Microbiologist explains Corona test variances

Monday, July 6th, 2020 00:00 |
Prof Matilu Mwau, the head of Kenya Medical Research Institute testing and research centre. Photo/FILE

A top researcher on viruses has come out to explain the variances of results of Covid-19 tests released by the Lancet Laboratories Kenya.

Prof Matilu Mwau, the head of Kenya Medical Research Institute (Kemri) testing and research centre and a microbiologist, says both results released by Lancet and other testing medical facilities were correct depending on the specific gene sequences one is looking for.

In all circumstances, scientists use Polymerise Chain Reaction (PCR) to test for Covid-19.

“At the moment, the majority of the current Covid-19 tests that all the reports are coming from using PCR,” says Mwau, who is also a microbiology lecturer at the Jomo Kenyatta University of Agriculture and Technology (Jkuat) and a visiting professor of molecular medicine at Nagasaki University of Medicine in Japan.

“They detect the genetic information of the virus, the RNA. That’s only possible if the virus is there and someone is actively infected.”

According to Mwau, an expert in molecular biology and infectious diseases, there are three types of genes that researchers go for when testing for Covid-19 — E-gene, RdRp gene and N-gene.

The E-gene, which most laboratories use, is used to determine the existence of all types of coronaviruses, and thus would give positive results for any common virus such as flu, cold or simple cough.

“In medical parlance, we call this testing indeterminate because it cannot be used as a conclusion that an individual has Covid-19 and that is why most doctors would demand for a second test to make a final decision,” he says.

The RdRp and E-gene tests are more specific in looking for the Severe Acute Respiratory Syndrome-2  (SARS-Cov-2), the strain of coronavirus that causes coronavirus disease 2019 (Covid-19).


Due to the heavy financial weight required to purchase equipment for testing of the three genes, most laboratories such as Kemri are only able to invest in the E-gene machines.

According to Mwau, there have been cases where an individual could test positive at a facility using the E-gene machines and then test negative from a facility using both RdRp and N-genes.

“This does not mean that one of the results is incorrect. The only difference is the specific gene sequence the scientist may have been looking for and the machine used for the test,” Mwau told People Daily.

Mwau’s explanation comes in the wake of claims that results of the Sars-CoV-2 tests carried out at the Lancet laboratory are not credible.

The controversy began early last month after two women received two sets of results from different laboratories with the one from Lancet showing they had Covid-19 while the repeat tests at Nairobi Hospital indicating that they were negative.

The same controversy resurfaced last week when Kiambu Central MP Jude Njomo narrated to  the National Assembly Health Committee how his family was forced to hurriedly bury their late mother Margaret Njomo last month after the Ministry of Health officials insisted she had tested positive.

Repeat test

Njomo said his mother had tested positive at a government facility, prompting them to go for a repeat test at Nairobi hospital which turned negative.

Last Thursday, Lancet chief executive Dr Ahmed Kalebi, insisted the Sars-CoV-2 PCR tests done at the facility at  a cost of Sh8,849 are 100 per cent sensitive and specific.

“We do appreciate the concerns raised by such discordance in results, which we’ve tried to explain scientifically through newsletters to our esteemed clients, medical colleagues taking care of them and the general public.

We’ve also shared independent research studies and evaluations which have demonstrated that positive test results from the Seegene Allplex™️ assay (similar to the one used at PLK) can be missed by other assays (such as those used by various labs in Kenya) and this is particularly so for cases that have low viral loads,” Dr Kalebi posted on his Facebook.

And joining the debate, Mwau who led the team of scientists nominated by the Kenya Medical Practitioners and Dentists Council to investigate tests conducted by Lancet, said the facility is only facing pressure from business rivals.

“After our investigations, it was established that Lancet is using high calibre machines and their staff are professionally qualified to carry out the tests. There is nothing fishy about the results from either Lancet or any other facility in the country,” said Mwau.

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