- What is pooling of samples & how does it work? – A pooled testing algorithm involves the PCR screening of a specimen pool comprising multiple individual patient specimens, followed by individual testing (pool de-convolution) only if a pool screens positive. As all individual samples in a negative pool are regarded as negative, it results in substantial cost savings when a large proportion of pools tests negative.
- Limitations of pooling of samples – Pooling of samples is not recommended in areas or populations with positivity rates of >5% for COVID-19. Preferable number of samples to be pooled is five, though more than two samples can be pooled, but considering higher possibility of missing positive samples with low viral load, it is strongly discouraged to pool more than five samples, except in research mode. As per a study, pooling of samples should be used only in areas with low prevalence of COVID-19.
- Precautions to be taken – In areas with positivity of 2-5%, sample pooling for PCR screening may be considered only in community survey or surveillance among asymptomatic individuals, strictly excluding pooling samples of individuals with known contact with confirmed cases and health care workers (in direct contact with care of COVID-19 patients). Sample from such individuals should be directly tested without pooling.
Practice Question: Pooling of samples for COVID 19 testing has come up as a promising solution for increasing the number tests, however, the method has its own limitations. Discuss. – 200 words.