Utility of quantitative loop mediated isothermal amplification (qLAMP) assay for the diagnosis of invasive pneumococcal disease (IPD)

Purpose: Quantitative LAMP (qLAMP) assay is one of the recent and emerging diagnostic tests for infectious diseases. Only a few studies exist comparing this assay with quantitative real-time PCR (qPCR) for the diagnosis of invasive pneumococcal disease (IPD). Aim: To compare the diagnostic performance of qLAMP assay with qPCR targeting autolysin gene for the diagnosis of invasive pneumococcal disease. Methods: Ninety six blood samples and 73 CSF samples from patients clinically suspected with community acquired pneumonia and acute meningitis were tested by qPCR and qLAMP assays using previously published primers and protocols. The qPCR was considered as the gold standard test and the diagnostic performance was assessed by calculating sensitivity, specificity, positive and negative predictive values, and kappa coefficient for the level of agreement between the tests. Chi-squared/Fisher exact test was used to compare categorical variables (positive/negative). Results: Thirty two blood samples and 22 CSF samples were positive by qPCR while 24 and 20 samples were positive by qLAMP assay respectively. The sensitivity of qLAMP assay was only 86.4% and 75% when tested on CSF and blood samples respectively. However, the qLAMP assay was in substantial to almost perfect agreement when compared with qPCR. The results were statistically significant in both sample types (P < 0.001). Conclusions: The performance of qLAMP assay can vary based on the specimen type. It has very high specificity and had substantial to almost perfect agreement, and thus may be an alternative to qPCR for the diagnosis of IPD.