Journal of Global Infectious Diseases

: 2021  |  Volume : 13  |  Issue : 1  |  Page : 13--19

Clinical determinants of severe COVID-19 disease – A systematic review and meta-analysis

Ankit Kumar Sahu1, Roshan Mathew1, Praveen Aggarwal1, Jamshed Nayer1, Sanjeev Bhoi1, Swayamjeet Satapathy2, Meera Ekka1,  
1 Department of Emergency Medicine, All India Institute of Medical Sciences, New Delhi, India
2 Department of Nuclear Medicine, Post Graduate Institute of Medical Education and Research, Chandigarh, India

Correspondence Address:
Dr. Jamshed Nayer
Department of Emergency Medicine, All India Institute of Medical Sciences, New Delhi


Background: A systematic review and meta-analysis of available studies was performed to investigate the clinical characteristics that can predict COVID-19 disease severity. Materials and Methods: Databases including PubMed, Embase, and Web of Science were searched from December 31, 2019, to May 24, 2020. Random-effects meta-analysis was used for summarizing the Pooled odds ratio (pOR) of individual clinical characteristics to describe their association with severe COVID-19 disease. Results: A total of 3895 articles were identified, and finally, 22 studies comprising 4380 patients were included. Severe disease was more common in males than females (pOR: 1.36, 95% confidence interval [CI]: 1.08–1.70). Clinical features that were associated with significantly higher odds of severe disease were abdominal pain (pOR: 6.58, 95% CI: 1.56–27.67), breathlessness (pOR: 3.94, 95% CI: 2.55–6.07), and hemoptysis (pOR: 3.35, 95% CI: 1.05–10.74). pOR was highest for chronic obstructive pulmonary disease (pOR: 2.92, 95% CI: 1.70–5.02), followed by obesity (pOR: 2.84, 95% CI: 1.19–6.77), malignancy (pOR: 2.38, 95% CI: 1.25–4.52), diabetes (pOR: 2.29, 95% CI: 1.56–3.39), hypertension (pOR: 1.72, 95% CI: 1.23–2.42), cardiovascular disease (pOR: 1.61, 95% CI: 1.31–1.98) and chronic kidney disease (pOR: 1.46, 95% CI: 1.06–2.02), for predicting severe COVID-19. Conclusion: Our analysis describes the association of specific symptoms and comorbidities with severe COVID-19 disease. Knowledge of these clinical determinants will assist the clinicians in the risk-stratification of these patients for better triage and clinical management.

How to cite this article:
Sahu AK, Mathew R, Aggarwal P, Nayer J, Bhoi S, Satapathy S, Ekka M. Clinical determinants of severe COVID-19 disease – A systematic review and meta-analysis.J Global Infect Dis 2021;13:13-19

How to cite this URL:
Sahu AK, Mathew R, Aggarwal P, Nayer J, Bhoi S, Satapathy S, Ekka M. Clinical determinants of severe COVID-19 disease – A systematic review and meta-analysis. J Global Infect Dis [serial online] 2021 [cited 2021 Apr 11 ];13:13-19
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Full Text


The novel coronavirus, named as severe acute respiratory syndrome coronavirus 2, was identified in Wuhan, China, in December 2019. The disease caused by the virus, COVID-19, has created havoc all over the world and has been declared pandemic by the World Health Organization (WHO). As of March 21, 2020, 11,183 patients have succumbed to this disease and with the rapid spread of the disease, these numbers might run into millions.[1]

The clinical spectrum of COVID-19 disease is wide, ranging from nonsevere (asymptomatic infection and mild respiratory tract infection) to severe disease (severe pneumonia and critical illness, including multiorgan dysfunction).[2] In a case series of 44,672 confirmed COVID-19 patients, 14% had severe, and 5% had critical disease.[2] However, most of the patients present with fever, dry cough, myalgia and have a favorable prognosis.[2] Older patients and those with comorbidities progress to severe disease and have worse outcomes.[3]

With overwhelmed health-care systems and no proven treatment, it is important to identify the patients who could have a high likelihood of progression to severe disease. This will help the concerned physicians to allocate the resources judiciously. The goal of this investigation was to identify the clinical determinants which are associated with severe COVID-19 disease.

 Materials and Methods

Data sources and searches

This systematic review was performed according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA). Databases including PubMed, Embase, and Web of Science were searched from December 31, 2019, to May 24, 2020. There were no restrictions in terms of country, publication language or publication date. Reference lists of all relevant articles and “related citation” search tool of PubMed were checked for any additional publications. The detailed search criteria used are available in Supplement.

