Lung ultrasonography unmasking the asymptomatic SARS-CoV-2 carrier

Dear Editor,

The 11th of March of 2020, the World Health Organization declared a pandemic caused by a novel coronavirus, named Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), with the spread to more than 180 countries, 37,418,821 cases confirmed and 1,076,818 deaths caused.¹

The disease severity spectrum is believed to be broad. Interestingly, according to different studies, many patients (40-80%) are asymptomatic at the time of testing,² and only few of them (0-10%) went on to develop symptoms. Researchers report that asymptomatic COVID-19 is more common among women and younger adults (median age 37) that could shed the virus for a median of 8 days.³

In this emergency, is critical the ability to quickly confirm these asymptomatic carriers to avoid transmission of the virus, especially in healthcare workers. For this reason, screening them for symptoms or unprotected exposures might not be effective.

We herein report the case of a 31-year-old woman with no significant past medical history. She is an emergency physician who had been working in the front line of our hospital treating Coronavirus Disease (COVID-19) patients since the beginning of the pandemic. She reported a close contact with a just confirmed COVID-19 patient in the household setting.

The physical exam was unremarkable, with normal lung auscultation. At that moment, a Point-of-Care Lung ultrasonography (LUS) was performed with a hand-held ultrasound device (Butterfly IQ – Butterfly Network, Guilford, CT, USA), following a twelve-zone scanning scheme of the anterior, lateral and posterior chest, showing a thickened and irregular pleural line with prominent B-lines in the left posterior lobe. The rest of the lung ultrasound showed an A-line pattern. A nasopharyngeal swab for SARS-CoV-2 test was done, being negative. Laboratory tests were unremarkable. Given her absence of symptoms, she refused to have a chest Computed Tomography (CT).

One month later, as a serology surveillance strategy was implemented at our hospital, she had a serology test with the presence of positive SARS-CoV-2 IgG and negative IgM (Chemiluminescence and Enzyme-Linked Inmmunosorbent Assay). At this moment LUS was repeated, with an improvement of the previous findings. Three months after the start of the pandemic, she remains asymptomatic.

There is growing literature regarding the usefulness of diagnostic imaging on COVID-19. A previous study found that chest CT scan abnormalities had a high sensitivity for diagnosis of COVID-19 patients,⁴ suggesting that CT scan should be considered as a screening tool, especially in epidemic areas with high pre-test probability.

However, for these asymptomatic carriers, radiation exposure and overuse of health care resources, or lack thereof ability to get a CT scan seems to overshadow the need.

LUS is innocuous, quickly completed following simple and easy to apply protocols and whose findings correlate excellent with CT scan.⁴

Prioritizing healthcare workers for Reverse Transcription Polymerase Chain Reaction (RT-PCR) test, serology test in addition to serial LUS exam, during these surveillance strategy campaigns, could more accurately diagnose the stage or time course of the COVID-19 infection, overcoming some of the limitations of the RT-PCR and serologic tests.⁵ This is essential, as especially false negative results could cause false reassurance, behaviour change and disease spread.

The main limitation is that LUS findings are not specific to SARS-CoV-2 infection, and the same abnormalities might be seen in other interstitial syndromes triggered by different causes that must be considered. However, in epidemic areas, these positive LUS features, even in asymptomatic or negative RT-PCR can still be highly suggestive of COVID-19 infection.

We want to share our case report findings, given the urgent need for different diagnostic strategies in order to identify asymptomatic SARS-COV-2 carriers, especially healthcare workers, and mitigate community transmission of SARS-CoV-.

In conclusion, the usefulness that LUS presents in this COVID-19 pandemic, especially in unmasking asymptomatic carriers is worth consideration. Further work integrating it in different surveillance strategies are needed before the release of the lockdown measures.

Authorship

All authors have contributed equally to this work.