Point-of-Care RSV Assay Holds Up to Lab Testing in Older Adults

The point-of-care Xpert Xpress Flu/RSV test appeared nearly as accurate as routine real-time RT-PCR for detecting respiratory syncytial virus (RSV) infections in older adults, a Dutch study found.

For the 35 of 758 respiratory samples tested that turned up positive for RSV by either the Xpert Xpress Flu/RSV assay or real-time RT-PCR, the only discordant results were two negative results by the point-of-care assay and three by lab-based PCR testing, reported Joanne Wildenbeest, MD, PhD, of the University Medical Center Utrecht in The Netherlands, and colleagues.

The two tests had 90.9% positive percentage agreement (95% CI 76.4-96.8) and 99.7% negative percentage agreement (95% CI 99.0-99.9), with an overall rate of agreement of 99.3% (95% CI 98.5-99.7), the authors wrote in The Journal of Infectious Diseases.

No significant differences in positive percentage agreement were observed by gender, age, comorbidities, symptom duration, or level of care.

“The assay is fast and easy to use and therefore has the ability to improve patient management and outcomes,” the researchers concluded.

Laboratory-based real-time RT-PCR has been the “gold-standard” for detecting RSV but has long turnaround times for results. Molecular point-of-care tests like the Xpert Xpress test use the same nucleic amplification as RT-PCR and deliver results in about 30 minutes, which has been “associated with a significant reduction in hospital length of stay, testing costs, and isolation time,” Wildenbeest’s group wrote.

Their study homed in on the ambulatory older adult population to confirm sensitivity in this population, which generally has a lower viral load than seen in young children, “which could result in suboptimal sensitivity of RSV diagnostics,” they pointed out.

For their study, Wildenbeest and colleagues examined data on 758 respiratory samples provided by 561 home-dwelling adults ages 60 and older. They were recruited through general practices in Belgium, the United Kingdom, and The Netherlands via the Respiratory Syncytial Virus Consortium in Europe (RESCEU). Participants had at least one acute respiratory tract infection during two RSV seasons (2017-2018 and 2018-2019), although disease severity covered the range from mild to severe.

Participants were contacted weekly to inquire about their symptoms. Samples were collected by a trained study team member who visited homes to obtain two nasopharyngeal minitip flocked swab samples at a median of 4 days after symptom onset.

The first collected swab was stored in a universal transport medium to be analyzed by the Xpert Xpress Flu/RSV within 24 hours. The second was placed in aliquots at -80^°C for real-time RT-PCR testing later.

A little more than half of participants were women (54%), the median age was 75, and about 38% had comorbidities.

Respiratory episodes remained mostly mild, but 170 participants required medical attention without hospital admission and four were hospitalized.

Notably, the only five discordant results between the two tests all had low viral loads on both assays (≤10³ copies per mL or cycle threshold ≥34), which is around or below limits of detection of both tests, the researchers noted.

The authors acknowledged several limitations to the data, including the lack of consistent viral transport media and storage conditions across both swabs tested, potentially minimizing viral load. The number of positive samples analyzed were also low.