Selection criteria

Study selection was performed by two independent investigators (A. S. and P. A.). We included studies that focused on individual symptoms and comorbidities of laboratory-confirmed COVID-19 patients and reported the data according to disease severity or ICU admission. Case reports, duplicate publications, reviews, editorials, letters, and family-based studies, studies with insufficient data on symptoms/comorbidities on admission in either severe or non-severe disease groups, and studies reporting exclusively on pediatric (<18 years age) or pregnant populations were excluded. Discrepancies between the reviewers were resolved in the presence of a third reviewer (J. N.).

Data abstraction and quality assessment

Data collected included: study characteristics – authors, publication date, study design, country, sample size; patient's characteristics – median age with interquartile range, sex (% men); criteria for severe disease; total number of severe and non-severe patients; and clinical characteristics (clinical features and comorbidities) at admission – overall prevalence and prevalence among severe and non-severe patients. One reviewer extracted the data (A. S.) and second reviewer (S. S) verified the data independently. The methodological quality of the study was assessed with the Appraisal tool for Cross-Sectional Studies (AXIS) tool.[4] Two authors (S. S, A. S.) performed the quality assessment separately, and disagreements were resolved by consensus in the presence of a third reviewer (P. A.). In the AXIS tool, for every correct answer, score of one was assigned to each of the twenty questions.

Quantitative data synthesis

Patient numbers were extracted across all the included studies for each group (severe and non-severe) according to the individual symptoms and comorbidities. The odds ratio (OR, 95% confidence intervals [CIs]) of individual clinical characteristics was used to describe their association with severe COVID-19 disease. These ORs were further pooled using random-effects meta-analysis. To assess the heterogeneity among studies, inconsistency statistics (I2) were calculated. I2 >50% was considered as significant heterogeneity. Publication bias was visually analyzed from Funnel plots and Egger's regression was also performed. P value for Egger's regression coefficient < 0.05 was considered as significant publication bias. All data were collected in Microsoft Excel Spreadsheet (MS Office – 2018). Random-effects analysis, generation of forest plot, assessment of heterogeneity, and publication bias were performed with the METAN platform for STATA (version-14.2); StataCorp, College Station, TX.

As the study design was a systematic review and meta-analysis, Institute Ethics Committee approval was not sought.


Search results and study characteristics

The literature search flow diagram is summarized in PRISMA format [Figure 1]. Using our search criteria (available in supplement), we identified 3895 studies, of which 3645 were from PubMed, 50 were from EMBASE, and 200 were from Web of Science. A total of 209 records were screened after the removal of duplicates. A total of 87 full-text articles were assessed for eligibility and 65 articles were excluded due to various reasons, as shown in [Figure 1]. Finally, 22 studies were included in this meta-analysis.{Figure 1}

Characteristics of included studies

A total of 22 studies, consisting of 4380 patients, were selected for this meta-analysis [Table 1]. Studies were published recently between January 24, 2020 and May 24, 2020. Individual study population size ranged between 12 and 1494 patients. Fifty-six percent of the study population were males. Median age of the patients in severe disease cohort varied from 45.2 to 67 years, whereas median age in non-severe disease cohort varied from 37 to 68.5 years. Individual symptoms studied were cough,[5],[6],[7],[9],[10],[12],[16],[18],[19],[20] expectoration,[5],[6],[7],[9],[10],[14],[18],[19],[21] fever,[5],[6],[9],[10],[11],[13],[14],[15],[16],[17],18],19],[20],[21] breathlessness,[5],[6],[9],[10],[11],[13],[14],[15],[16],[17],18],19],[20],[21] hemoptysis,[5],[6] sore throat,[5],[7],[9],[10],[15],[16],[18],[21] fatigue,[5],[6],[9],[10],[11],[13],[14],[16],[17],[18] myalgia,[6],[7],[9],[10],[12],[16],[18],[19],[21] headache,[5],[6],[7],[8],[9],[10,[12],[16],[18],[21] nausea/vomiting,[5],[9],[11],[12],[16],[18],[21] diarrhea,[5],[7],[9],[11],[12],[15],[16],17],[18],[21] abdominal pain,[9],[11] anorexia,[9],[11] and anosmia.[16],[18] The various comorbidities studied were chronic obstructive pulmonary disease (COPD)[5],[6],[7],[9],[11],[12],[16],[17],[18,[19],[21],[22],[23],[24],[25],[26] diabetes[5],[6],[7],[9],[11],[12],[13],[14],[16],[17],[18],[19],[21],[22],[23],[24],[25],[26] obesity,[16],[18],[22] hypertension,[5],[6],[7],[9],[11],[12],[13],[14],[16],[17],[18],[19],[21],[22],[23],[25],[26] cardiovascular disease (CVD), [5],6],[7],[9],[11],[12],[13],[14],[16],[17],[18],[19],[21],[22],[24],[25] cerebrovascular accidents,[5],[9],[11],[16],[18],[19],[21],[24] chronic kidney disease (CKD),[5],[9],[11],[12],[16],[18],[21],[24],[25],[26] chronic liver disease,[6],[9],[11],[19],[21],[24] malignancy,[5],[6],[9],[16],[17],[19],[21],[23],[26] and immunocompromised state.[5],[18],[24] Majority of the studies (13) were from China,[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[22],[23],[26] however, three studies were from the United States,[16],[18],[4] two from Italy[17],[21] and one each from Singapore,[15] Norway,[20] South Korea[19] and Israel.[25] Each study was retrospective observational in design. The number of clinical characteristics including comorbidities reported in each study, varied from 3 in one study[20] to 21 in another study.[5] Patients with severe disease were older compared to those with non-severe disease (59.8 years vs. 50.8 years, P = 0.008). According to the WHO-China joint mission,[2] severe disease was defined as tachypnea (≥30 breaths/min) or oxygen saturation ≤ 93% at rest, or ratio of arterial oxygen saturation and fraction of inspired oxygen < 300 mmHg, and critical disease was defined as respiratory failure requiring mechanical ventilation, shock, or other organ failure that requires intensive care. Severe/critical disease were considered “Severe” in most of the studies.[5],[7],[8],[10],[12],[16],[23] Intensive care unit (ICU) admission was considered as “Severe/critical disease” in six studies.[18],[19],[20],[21],[24],[25] Results of quality assessment of the included studies are summarized as AXIS scores in [Table 1]. Overall quality of studies was good, with thirteen out of twenty-two studies having scores above average (score ≥ 15).{Table 1}

