How the Seventh-Day Amplification Factor can gauge the Existence of Corona Silent Carriers
By: Worsak Kanok-Nukulchai
Tags: Covid 19, Data Analysis, Coronavirus, Data Science, Data

How the Seventh-Day Amplification Factor can gauge the Existence of Corona Silent Carriers

If the value of A7=1.0, then the total confirmed cases of infection on Day 7 are equal to that of Day 0. This means that there have been no new infections.

A key challenge is confronting the Corona outbreak has been a relative inability to estimate the number of silent carriers. Silent carriers can prove to be more critical than the numbers of known infections, since infected individuals can be quarantined and subject to contact tracing; while silent carriers cannot be identified.

We can, however, qualitatively gauge the existence of silent carriers by using a mathematical expression — the Seventh-Day Amplification Factor (A7). If we compute the ratio of total cases of confirmed infection today (Day 7) over that of seven days ago (Day 0), we arrive at the ratio called the “7th-day Amplification Factor,” or A7. A7 is always higher or equal to 1.0. The portion over 1.0 refers to the increase, in fraction of Day 0 figure, due to the new cases accumulated over the last 7 days

This is a simple mathematical ratio of cumulative COVID-19 infections between two points seven day apart. A 3-day rolling average is used at both ends to eliminate daily fluctuations.

The ratio is based on some assumptions:

Assumptions

Patients who test positive today have caught the virus at least seven days ago (assuming five days of incubation and two days of testing). These patients (whom we can call Day-7 patients) were infected by Day-0 Silent Carriers, and not by Day-0 patients (since they were already quarantined). The silent patients represent 80 percent of all infected cases, or about four times the number of Day-0 patients. Many “silent patients” may have already recovered, and thus only active ones can transmit the virus.

Usefulness of A-7 Simulation

This ratio can be used in three ways

To monitor current trends To analyse the effectiveness of the state intervention To forecast the end of the outbreak.

Why is A-7 Important?

It is shown to be qualitatively related to the asymptomatic infected persons mingling in the society, known as “silent patients.” In the absence of mass testing in most countries, it is critical to prefigure the existence of these silent patients. This monitoring is needed by the governments to implement interventionist measures, as well as by public health officials to estimate their ability to cater to a sudden surge in the number of patients. It also helps in informing the public about the severity of the crisis and the necessity of citizen participation in implementing measures like social distancing and adhering to precautionary measures.

The Perfect Ratio of “1.0” When the ratio A-7 is more than 1.0, then the portion over 1.0 is due to the new cases of infection that have been added since Day-0. If the value of A7=1.0, then the total confirmed cases of infection on Day 7 are equal to that of Day 0. This means that there have been no new infections, and therefore no silent carriers who have transmitted the virus from Day 0 or any day in the week earlier.

Examples