In our study, more than two-thirds of asymptomatic older patients with SARS-CoV-2 infection showed signs of pulmonary involvement evaluated by lung ultrasound. Asymptomatic patients were more likely female, with a lower burden of comorbidity, usually showing unilateral interstitial involvement. As expected, overall mortality rate of asymptomatic patients was lower than symptomatic patients but, moving from the lowest to the highest LUS score tertile, their mortality rate showed a significant, progressive increase, typically in frail and pre-frail patients. Although older individuals suffering from COVID-19 represent the prototype of patients most at risk for adverse outcomes, to our knowledge, no previous studies have attempted to assess LUS artefacts and their relationship with a mid-term mortality risk in asymptomatic oldest patients.
It is well-established that a proportion of patients with COVID-19 without symptoms show HRCT signs of acute pneumonia; however, less is known about the prognostic impact of these findings in older frail patients, since they usually face disproportionate non-typical symptoms and an increase excess mortality after hospital discharge which is not completely understood,(8)(9). In the current study we hypnotized a crucial role of asymptomatic pneumonia evaluated with LUS, in the mid-term course of the disease in this particular class of frailest individuals with SARS-CoV-2 infection.
Lung ultrasound as been proved to be an important tool for interstitial lung evaluation of COVID-19 pneumonia and in the follow-up of the disease(21). In COVID-19, we typically see various grades of multiple B-lines with patchy distribution. B-lines can be separated or coalescent, including pictures of sonographic ‘white lung’(22). In agreement with Volpicelli et al(11), in our study at least three B lines and a fragmented pleural line were the most frequent ultrasonographic findings, both in asymptomatic and symptomatic patients. In our study, asymptomatic patients were more likely to present unilateral involvement, as first described by Shi el al.(3), who found unilateral, multifocal ground glass opacities at Chest CT. This finding is particularly of interest in the low care hospitals and nursing homes, where an accurate risk stratification is crucial to decide which older patients need to be transferred to a hospital or could be treated in the same setting. As expected, we found a significantly higher LUS score of aeration in symptomatic patients compared to asymptomatic pairs. In other words, patients with respiratory symptoms, showed a higher number of diffuse, bilateral B-lines compared to the asymptomatic ones, thus confirming an increased interstitial pulmonary damage.
In the current study we found a high prevalence of comorbidities, especially cardiovascular and chronic respiratory diseases. Consistent with previous studies(23), patients with severe COVID-19 manifestations showed a higher prevalence of cardiovascular disorders, compared to asymptomatic, although not reaching the statistical significance. Somewhat surprisingly, asymptomatic patients were older and frailer than those symptomatic; however, this result need to be contextualized in the clinical setting where the asymptomatic patients came from. Indeed, asymptomatic patients were residents of a nursing home temporarily transferred to a COVID-19 low care unit for clinical observation, while symptomatic patients were hospitalized in an acute care geriatrics unit. Although the prognostic role of multimorbidity and frailty is still debated(24), as a fact, older people living in nursing homes are commonly oldest with various degree of disability, needing assistance in basic activities of daily living.
Given that older individuals may present non-specific LUS pattern, such as localized B lines or pleural thickening due to pre-existing fibrosis(25),(26), we performed a concordance analysis by estimating the correlation of LUS findings and HRCT features in the acute geriatric ward. As expected, we found a a high proportion of agreement in terms of B-lines, pulmonary consolidations and pleural effusions, consistent with a recent paper by Nouvenne et al(12), in which the significant correlation between HRCT and LUS findings in COVID-19 was firstly reported.
During the three-month post-discharge follow-up, fourteen symptomatic and eleven asymptomatic patients deceased, yielding a worrying residual mortality of 24%, significantly higher than previous reports(27),(28), where a 2–5% mortality was recorded. However, in our study we aimed at focusing on the outcomes in the oldest individuals and patients severely disabled living in nursing homes, thus explaining this substantial difference. Noteworthy, after categorizing LUS score by tertiles, patients with the highest LUS score had two and three-times higher mortality compared to those of the lowest tertile, in symptomatic and asymptomatic patients, respectively. This result is not surprising since various studies have reported the post COVID-19 progression to lung fibrosis in older patients(29),(30), and a recent study by Somani et al(28), showed that the most common cause for re-admission at hospital after COVID-19 was respiratory distress, typically in comorbid patients.
Asymptomatic patients reported a lower overall mortality, facing most often a reduced interstitial damage detected by LUS score and decreased levels of inflammatory markers compared to symptomatic counterparts. Indeed, the overall lower mortality of asymptomatic patients largely depends on the fact that the majority were in the lowest tertile with half mortality than those with symptoms. On the other hand, mortality risk of asymptomatic patients overcome that of symptomatic in both the second and third LUS score tertiles (35.3% vs 22.2% and 66.7% vs 48.5%, respectively). One of the most interesting results emerging from our study is the demonstration of the complex interaction between frailty and morpho-functional pulmonary impairment in COVID-19 patients, regardless their clinical presentation. Hence, we recorded a higher mortality in pre-frail and frail patients in both symptomatic and symptomatic patients as compared to robust individuals; this result is in line with a recent multi-centre cohort study reporting an increased likelihood of adverse outcomes in patients with CFS score from 4 to 9(31). Interestingly, we found that a bilateral diffuse interstitial damage may act as a mortality-multiplying risk factor in frail patients, doubling the 3-months mortality moving from the lowest to the higher LUS score tertile.
In conclusion, the current study offers some important insight into the clinical status of asymptomatic COVID-19 older patients, highlighting the prognostic role of LUS evaluation in these individuals, regardless their clinical presentation. Given that frail patients often show non-typical COVID-symptoms and are the most at risk for poor outcomes, the utilization of LUS could guide the clinician in the decision-making process and direct an early-stage COVID-19 therapeutic management. However, the generalization of these results is subject to certain limitations. Firstly, as previously mentioned, due to a small sample size, the findings might not be conclusive; therefore, further prospective analyses in larger cohorts of older patients are needed to confirm these results in asymptomatic patients. Secondly, the study population accounts for two different clinical settings and, some significant differences between the two populations (i.e., age and ADL score) might be biased. Thirdly, in agreement with the current guidelines, we did not performed HRCT to asymptomatic patients; therefore, despite the exclusion of patients with a known history of chronic interstitial disease or pulmonary fibrosis, we cannot exclude an overdiagnosis of COVID-19 pneumonia in asymptomatic subjects, being the B-lines an indirect, non-specific sign of interstitial involvement. Notwithstanding, in the concordance analysis carried out in symptomatic patients, we confirmed a high proportion of agreement between the two techniques.