Covid-19 crisis Rationale of contact tracing
Contact tracing is effective when the number of infected persons is low, say less than say 500. It is possible to trace all the people who have been in contact with the infected person and ask them to go for testing or isolation.

It is difficult to carry out contact tracing when there is a large number of infected people in the community. Any new case could be infected by any of the previously infected person. It will be difficult to trace the source of contact. It might even give misleading results - for example X is thought to be infected by Y when he was actually infected by Z.

During the past few weeks, we read about several tens of new cases which could not be traced.  The cumulative total of untraced cases is not reported, but is estimated to number a few hundreds.

I think that it is time to abandon the contact tracing efforts, as it takes a lot of resources and do not provide any useful outcome. 

Before taking this decision, it is better to make an estimate of the proportion of infected people in the community. There are three ways to do it.

a) Select from the existing tests that have already been carried out, the tests that can be considered as random, i.e. exclude those conducted on people with fever or living in the worker dormitories. The proportion found positive could be indicative of the general population.

b) Carry out the covid test on all essential workers - health workers, delivery workers and transport workers. As they do not have any symptoms, they can be considered to represent the general population. The proportion tested positive can be used as an estimate of the infection rate in the population.

c) Carry out the covid test from a representative sample of the population selected at random. This sample reflects the actual proportion by age group, ethnic group and social economic background. This method is used for statistical polls.

I prefer that (a) be carried out now. If the data is not reliable, we can conduct (b). Actually, (b) is useful to protect the workers and the community, and should be done anyway. However, we should also pay attention for its statistical purpose.

We only need to consider (c) at a later date, if it is really necessary.

If the tests indicate that 1% of the population is already infected, i.e. they have the virus and have not shown symptoms, it would mean that 60,000 people are already infected. It will be useless to continue with contact tracing.

My guess is that the tests will show that more than 5% of the population is  already infected. I based this guess on several reports of similar data from other countries.

It is important to carry out the tests to decide on the strategy of containment. I hope that the ministerial task force will take up this suggestion.

Tan Kin Lian

Vote - agree or not?

 

Add Comment

---