A small-scale external quality assessment for PCR detection of group B streptococcus in China

Group B streptococcus (GBS) is considered a leading cause of maternal and infant morbidity and mortality. Molecular diagnosis is a routinely used approach for GBS screening to protect pregnant women and prevent early-onset GBS neonatal disease. We identified issues and guarantee the dependability of GBS molecular diagnosis by an external quality assessment (EQA) scheme. The EQA panel comprised eight samples spiked with 10-fold dilutions of GBS suspension (20–2,000,000 copies/ml), and 2 negative control samples. The panels were coded randomly and distributed to participating laboratories for GBS detection. In total, 44 participating laboratories submitted results with eight commercial GBS PCR assays and one in-house assay. Among them, 36 obtained an acceptable or higher performance score, while 8 required improvement. Among the 440 results returned, 62 (14.1 %) were incorrect, including 5 false positives and 57 false negatives. Our small-scale EQA showed that most participating laboratories have reliable diagnostic capacities for GBS PCR detection. Nonetheless, further improvements in the detection performance of some laboratories are required, particularly with low-concentration samples. Our survey also reinforces the use of EQA as an essential tool to evaluate the overall proficiency of clinical laboratories.