Clinical and CT findings of COVID-19: differences among three age groups

At present, the outbreak of the novel coronavirus pneumonia (coronavirus disease 2019, COVID-19) has become a public issue all over the world [1]. By April 24, 2020, more than 2,600,000 people have been diagnosed with COVID-19 [2], and it seems likely that the virus continues to spread. Transmission of COVID-19 through droplets, airborne and physical contact from infected (but not necessarily symptomatic) people, along with the frequent antigenic mutation of the virus make people more easily infected [3‐5], and all these factors make it too difficult to control. The incubation period of COVID-19 is usually 2 to 7 days (median 4 days), and can reach up to 24 days [6]. Official WHO data showed that the overall case fatality rate of COVID-19 in China was 5.51% (4642 deaths among 84,311 confirmed cases) [2], which actually might be even lower. Early isolation, early diagnosis, and timely treatment can lower the mortality effectively [6].

The main clinical manifestations of COVID-19 include fever, cough and fatigue. Some patients are presented with stuffy nose, shortness of breath, sore throat and sore muscles [7, 8]. The diagnostic golden standard of COVID-19 is the real-time reverse transcriptase polymerase chain reaction (RT-PCR) test [9], but with low sensitivity [10]. Meanwhile, too many patients are waiting for RT-PCR test due to the insufficient number of nucleic acid detection kits produced by enterprises in such a short time. CT scan is convenient, sensitive and fast, which serves as an important tool for screening, preliminary diagnosis and severity assessment of COVID-19.

Several studies have shown certain specificities of lung CT images in patients with COVID-19 [11, 12], which provided a reliable basis for diagnosis of the disease. Pan [13] et al. summarized CT data of 63 patients, exhibited as patchy consolidation, patchy/punctate ground glass opacities (85.7% of cases), ground glass nodules (22.2%), irregular solid nodules (12.7%) and fibrous stripes (17.5%). However, CT manifestations of COVID-19 are diverse, not all patients’ image performances are typical, pulmonary infection may involve one or more lobes simultaneously, with single, multiple or diffused lesions.

At present, there are few reports about clinical and CT features among different age groups of patients with COVID-19. Whether three age groups possess their own characteristics (including clinical manifestations, laboratory test results and CT features) remains ambiguous. Therefore, the purpose of this study is to analyze the clinical and CT features of patients with COVID-19 in three age groups, so as to better understand the characteristics of COVID-19 and better guide clinical diagnosis and treatment of this infectious disease.

Of all patients, 114 out of 307 (37.1%) had a history of epidemiological exposure. Fever, cough and fatigue are typical clinical manifestations of COVID-19. Other clinical manifestations include sore throat, chest tightness or pain, dizziness, aching muscles, hyperpnea and nasal stuffiness. Wang et al. [16] reported common symptoms of 138 patients were fever (98.6%), cough (59.4%) and fatigue (69.6%), which is similar to our study. The rest clinical manifestations resemble those previously reported [16‐20]. It is worth mentioning that higher incidence of severe/critical type of COVID-19 was detected in the elderly group, which might be associated with advanced age and coexistence of basic diseases (hypertension and diabetes). In addition, cough and chest tightness/pain were more commonly emerged in Group 3, which was similar to previous reports [5, 21].

In our study, among all laboratory examinations, CRP increase was the most frequent (59.3%), followed by lymphocytes decrease, then abnormality of neutrophil and WBC counts. It is worth pointing out that few young patients got elevated lymphocytes, which might be ascribed to their strong immune system. Furthermore, nearly half of the elderly patients had mildly elevated WBC, while it was rare in the younger group, such phenomenon was similar to a previously reported study [22]. These results have great value in assessment of COVID-19. In particular, decreased WBC has an important differential diagnosis value when compared with common pneumonia, which is usually accompanied by increased WBC. Compared with Group 1 and 2, there are more abnormal laboratory examination indexes (including CRP increase, abnormal number of lymphocytes, neutrophils and monocytes) in Group 3. It may be related to underlying diseases and immunological dysfunction in aged patients. By summarizing 99 cases, Chen et al. [23] found that COVID-19 was more likely to affect elderly men with comorbidities, and could result in acute respiratory distress syndrome (ARDS). Another study [7] had shown that older patients were correlated with higher severity and mortality of COVID-19, which they found the median age of death was 75 years old for COVID-19, and the median time from symptom onset to death in patients aged 70 and above (11.5 days) was shorter than those below 70 years old (20 days). These results demonstrated that the disease might progress faster in the older patients than in the young.

It is noteworthy that compared with patients who had no basic diseases, patients with basic diseases (Hypertension, Diabetes, hepatitis B and COPD) are more likely to develop into Severe/Critical type. Human pathogenic coronaviruses gain entry into their target cells through angiotensin-converting enzyme 2 (ACE2), which is expressed by epithelial cells of the lung, kidney, vessels and intestine. The increased expression of ACE2 would facilitate infection of COVID-19 [24]. For patients with diabetes or hypertension, treatment with ACE2-increasing drugs increases the risk for severe and fatal COVID-19 infection [25]. A recent study showed that the occurrence of COPD was associated with a nearly four-fold higher risk of developing severe COVID-19 [24]. COPD is defined as chronic infection of large (central) airway, small (peripheral) bronchioles and damage of lung parenchyma. Viral infections caused acute exacerbation of COPD, which can result in impairment of lung function in many patients [26]. A large cohort including 1099 COVID-19 cases indicated that 21 (2.1%) had hepatitis B, more critical type patients had abnormal liver aminotransferase levels than mild type patients [6]. The study suggested that patients with chronic hepatitis were associated with higher mortality after infection of COVID-19 [6]. Therefore, we suggest that basic diseases are crucial risk factors for severe/critical type of COVID-19.

