We ‘pool’ coronavirus samples to test 1,000s at a go; we've done 30,000 since Sunday – Noguchi

The Noguchi Memorial Institute for Medical Research (NMIMR) has explained that it uses a method called “pooling” to test thousands of COVID-19 samples at a go, thus, making the facility’s testing abilities very efficient.

Prof William Ampofo, Head of Virology at the Noguchi Memorial Institute for Medical Research, which is leading and coordinating the entire testing programme, explained to journalists on Wednesday, 22 April 2020 at a press briefing organised by the Ministry of Information in Accra, that the pooling method has been handy in testing several thousands of samples within a short time.

“Now, if you’ve been to Noguchi recently, you’d seen the white building in front of our institute. This building actually facilitates the process; it has enabled us to test thousands of samples within the recent couple of weeks”, he said.

“How have we done these testing? As you have heard, you cannot see a virus, so, to test for the virus, we actually extract the inner components of the virus, and it’s called ribonucleic acid (RNA). Now, how do we collect the sample or what kind of sample do we use for the testing? Because this is a respiratory virus, we look for the virus in the respiratory pathway, OK.

“So, we take swabs from the nose, swabs from your throat; we also take sputum which you bring out from the throat and then we also have another method where we introduce saltwater through your nose and you blow it out, it’s called nasal lavage. So, these are the four types of specimen or samples we have used in Ghana to test for the coronavirus”, he explained.

Continuing, Prof Ampofo said: “When these samples arrive at the lab, whether it is Kumasi or Noguchi or the VC or the Public Health Reference Lab, we go through a process to enable us utilise the reagents or chemicals in a very efficient manner. We simply pool the samples.

What is pooling?

“Pooling just means that if you have 1,000 samples, you put them in pools of ten and, therefore, you test, at a time, 100 pools. So, instead of testing 1,000 samples, you actually test 10,000 samples. This simple arithmetic is what some people cannot do. If you want to understand how we are able to utilise our existing facilities using a method that was derived in 1945 for screening samples right from the Blood Bank, this is a very efficient way of proceeding”, he explained.

Prof Ampofo said: “The other thing we have done is that; to ensure that we are not diluting the samples when we mix 10 of them together, we simply put one positive sample, which was at the limit of the detection of our system, and diluted nine other samples, which were negative, therefore, we would determine that if we pooled one, two, three, four, five, six, seven, eight, nine, ten together, we are still able to detect the first sample, which is at the limit of positive detection”.

Again, he noted, “with our partners, we have the kind of equipment to be able to do this detection”, adding: “So, when we started, we realised that as the number grew; we were actually pooling five samples and then we changed to a pool of ten samples and this simple protocol was followed by LIS and KCCR and, of course, it’s now adopted by colleagues here at PHRPSD”.

“So, in a nutshell, you can understand that it is not impossible to have tested 68,000 samples as His Excellency the President reported when he addressed all of us. Actually, since he addressed us, we have tested close to 30,000 samples; again, using the same method. Because each time we do 10,000 samples, it’s actually a multiplication of a simple initial number. So, please, do not be surprised if, in the next couple of days, you hear that we have tested 100,000 samples in Ghana. It’s just a matter of multiplication and addition.

“Now, we don’t just test, each test that is done follows policy control tests as indicated by the manufacturer”, he noted.