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The Simplexa COVID-19 / Flu A/B & RSV Direct is a real-time RT-PCR assay intended for use on the LIAISON MDX instrument for the simultaneous in vitro qualitative detection and differentiation of nucleic acid from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A (Flu A) virus, influenza B (Flu B) virus and respiratory syncytial virus (RSV) in nasopharyngeal swab and anterior nasal swab specimens from individuals with signs and symptoms of respiratory tract infection. Clinical signs and symptoms of respiratory tract infection due to SARS-CoV-2, influenza A, influenza B, and RSV can be similar.

The Simplexa COVID-19 / Flu A/B & RSV Direct assay is intended for use as an aid in the differential diagnosis of SARS-CoV-2, influenza A, influenza B and RSV infections if used in conjunction with other clinical and epidemiological information, and laboratory findings. SARS-CoV-2, influenza A, influenza B, and RSV viral RNA are generally detectable in nasopharyngeal swab and anterior nasal swab specimens during the acute phase of infection. This test is not intended to detect influenza C virus infections.

Positive results are indicative of the presence of the identified virus, but do not rule out bacterial infection or co-infection with other pathogens not detected by the test. The agent(s) detected by the Simplexa COVID-19 / Flu A/B & RSV Direct real-time RT-PCR assay may not be the definite cause of the disease. Negative results do not preclude SARS-CoV-2, influenza A, influenza B, or RSV infection and should not be used as the sole basis for patient management decisions.

The Simplexa™ COVID-19 & Flu A/B & RSV Direct assay is a qualitative, multiplex real-time reverse transcription polymerase chain reaction (RT-PCR) test intended for the simultaneous detection and differentiation of RNA from SARS-CoV-2, Influenza A, Influenza B, and Respiratory Syncytial Virus (RSV) in nasopharyngeal swabs (NPS) and anterior nasal swabs (NS) in UTM/UVT and M4RT specimen transport media. The assay is performed on the LIAISON® MDX Instrument using a Direct Amplification Disc (DAD) format, enabling sample-to-answer processing without separate nucleic acid extraction.

The LIAISON® MDX Instrument is a benchtop real-time PCR thermocycler that utilizes a self-contained, single-use direct amplification disc (DAD) to process samples. It performs thermal cycling and real-time fluorescence detection using optical detection modules, each with specific excitation and emission wavelengths. The instrument includes a laser enclosed in a laser product housing, with integrated hardware and software interlocks to ensure user safety. It is operated via a USB connection to a dedicated computer running the LIAISON® MDX Studio software.

The LIAISON® MDX Studio software controls the instrument and provides a user interface for assay setup, execution, and result analysis. The software automatically interprets results for in vitro diagnostic (IVD) assays using pre-defined assay definitions encoded in barcode inserts included with the assay kits. It performs spectral compensation, verifies internal control amplification, and checks for sufficient sample volume prior to amplification. The software also includes user authentication, audit logging, laboratory information system (LIS) connectivity, and cybersecurity features.

The assay kit includes single-use reaction mix vials, a positive control pack with inactivated viral particles in transport media, and the Direct Amplification Disc consumable, which supports up to eight simultaneous reactions.

The assay format is designed for direct amplification, with 24 single-use reaction mix vials per kit. The required sample volume input is 50 µL. The reaction mix is provided in single-use vials and includes DNA polymerase, reverse transcriptase, RNase inhibitor, primers, probes, and encapsulated RNA templates. The buffer component in the reaction mix maintains optimal pH and ionic strength to support enzyme activity and amplification efficiency throughout the RT-PCR process.

The assay includes an encapsulated RNA internal control (RNA IC) in each reaction to monitor for potential RT-PCR inhibition or process failure. The RNA IC is derived from bacteriophage MS2. This non-target RNA is co-amplified with the assay's viral targets and detected independently using post-amplification melting curve analysis. The presence of the RNA IC in a negative specimen confirms that the amplification process functioned as expected, while its absence—along with no target detection—results in an invalid outcome. Detection of the RNA IC is not required in the Positive Control but is expected in the No Template Control (NTC) to verify assay validity.

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