Our study showed COVID-19 had its own representative imaging manifestations. Patients might have one affected lobe or multiple affected lobes. Typical image presentations of COVID-19 include multiple patchy/punctate pGGO or mGGO mainly distributed in subpleural areas, accompanied by halo sign, crazy paving sign, vascular and bronchial dilatation, which were consistent with literature reports [27, 28]. The virus was likely to attack peripheral vascular and bronchus in the early stage of the disease, which caused the increase of the intraductal pressure and resulted in exudation, as reflected by the subpleural pGGO and halo sign. Over time, crazy paving sign was formed due to thickening of the interlobular septum and increased exudation of the alveolus. If the disease continued to progress, the thickened lobular septum limited the absorption of the alveolar exudation, resulting in the alveolar consolidation and mGGO formation. Other less common CT manifestations include reversed halo sign, cavity sign, mild pleural thickening, a little pleural effusion and lymphadenectasis, whose incidence were similar to previous reports [29, 30]. Generally, non-subpleural distribution, single lesion and 1 or 2 affected lobes were more common in Group 1. However, compared with Group 1, multiple lesions, more affected lobes and a wider range of infections were involved in Group 2 and 3. When the ventilation function was seriously impaired, lung CT performance could progress to a “white lung” appearance [31], which was more commonly detected in old patients than young patients. Song et al. [11] found by investigation of 51 patients with COVID-19 that younger patients tended to have more GGOs, while elderly patients tended to have more consolidations and more involved areas of lung. We think it may serve as an alert in the management of patients by identifying these age-related CT signs of COVID-19.

Our study revealed that mild pleural thickening was more commonly seen in elderly patients, most pulmonary lesions existed in multiple lobes, with predominant distribution in posterior and peripheral parts of the lung that were always tightly close to the pleura. Pleural thickening often indicated that the lesion of COVID-19 has invaded the bronchioles and alveolar epithelium of the cortical lung tissue, and the distribution of lesions gradually expanded from the periphery to the central part of the lung. We also found that bronchiectasis was more commonly seen in elderly patients than young patients. In addition, we have noticed that many elderly patients had a history of bronchiectasis. Bronchiectasis may be one of the risk factors for severe/critical type of COVID-19, which needs further study.

It is worth noting that lesions of 18 cases (with 14 in Group 1) were not in the subpleural areas, such imaging features were atypical and might easily be mistaken for common inflammatory GGO. For atypical CT findings, we should pay high attention to timely insulate the suspected cases to avoid possible transmission, meanwhile review the epidemiological histories and suggest RT-PCR test and follow-up CT scans, since most positive cases have a faster progression of CT manifestations in a short time.

Due to the responsible viruses are also coronaviruses, CT manifestations of COVID-19 are similar to those reported with MERS and SARS. CT features such as GGO, consolidation and crazy paving sign were also seen in MERS and SARS. Likewise, pleural effusion and pneumothorax were commonly seen in critical patients with previous Coronavirus pneumonias [32]. In our study, multiple lobes (72.3%) involved by GGO or consolidation (85.7%) distributed in subpleural areas (94.1%) were the main CT manifestations of COVID-19. Moreover, other CT signs such as halo sign, reversed halo sign, crazy paving sign, cavity, vascular dilatation and pleural thickening were commonly seen in our study. To our knowledge, pulmonary cavitation and reversed halo sign have not been mentioned in the literatures about MERS and SARS. Furthermore, unifocal involvement is more prevalent than multifocal involvement on CT of patients with previous Coronavirus pneumonias. As the infectious diseases of MERS or SARS progress, pulmonary infection focus eventually spread to the central area and bilateral upper lobes [33], which is different from COVID-19 in our study.

There are some limitations in this study: 1) We have not evaluated dynamic imaging progress of COVID-19. 2) This study mostly emphasized on the CT imaging features of COVID-19 and the differences among three age groups, yet which CT findings could be used for directing treatment and estimating prognosis of COVID-19 had not been investigated, which will be the concern of the follow-up study.

In summary, our study suggested that elderly age coexisted with basic diseases might serve as important risk factors for heavy/critical type of COVID-19. Compared with young patients, there are more abnormal laboratory examination indexes in elderly patients. CT images revealed that multi-affected lobes, subpleural lesions, crazy paving sign, bronchodilatation and pleural thickening were more commonly seen in the elderly patients than young patients. In some young patients with mild/moderate type, GGO may not appear in the subpleural areas. These atypical CT features need further attention and follow-up is important. Therefore, three age groups of COVID-19 possess their own characteristics. Grasping these characteristics will be helpful for the clinicians to better understand the characteristics of COVID-19 and better guide clinical diagnosis and treatment of this infectious disease.