A Look Behind LCT

A CoronaVirus Early Warning System (CVEW)

LCT is a collaborative effort between Soteria Institute (Oregon, USA) and Enduring Net!

Risk Assessment Strategy

We start with four basic conditions a carrier can have (in order of weight of evidence of exposure):


  • Person tested positive for COVID-19 (weight=10)
  • Person presents symptoms of COVID-19 (weight=6)


  • Person was near a carrier (weight=3)
  • Person was warned by LCT of a possible exposure (weight=2)

Each condition listed above has a somewhat arbitrary weight of evidence[1]. The weights were chosen with the following goals in mind:

  • Weights decrease from 10 to 2
  • The odds of a correct assessment of risk is reasonable (viz., from 10:1 down to (about) 3:2)
  • We can sum one to four conditions to produce a single unique number that can point to a written description of the specified circumstances

The program interprets any give score (the sum of one to four conditions) accordingly (note: if vaccinated, we add 1 to the score so we can make further inferences based on evidence):

Case   Warning Message
2If you received an LCT exposure alert, you SHOULD get tested immediately. If you are positive, hit the Warn button and take care of yourself.
3If you were near someone who tested positive AND you received an LCT Exposure Alert, you really MUST get tested, and act accordingly.
4Since you are vaccinated, you may not need to warn others that you have been close to a carrier, especially if you wear a mask.
5Being near someone who tested positive for COVID is weak evidence that you too are carrying the virus now.
7Showing COVID symptoms is strong evidence of infection (especially since your recent flu shot, as the symptoms could not be due to flu).
Showing COVID symptoms is strong evidence of infection unless the symptoms might be due to flu).
8Since you show symptoms AND you see an alert, you may be in a vulnerable community. You can send an alert now, then get tested; or you can wait for your test results to ensure your symptoms are from COVID (and not the flu) before warning others of exposure.
9You are vaccinated, but it looks like you live in an active COVID zone. Get tested to check if you are a breakthrough case and warn others if tested positive.
10Testing positive is the most reliable signal of COVID exposure.
11You tested positive after your vaccination. Because you have a breakthrough infection, you SHOULD hit the Warn button as a symptomatic carrier. Please always wear a mask.
12If you tested positive AND received an LCT Exposure Alert, you may be vulnerable to high community spread. Thank you for warning others of this likelihood.
13If you tested positive AND you think you got the virus from somebody else, you have evidence of community spread. Thank you for warning others of this likelihood.
14You tested positive AND you think you got the virus from somebody else. You MUST keep wearing your mask, and you SHOULD alert others of exposure.
15You have almost checked all the boxes. Since you are not showing symptoms, yourself, you may be an asymptomatic carrier especially if you are vaccinated.
16You are more likely to have COVID if you test positive AND show symptoms. Without a covid test, if you had a flu shot recently, your symptoms are less likely to be from the flu and more likely from COVID. Without a recent flu shot, your symptoms might not be due to COVID.
17Despite wearing a mask (you are tested positive), you are an at-risk breakthrough case. You MUST warn others of exposure. Then take care of yourself.
19Not only that you are highly likely to have infected others (some of whom might have infected you), there is evidence of high community spread (especially if you also receive exposure alerts from LCT).
21Despite wearing a mask, you are in the middle of the pandemic of the unvaccinated. It's not too late. You MUST warn others of exposure and take care of yourself.
22Despite wearing a mask, you are an at-risk breakthrough case. Evidence suggests you are in an area with a high rate of community spread. You MUST warn others of exposure and take care of yourself.

Managing Time of Events

(i) Past Events

LCT is basically a COVID-aware Calendar. Unlike conventional COVID-19  apps based on GPS/Bluetooth, LCT users can make note of their locations at any time. For instance, after a busy day, the user can sit down with their phone or at their computer to document the place and times they visited that day (or any day within the last ten days).

(ii) Current Events

For convenience, LCT assumes real-time use. When you select a place on the LCT map, the Calendar component adds an event with the current time as default. Users can change the day or the time slot at will. Once the day/time is correct, the user can log the event to the exposure graph. Any later changes to a logged event update the graph, as well.

(iii) Future Events (appointments)

We define an appointment as any event to occur in the future. By default, then, any event entered on the LCT Calendar in the future constitutes an appointment. The next version of LCT will take the second step to make appointments useful: to bind two or more parties to the same point in spacetime. This way, service providers (who, due to COVID-19  mandates can only serve customers with appointments) can further protect themselves from unrecognized exposure if any past customer sends an LCT Warning.

Managing Space

  • Public spaces with publicly recognizable names
  • Open spaces without public names

Managing People

  • Individual Travel Logs
  • Bubbles


  • LCT/CVEW works best with congregations of people. For example, church congregations and large offices are prime candidates. Other good candidates are classrooms or even small university seminars and lectures.
  • LCT/CVEW reduces the time between exposure and notification of risk to the smallest possible interval. This is done by tracing interactions before testing or conventional human contact tracing. In other words, LCT can trace contacts in seconds where human contact tracers can take days (if they even manage to stay ahead of rate of incoming subjects).
  • The goal of LCT/CVEW is to get potentially exposed individuals tested as soon as possible. If they test positive, they warn LCT/CVEW. If they are negative, they continue about their business.
  • As users are more dispersed, the chances of interacting with each other diminish.
  • At the very least, users have a ready contact list for human contact tracers to use.

Go to Introduction, User Guide, or Data Policy.   If you have any questions or feedback, please Email Us.

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