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The Germany Model of pool testing, India yet to take a call, sticks to antibody testing for COVID-19

  • TeamPresentMirror | Updated: April 7, 2020, 3:49 p.m.

India is still struggling with limited number of testing kits the country has.Through this Germany has been able to increase their testing capacity from 40,000 tests per day to as high as 3.5 lakhs tests per day without dampening the quality of the tests. India for the first time will attempt serological antibody tests.


Graphics Credits : Present Mirror

A nation of billion people require extensive testing which can cover the major population. India is still struggling with limited number of testing kits, the country has. The nation has so far followed the conservative testing strategy, cautiously and coherently trying to cover all those in need. India has a limited stock of 10 lacs PCR testing kits. But, how long till such strategies will stay? Is it time for the country to follow the more progressive ways like the Germany Model of pool testing for COVID-19?

The swab sample from mucous membranes of the nose or throat are collected in a buffer solution. This is called RT-PCR (reverse transcription polymerase chain reaction) procedure done by direct genome sequencing of SARS CoV-2 virus. The attempt is to make a mini pool of two or more, here lets consider three samples. The swabs, instead of placing in three separate containers, are placed in a single container of the same volume. This also doesn’t lead to dilution of sample as well as there is no decline in sensitivity found. If any pool tests positive, then patients of that pool can go for separate testing.Germany has tried and tested this methodology and have gained significant increase in results.

Image Credits: Michael Schmidt, Frankfurt Institute

The results obtained by Germany are very positive. The Frankfurt Institute did a field test on 50 tested patients. They made 10 mini pool of 5 samples each. Four samples were made to be of positive and 1 sample was made of negative patients. Always the pool of negative patients tested negative. Through this Germany has been able to increase their testing capacity from 40,000 tests per day to as high as 3.5 lacs tests per day without dampening the quality of the tests.

India has some reservations on this method of testing. “Efforts to increase test capacity by the ‘pooling’ of samples are being evaluated. This is not simple and needs the development and testing of optimization algorithms so that one positive in a large pool is not missed, for example”, said K. Vijay Raghavan, Principal Scientific Adviser, Govt. of India, on his twitter handle.

Israel used 64 patients for testing and got satisfactory results. “According to the new pooling approach that we have currently tested, molecular testing can be performed on a 'combined sample', taken from 32 or 64 patients. This way we can significantly accelerate the testing rate. Only in those rare cases, where the joint sample is found to be positive, will we conduct an individual test for each of the specific samples”, said Dr. Yuval Gefen, director of the Rambam Clinical Microbiology Laboratory. The researchers at Yad Hanadiv - The Rothschild Foundation in Israel found out, “On testing a pooling approach for the standard RT-qPCR test, we find that a single positive sample can be detected even in pools of up to 32 samples, with an estimated false negative rate of 10%. Detection of positive samples diluted in even up to 64 samples may also be attainable, though may require additional amplification cycles”. The research can be read here.

Till now close to 80,000 cases are tested in India and roughly 4,000 have been tested positive.The rate of positive cases to that of tested in INDIA is 0.02.The testing methods like that of Germany or Israel can be easily adopted in a populous country like India. For instance, if we implement the Israel method the mini pools of 32 swab samples can be tested at one go and then every octa pair can be tested separately. Considering the same rate of infection in 96 persons in 3 pools of 32 persons each, it would give approximately 0.6 persons positive per pool.This implies that in every 3 pools,one pool can test negative in one go. 32 people now are tested negative with just one kit. If we further divide the remaining 2 pools of 64 persons into sub pools of 8 persons each. Except 2 pools, remaining 6 pools will test negative. Again 48 persons are tested negative with 6 kits. Now those that are tested positive are a cluster of 16 persons which can be tested in 8 binary pairs followed by 4 individual testing. Overall, to test 96 persons 23 tests would be needed, four times lesser. This number like Germany can increase significantly if the sample space is more. This method could be used in testing asymptomatic individuals, which can help in saving a large number of kits.

India to rely on rapid antibody test kits as the first line of detection

Image Credits: Nirmidas Biotech

India for the first time will attempt serological antibody tests. This uses blood samples instead of nasal swabs. The test involves pricking a finger to collect blood samples and doesn’t require an expert to do it like RT-PCR, similar to a simple pregnancy test. There is an Ig(Immunoglobulin) G line, a control line, a IgM line and a negative line. Early infected asymptomatic patients show IgM antibodies and hence can be isolated as per procedure. This may help detecting asymptomatic individuals in their early stages itself. It takes around 4-7 days for patients to develop IgM anti bodies while several weeks to develop IgG antibodies, suggesting that asymptomatic patients diagnosed with IgG have already developed immunity against virus and are past the infection stage.

Indian Council of Medical Research (ICMR) in its press briefing said that the rapid testing kits could prove as a breakthrough when it comes to testing of hotspot areas.Those tested negative can be quarantined as a precaution. Henceforth, those who tested positive for IgM can further be tested by the RT-PCR test using swabs of the nasal or throat. This method takes just 15 minutes to give results. A Pune based start-up, is already producing mass number of kits on war footing.

It is high time India adopts a uniform, intelligent method for early detection. The country is still in stage 2, grappling with limited number of kits over a billion population. The Germany model of pool testing may prove out to be an elixir of hope to quench thirst for the cautiously wandering health system of India in the deserts of COVID-19.

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