What do we mean by saying Ghana has performed more COVID-19 tests than Nigeria?

Background

I have heard on several platforms that Ghana is rated among some of the countries that are aggressively conducting COVID-19 tests among its populace. This was even a debate after one of the addresses given by the President of the Country.

Just by the television set on the evening of 24th June and on one of the media platforms, Ghana was mentioned to have performed more tests than Nigeria in the West of Africa. The figures were given as 270,000 tests conducted by Ghana compared to 120,108 tests conducted by Nigeria.

These figures synonymously represent the number of individuals that have been tested in the respective countries. But with the variance in approaches adopted by the two countries for testing, the number of tests performed may not be the same as the figures.

Ghana is known to have adopted the pooling of samples for a certain number of individuals to run as one test while Nigeria applies one test for each suspected COVID-19 case. as explained by the health authorities in Ghana in one of the media briefings, about 5 to 10 biological samples are pooled and tested as one sample. This means that if a test kit can run 50 individual patient samples, in pools of 5 samples, a total of 250 patient samples could be tested. The result for each pooled test represents all individual samples that were pooled together.  The individual samples will be tested singly if the pooled comes out positive, else all will be declared negative.

Making Assumptions of tests performed

Using the position of using pooling approach either in 5s or 10s together with 5% of tests performed for those pooled samples that needed to be handled singly after testing the pooled sample. These assumptions were done bearing in mind that about 1030 of the inbound travelers that were mandatorily quarantined. The assumption also considered the number of two consecutive tests that were performed to declare cases recovered as the earlier guidelines held.

Table 1: Scenarios considered for number of tests performed

Table 2: Total number of tests performed from each scenario

Discussions and Conclusions

Considering the three scenarios which I admit are not exhaustive, the highest number of tests Ghana could have conducted is 123,833. These are the tests performed on the 270,000 samples collected with the assumption that the samples that were subjected to pooling (237,810) did  50% each of “pools of 5 samples” and “pools of 10 samples” after taking out those done singly for the mandatory quarantined samples and the considered follow up tests to declare cases cleared of the virus.

The assumptions gave the least number of tests conducted to be 67,862 for the 270,000 samples collected from the beginning of testing in March 2020 to date. This was based on the assumptions made for Scenario 1 where all the pooling adopted were in “pools of 10 samples”. It must be noted that 5% of samples subjected to polling were allowed to account for un-pooling of positive pooled samples.

It is therefore not clear how it can be said that Ghana has done more COVID-19 tests than Nigeria (120,108 individual tests) with the strategy of pooling samples amidst single testing. It is only by scenario 3 that Ghana could have done more tests than Nigeria. Is it the case that figure 270,000 rather represent individual tests excluding pooling?  These are some of the reasons why I will support the call for the data to be made available to aid in some of these discussions.