Pooled Sampling Increases COVID-19 Testing in Ghana
“We are pleased to inform you that after the recent COVID-19 test conducted, your results came out negative,” read a text message to Benedict Abbey. “Please do well to continue to strictly adhere to the precautionary protocols and we will get through this healthy and safe.”
Six days earlier Abbey had been tested for the virus after being traced and contacted by the Ghana Health Service when a colleague at his workplace tested positive for COVID-19. Waiting for the results while in isolation was agonizing.
“I was not able to sleep well. I was always thinking about the whole thing and I wondered what will happen if I tested positive,” says Abbey. “But after the results were released, I felt relieved and happy.”
Others have had different experiences while awaiting COVID-19 test result. Accra-based businesswoman who gave her name only as Sylvia was quarantined for two weeks alongside other passengers when she arrived from the United Kingdom in early March. “There were hundreds of us essentially in lockdown. We didn’t know when we would be able to leave. I was glad to be tested – and glad such measures were being put into place. But it took many days before I knew my situation. It was extremely stressful.”
Since detecting the first COVID-19 case on 12 March, Ghana Health Service has anchored the response on tracing, testing and treatment. Noguchi Memorial Institute for Medical Research, the country’s pre-eminent biomedical institution, was initially Ghana’s only facility able to test for COVID-19. But the Government, with support from the World Health Organization (WHO), Africa Centres for Disease Control and Prevention, and other partners, has since May expanded COVID-19 testing centres to nine other highly specialized laboratories.
Noguchi Institute is now working round the clock to carry out Polymerase Chain Reaction (PCR) for COVID-19. The PCR test directly detects the presence of the virus rather than the detecting antibodies, which would show the person has been previously infected with the virus.
As Ghana has ramped up contact tracing, the number of test samples has also increased. Already at capacity, working round the clock in 12-hour shifts, Noguchi Institute decided to deploy “pooled sampling” to meet demand. Each pool has 10 samples and 100 pools are tested at a time. Instead of testing one person at a time, samples from multiple individuals are put together and tested as one pool. If the pooled test comes back negative, everyone in the pool is declared negative. But if it is positive, each member of the pool is then retested individually for the infected person to be identified.
Pooled sampling has not only rapidly scaled up PCR testing capacity, but ultimately uses less testing reagents, and has shortened the results waiting time to two from around six days, helping to shift the backlog of samples for testing that have built up in the laboratories, and relieving overcrowded isolation centres.
“PCR gives us a good indication of who is infected. We can get in contact with people they’ve been in touch with so they can be quarantined too, just in case. So it helps to give a clearer picture of what’s happening,” says Prof William Ampofo, head of the Virology Department at Noguchi Institute.
Ghana has conducted over 370 000 tests between March and mid-July making it one of the countries in the WHO Africa Region with the most tests per 100 000 population.
Crucially, this type of testing helps the national COVID-19 response team better understand the spread of the disease and how to direct and adapt their response strategy.
“It gave us an idea about the level of community spread of the disease which was mainly in Greater Accra and the Ashanti regions,” says Dr Franklin Asiedu Bekoe, who heads the Disease Surveillance Unit at Ghana Health Service. “At the time we started picking cases which hitherto we would not think they had the infection.”
Dr Bekoe explains that about 55% of patients in the country are asymptomatic, “so they are not cases that would typically be picked at the hospital but because we are using this method of testing and enhanced surveillance which does not really rely on symptoms, we are able to get the cases in time and start early treatment.”
This method of COVID-19 testing can not only be cost-effective, it can also be used at points of entry, in areas with low prevalence of the virus as well as to test asymptomatic people, notes Dr Yahaya Ali Ahmed, a laboratory expert at WHO Regional Office for Africa. However, he points out that in areas with high COVID-19 transmission, pooled testing can give more positive results and reduce testing sensitivity due to dilution as specimens are grouped. In the WHO African Region, Ghana and Rwanda are currently using pool testing.
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