Effect of delay in processing and storage temperature on diagnosis of SARS-CoV-2 by RTPCR testing

A large number of new molecular or virology laboratories have been established to increase the testing capacity for SARS-CoV-2. Due to heavy workload, there is delay in testing of samples. In order to avoid the negative effect of delayed testing on RTPCR results guidelines are issued from WHO and CDC to transport samples in cold chain. However, in pandemic situations the recommended guidelines for transport and storage conditions are often compromised. This study was conducted to evaluate the effect of sample storage conditions at different temperatures on the results of RT PCR test.

Total 275 samples were included in this study, among these 126 samples tested positive and 149 samples tested negative. All samples were aliquoted into two and the aliquotes stored in duplicate at 4 ​°C and room temperature. All aliquots stored at both the temperatures were tested by RTPCR every 24 hours up to 5 days.

Diagnostic accuracy decreased from day1 to day 5 at both the storage temperatures i,e 4 ​°C and room temperature in comparison to the initial day results. Positivity decreased on an average of 9.02% at 4 ​°C and at 9.27% at room temperature per day. Among total 126 positive samples on an average false negative and failure of internal control at 4 ​°C and room temperature was 8.86%, 8.22% and 3.64%, and 4.12%, respectively. All the samples with CT value ​< ​30 remained positive at both temperatures up to 5 days. Few samples with >30 CT value showed variable results i.e. positive, negative or internal control failure from day 1 (2nd day after sample collection) onwards.

There was no significant difference between RT PCR results of samples stored at 4 ​°C and room temperature up to 5 days of collection. However internal control failure was more in samples stored at room temperature. Therefore, samples received without cold chain also may be processed by RTPCR and should not be rejected.