Improved matrix pooling

Real-life validation of a sample pooling strategy for screening of hepatitis C

OBJECTIVES

To test a real-life sample pooling screening strategy which contributes to increasing the diagnostic capacity of clinical laboratories and expanding access to massive screening of hepatitis C.

METHODS

After evaluating the sensitivity of the pooling strategy for seven different commercial assays which are used to determine the concentration of hepatitis C virus (HCV)-RNA in the plasma or serum, consecutive samples submitted for HCV diagnosis during the first 3 weeks of November 2021 were tested for HCV antibodies and, in parallel and in a blinded way, were pooled into 100 samples and tested for HCV-RNA. When the result was positive, a strategy to un-mask the positive(s) pool(s), which needed up to 15 total HCV-RNA tests, was used.

RESULTS

All platforms were able to detect the presence of HCV-RNA in a single sample from a patient with viremic HCV present in pools of up to at least 10 000 HCV-RNA-free samples. A total of 1700 samples (17 pools) were analysed, with an overall prevalence of anti-HCV and HCV-RNA of 0.24%. After pooling, we could detect all samples previously detected using standard diagnosis tests (reflex testing) with a specificity and sensitivity of 100% (CI, 99.78-100%). Given the median current prices of anti-HCV and HCV-RNA on the market in Spain as well as personnel costs, testing using the pooling strategy would have resulted in a save of 3320€.

CONCLUSIONS

Here, we demonstrated that by improving cost effectiveness, with no loss of sensitivity and specificity, the strategy of pooling samples may serve as an appropriate tool for use in large-scale screening of HCV.

Nested Group Testing Procedure

We investigated the false-negative, true-negative, false-positive, and true-positive predictive values from a general group testing procedure for a heterogeneous population. We show that its false (true)-negative predictive value of a specimen is larger (smaller), and the false (true)-positive predictive value is smaller (larger) than that from individual testing procedure, where the former is in aversion. Then we propose a nested group testing procedure, and show that it can keep the sterling characteristics and also improve the false-negative predictive values for a specimen, not larger than that from individual testing. These characteristics are studied from both theoretical and numerical points of view. The nested group testing procedure is better than individual testing on both false-positive and false-negative predictive values, while retains the efficiency as a basic characteristic of a group testing procedure. Applications to Dorfman's, Halving and Sterrett procedures are discussed. Results from extensive simulation studies and an application to malaria infection in microscopy-negative Malawian women exemplify the findings.

Sample pooling for SARS-CoV-2 RT-PCR screening

Objective

To evaluate the efficacy of sample pooling compared to the individual analysis for the diagnosis of coronavirus disease 2019 (COVID-19) by using different commercial platforms for nucleic acid extraction and amplification.

Methods

A total of 3519 nasopharyngeal samples received at nine Spanish clinical microbiology laboratories were processed individually and in pools (342 pools of ten samples and 11 pools of nine samples) according to the existing methodology in place at each centre.

Results

We found that 253 pools (2519 samples) were negative and 99 pools (990 samples) were positive; with 241 positive samples (6.85%), our pooling strategy would have saved 2167 PCR tests. For 29 pools (made out of 290 samples), we found discordant results when compared to their correspondent individual samples, as follows: in 22 of 29 pools (28 samples), minor discordances were found; for seven pools (7 samples), we found major discordances. Sensitivity, specificity and positive and negative predictive values for pooling were 97.10% (95% confidence interval (CI), 94.11–98.82), 100%, 100% and 99.79% (95% CI, 99.56–99.90) respectively; accuracy was 99.80% (95% CI, 99.59–99.92), and the kappa concordant coefficient was 0.984. The dilution of samples in our pooling strategy resulted in a median loss of 2.87 (95% CI, 2.46–3.28) cycle threshold (C_t) for E gene, 3.36 (95% CI, 2.89–3.85) C_t for the RdRP gene and 2.99 (95% CI, 2.56–3.43) C_t for the N gene.

Conclusions

We found a high efficiency of pooling strategies for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA testing across different RNA extraction and amplification platforms, with excellent performance in terms of sensitivity, specificity and positive and negative predictive values.