Contact tracing is the process of identifying the person who have made contact with an infected individual testing positive for disease. The main objective of contact tracing is to trace contact made by infected individual and test them for infection and treating infected person.
Followings are the reason behind contact tracing:-
- To reduce and interrupt further transmission
- To find number of contacts made by infected person
- To know about distribution, patterns of disease in particular population
- To formulate rules and technique required by government to stop transmission
- To alert person to go for checkup who have contacted infected person
In past contact tracing was used for tuberculosis, measles, HIV, bacterial infection and novel disease SARS-CoV and SARS-CoV-2.
Contact tracing is the first task to be performed by country, community or society to interrupt further transmission. Sometimes contact tracing can also help to learn about disease its spreading medium, disease characteristics including its symptom. When contacts are identified public health officer, health worker can contact them to offer counseling, screening, testing and treatment. Contact tracing can be used to determine if outbreaks disease, infections is linked with known disease from past.
Apple and Google Collaboration to fight Covid-19
Big two tech giants Apple and Google engineering team has collaborated to create decentralized contact tracing tool to determine whether individual is exposed to covid-19 infected person. This tool will help public health agencies to identify and follow up with people who have come in contact with covid-19 infected person.
In first phase Google and Apple are going to release API so that public health agencies can integrate contact tracing to their app. In second phase they are going to make system that will work on cross platform Android and IOS.
The system uses Bluetooth Low Energy of mobile device to transmit an anonymous ID over time period. When two people came in contact then both devices will transmit their unique id to each other and save it to server (it can be local or remote). Server store and check rotating ID for 14 days for match. Match is made when threshold of time of contact and distance between devices are out of threshold value. When system found match with infected person then it notifies another person to test and self-quarantine.
How will app works
- When two people comes near for certain period of time then their device will exchange anonymous identifier (which changes every 15 minutes).
- When one person is diagnosed with Covid-19 and enters into system with public health authority app that has integrated API.
- Diagnosed user allows his anonymous identifier for last 14 days to be transmitted to the system.
- Person who came into to contact with infected person will download the broadcast keys of infected person. When match is made it will alerts them and send more information how to proceed from there.
Technical Problems with contact tracing app
Contact tracing app uses Bluetooth Low Energy (BLE) whose working module was introduced in 1999A.D. So we are using 21 years old mechanism which operates from 2.402 GHz to 2.490 GHz. Contact tracing has simple mechanism. Bluetooth continuously search for another Bluetooth device near them. When two devices have near contact for certain period of time (minimum 10 minutes let say), then devices will stores receive anonymous ID. When someone gets infected with covid-19 then app will alert another person who was contact with patient. It will inform further guidelines to follow.
Getting correct information is technically difficult task for 21 years technology. WHO has declared maintaining six feet or two meter social distancing from other people but we still don’t know correct measurement of how long will it take and how much distance will put us at risk.
Contact tracing app uses Bluetooth as it is low power signal and it is available in most of phones, it is highly resistant to blockage and can be used to preserve privacy. Bluetooth can measure strength of a signal from another phone. It is called RSSI (Receiver Signal Strength Indicator). We have amount of power is proportional to distance and we can find the distance between two devices.
When will it go wrong?
Bluetooth are low power signal and highly resistant to blockage. Due to this feature contact tracing technology can go wrong as app will yield many false positive. In this post we are going to state two cases.
First case: –
When Person A opens app then his/her device Bluetooth will scan surrounding devices. It can store ID of person B living next door or next floor as smaller partition can’t block Bluetooth. Also Bluetooth operates from 2.402 GHz to 2.480 GHz so difference in operating frequency can effect app.
Second Case: –
When two person are in contact (scenario of having person contact with back touch) then the signals are transmitted through our bodies. App might calculate wrong distance covered by signal to reach another device. These can confuse app to function properly
Bluetooth contract tracing needs lots of quality data because one single mismatch can make a lot of false alert which can terrify public. This contact tracing app has raised privacy concerns. Singapore’s app allows data to be collected and decrypted by a central authority, something which gives the government a lot of data about people’s movements. Any centralized data collection invites privacy risks. So designing decentralized app for contact tracing can mitigate risk of privacy loss. There are other sensors such as GPS, ambient light, Gyroscope in mobile device which can increase the effectiveness of contract tracing.