Introduction: Highly sensitive reagents for detecting SARS-CoV-2 antigens have been developed for accurate and rapid diagnosis till date. In this study, we aim to clarify the frequency of false-positive reactions and reveal their details in SARS-CoV-2 quantitative antigen test using an automated laboratory device. Methods: Nasopharyngeal swab samples (n = 4992) and saliva samples (n = 5430) were collected. We measured their SARS-CoV-2 antigen using Lumipulse® Presto SARS-CoV-2 Ag and performed a nucleic acid amplification test (NAAT) using the Ampdirect™ 2019 Novel Coronavirus Detection Kit as needed. The results obtained from each detection test were compared accordingly. Results: There were 304 nasopharyngeal samples and 114 saliva samples were positive in the Lumipulse® Presto SARS-CoV-2 Ag test. All positive nasopharyngeal samples in the antigen test were also positive for NAAT. In contrast, only three (2.6%) of all the positive saliva samples in the antigen test were negative for NAAT. One showed no linearity with a dilute solution in the dilution test. Additionally, the quantitative antigen levels of all the three samples did not decrease after reaction with the anti-SARS-CoV-2 antibody. Conclusions: The judgment difference between the quantitative antigen test and NAAT seemed to be caused by non-specific reactions in the antigen test. Although the high positive and negative predictive value of this quantitative antigen test could be confirmed, we should consider the possibility of false-positives caused by nonspecific reactions and understand the characteristics of antigen testing. We recommend that repeating centrifugation before measurement, especially in saliva samples, should be performed appropriately.
Vibrio parahaemolyticus organisms cause acute gastroenteritis in humans. These bacteria are natural inhabitants of both marine and estuarine ecosystems. In the present study, we investigated the effectiveness of a non-selective enrichment of sediment samples with sodium chloride prior to selective enrichment with alkaline peptone water for a better recovery of V. parahaemolyticus. Sediment samples were collected with or without 1% NaCl from the river Buriganga, located besides Dhaka city and about 400 km away from the Bay of Bengal, and from the estuary of the river Karnaphuli which flows into the Bay of Bengal. Very small number of V. parahaemolyticus (<30 MPN/g) were detected in the sediments of both river and estuary, where NaCl was not added. On the other hand, the number of V. parahaemolyticus increased to more than 40 times (1500 MPN/g) in the river and 32 times (960 MPN/g) in the estuary where NaCl were added. River sediment sample contained the serotype O9:K41 of V. parahaemolyticus and the estuarine sample contained O3:K41 and O3:KUT Our results suggest that a pre-enrichment of environmental samples with 1% NaCl helps V. parahaemolyticus to survive for at least 7 days until they are enriched with alkaline peptone water, for better recovery.
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