Coronavirus Outbreak Explained: What Is Pool Testing And Can It Expedite COVID-19 Detection In The Country?

New Delhi: “We have a simple message for all countries – test, test, test,” said Dr. Tedros Adhanom Ghebreyesus, Director General at the World Health Organisation (WHO) last month while chairing the daily media briefing. Highlighting the importance of testing large number of people, he said that more test will enable identifying, isolating and treating the infected person and their contacts in order to protect the others from getting infected and thus breaking the chain of transmission of COVID-19. While WHO has urged the countries to conduct mass testing for coronavirus, short supply of testing kits has been a problem, as per experts. Therefore, in a bid to increase the number of samples tested using the limited testing kits available, experts and policymakers have called for ‘pool testing’ which was earlier used to detect large outbreaks and invisible community transmission, such as of Trachoma, HIV (Human Immunodeficiency Viruses), the virus that causes AIDS (Acquired Immunodeficiency Syndrome) and other communicable diseases. But what is pool testing and how effective is it likely to be? Experts explain all about it.

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What Is Pooled Testing?

Dr. Ramana Dhara, Professor at Indian Institute of Public Health (IIPH), Hyderabad explains pool testing as a process that involves swab samples from mucous membranes of the nose or throat of two to five persons are combined in a test tube and tested for SARS-CoV-2, the virus that causes COVID-19 using the real-time reverse transcription-polymerase chain reaction (RT-PCR) procedure. RT-PCR is used for detecting infection or the presence of specific genetic material from any pathogen or virus. If the result is negative, all individual samples in that pool are regarded as safe while if a pooled sample tests positive, each person in the pool is tested individually to find out who is affected.

According to a research paper published on the Bulletin of the WHO titled ‘Pooled-sample analysis strategies for COVID-19 mass testing: a simulation study’, pool testing can enhance pandemic surveillance in settings with low to moderate prevalence of infection. The authors of the paper, Andreas Deckert, Till Bärnighausen, and Nicholas Kyei of Heidelberg Institute of Global Health, Heidelberg University, Germany said that group sizes up to 25 samples in a population of 150 000 could be used for pool testing. However, the Indian Council of Medical Research (ICMR) suggests that not more than five samples should be pooled. Dr. Ambarish Dutta, Associate Professor, Indian Institute of Public Health (IIPH) Bhubaneswar, said that with a higher number of pooled samples there are higher possibilities of missing positive samples with a low viral load in the pool of negative dominant samples.

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Pool Testing Can Help Overcome The Shortage Of Test Kits

Dr. Dhara asserted that pool testing helps in reducing the total number of testing kits used for testing communities. He said,

When there is a limited testing capacity, multiple samples are pooled and tested to save on the number of tests. It’s a community screening strategy which helps to implement timely infection control measures. It also saves a lot of resources — time, cost and manpower.

He also highlighted that if the viral load in an area increases which means the number of infected patients increases, then pool testing will not be as effective and individual testing needs to be done.

Therefore, the biggest drawback of the pool testing, according to Dr. Dhara is that it can be used only at those places where the infection rate is low. He also said that pool testing can miss individuals in whom the virus has not started developing yet.

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Pool Testing In India

According to Dr. Rakesh Sahay, Endocrinologist and Diabetologist, and Professor at Osmania Medical College in Hyderabad, Uttar Pradesh (UP) and Andaman and Nicobar Islands are the first areas to start pool testing after the ICMR assessed the feasibility of this strategy and laid out an advisory about it. The feasibility study was conducted at ICMR’s Virus Research & Diagnostic Laboratory (VRDL) at King George’s Medical University (KGMU), Lucknow. The study demonstrated performing real-time PCR testing for COVID-19 with multiple samples (upto five) is feasible when the prevalence rates of infection are low. In its advisory, ICMR said,

Pool testing may also be used for community survey or surveillance among asymptomatic individuals, but is strictly prohibited in cases of individuals with known contact with confirmed cases and healthcare workers (in direct contact with the care of COVID-19 patients).

In the last 10 days, UP has ramped up its testing capacity because of pool testing technique. While the state was earlier criticised for not testing enough, is now testing more than 3,500 samples per day which is currently highest in the country, according to the Directorate of Medical and Health Services, UP. Chief Secretary of Andaman and Nicobar Islands Chetan B Sanghi tweeted recently.

According to Dr. Dhara, Maharashtra has recently received approval from the Central government for using pool testing and the states of Odisha, Rajasthan, West Bengal and Gujarat may soon follow, to increase testing and curb the spread of infection.

In the context of COVID-19, pool testing was proposed in Germany and Israel. The United States of America and Italy are also using pool testing strategy to increase testing.

According to Dr. Dhara, India urgently needs to scale up its testing in order to tackle the current pandemic. In India, testing has increased from 5,000 on April 1 to about 30,000 a day within three weeks, this number has to increase exponentially to find out if there is an undetected infection in the community. As of April 23, about five lakh samples have been tested, according to ICMR but this is not enough for a country with a population as big as more than 130 crore, say Dr. Sahay.

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