS-CoV-2 are available yet. Workable safety management must be implemented to stop such global pandemic resulting from disease transmission, including those infected through APs. A two-stage containment scheme is proposed with quarantining people into units within blocks. The units inside a block is to be open after being closed for quarantine for an agreed period such as 14?days. The blocks would then be sealed for another period before opening. Argument of the proposal was supported by a simple mathematical approach with parameters deduced from observations on a cruise ship to estimate the infection constant. The proposed containment scheme is believed to be effective in controlling the spreading of SARS-CoV-2 and identifying APs by a more targeted screening test for the suspected group with a more acceptable environment at the second stage of containment.

Trajectories of large respiratory droplets in indoor environment: A simplified approach.

The recent pandemic of COVID-19 has brought about tremendous impact on every aspect of human activities all over the world. The main route of transmission is believed to be through coronavirus-bearing respiratory droplets. The respiratory droplets have a wide spectrum in droplet size, ranging from very small droplets (aerosol droplets) to large droplets of tens and even hundreds of µm in size. The large droplets are expected to move like projectiles under the action of gravity force, buoyancy force and air resistance. Droplet motion is complicated by droplet evaporation, which reduces droplet size in its trajectory and affects the force acting on it. The present work attempts to determine the trajectories of the large droplets by using a simplified single-droplet approach. It aims at providing a clear physical picture to elucidate the mechanics involved in single droplet motion and the various factors affecting the range. Assuming an indoor environment with an air temperature of 18 °C and relative humidity of 50%, the horizontal range L x of large respiratory droplets (diameter 120 µm-200 µm) in common respiratory activities are as follows: Speaking, L x ≈ 0.16 m-0.68 m, coughing, L x ≈ 0.58 m-1.09 m, and sneezing, L x ≈ 1.34 m-2.76 m. For the smaller droplets (diameter < 100 µm), the droplets are reduced to aerosol droplets (≤5 µm) due to evaporation, and will remain suspended in the air instead of falling onto the ground like a projectile.