Store positive Covid-19 samples for 30 days before destroying: ICMR to govt labs

The ICMR on Thursday advised government laboratories to retain all samples testing positive for coronavirus infection for a minimum of 30 days before destroying them.

In its 'Guidelines for storage of respiratory specimens collected for Covid-19 diagnosis by RT-PCR platforms in government laboratories', the apex health research body said appropriate procedures to disinfect all samples prior to disposal must be followed and the labs should keep a record of the destruction. According to the guidelines, all samples being stored for a long-term must be appropriately labelled indicating laboratory identifiers, date of collection and must be kept in properly functioning -80ºC deep freezers. A proper inventory (preferably electronic) of stored samples should be essentially maintained.

With the surge in testing across the country, the number of tested samples has gone up considerably, the ICMR said as it advised laboratories that are serving as validation centres for Covid-19 diagnostic kits to preserve adequate numbers of positive and negative samples to prepare appropriate panels for validation.

There is a need to retain clinical specimens or a subset of the clinical specimens for various purposes such as performing additional tests, for quality control purposes or for use as control materials to assess newer diagnostic tests. "In addition, a laboratory may need to store specimens for projects aimed at studying genomic epidemiology of the SARS-CoV2 virus across regions and over time," ICMR said.

A government laboratory may decide on the number of positive and negative samples to retain in the long term based on the availability of freezer space as well as perceived research agenda of the laboratory for Covid-19 in the future, the guidelines stated. If the number of samples tested positive at a laboratory is considerably large and the laboratory is unable to retain all positive samples beyond 30 days, a minimum of 10 per cent of all positives detected at the laboratory in a month or 40-50 positives preferably with equal numbers of high, moderate and low viral load should be stored for a period of one year at the least.

A single aliquot of a positive sample may be retained taking into account freezer space availability at the laboratory, it said.

Considering that the number of samples tested negative at each laboratory will vary depending on the load and testing capacity of the laboratory, a minimum of 50 samples or 1-2 per cent of such samples tested over a month, whichever is smaller should be retained at the testing laboratory for a period of one year. According to the guidelines, all labs will send five random positive and as many negative samples per month to quality control labs.

ICMR has mapped Covid-19 testing labs to different quality control labs. All testing labs should liaise with the recommended quality control labs and will ensure regular participation in the activity. All testing labs will ensure storage of samples at -80̊ C and will ensure regular monthly transfer to quality control labs. "Don't forget to include your lab name and sample ID. While shipping, place samples in screw capped vials and proper biosafety and biosecurity precautions should be followed," the ICMR said. In case of any discordance, additional five positive and three negative samples will need to be sent for quality control check. If quality control results are concordant, the samples may be destroyed and labs will keep a record of destruction.