Quantitative data synthesis results

ORs of severe disease were pooled for each of the individual symptoms and comorbidities. Forest plots of pOR and funnel plots for each of the clinical determinants are depicted in [Supplementary Figure S1], [Supplementary Figure S2], [Supplementary Figure S3], [Supplementary Figure S4], [Supplementary Figure S5], [Supplementary Figure S6], [Supplementary Figure S7], [Supplementary Figure S8], [Supplementary Figure S9], [Supplementary Figure S10], [Supplementary Figure S11], [Supplementary Figure S12], [Supplementary Figure S13], [Supplementary Figure S14], [Supplementary Figure S15], [Supplementary Figure S16], [Supplementary Figure S17], [Supplementary Figure S18], [Supplementary Figure S19], [Supplementary Figure S20], [Supplementary Figure S21], [Supplementary Figure S22], [Supplementary Figure S23],[Supplementary Figure S24], [Supplementary Figure S25], [Supplementary Figure S26], [Supplementary Figure S27], [Supplementary Figure S28], [Supplementary Figure S29], [Supplementary Figure S30], [Supplementary Figure S31], [Supplementary Figure S32], [Supplementary Figure S33], [Supplementary Figure S34], [Supplementary Figure S35], [Supplementary Figure S36], [Supplementary Figure S37], [Supplementary Figure S38], [Supplementary Figure S39], [Supplementary Figure S40], [Supplementary Figure S41], [Supplementary Figure S42], [Supplementary Figure S43], [Supplementary Figure S44], [Supplementary Figure S45], [Supplementary Figure S46], [Supplementary Figure S47], [Supplementary Figure S48], [Supplementary Figure S49], [Supplementary Figure S50], [Table 2] and [Figure 2] summarizes the pOR for each clinical determinant (clinical feature at admission and comorbidities). Severe disease was more common in males than females (pOR: 1.36, 95% CI: 1.08–1.70). Clinical features associated with significantly higher odds of disease severity were abdominal pain (pOR: 6.58, 95% CI: 1.56–27.67) and breathlessness (pOR: 3.94, 95% CI: 2.55–6.07). Fever (pOR: 1.48, 95% CI: 1.19–1.85) and hemoptysis (pOR: 3.35, 95% CI: 1.05–10.74) were also associated with severe disease, although their lower confidence levels were approaching near one. Patients with comorbidities were also at higher odds of presenting with severe COVID-19 disease. pOR was highest for COPD (pOR: 2.92, 95% CI: 1.70–5.02), followed by obesity (pOR: 2.84, 95% CI: 1.19–6.77), malignancy (pOR: 2.38, 95% CI: 1.25–4.52), diabetes (pOR: 2.29, 95% CI: 1.56–3.39), hypertension (pOR: 1.72, 95% CI: 1.23–2.42), CVD (pOR: 1.61, 95% CI: 1.31–1.98) and CKD (pOR: 1.46, 95% CI: 1.06–2.02). With the exception of the studies considered for breathlessness, nausea/vomiting, anorexia, and diabetes, none of the studies included in the meta-analysis for comorbidities had statistical heterogeneity (I2 < 50%). Funnel plot analyses [Supplementary Figures: S1-S50] and Egger's regression [Table 2] demonstrated the evidence of publication bias in the meta-analysis of studies focussing on fever, COPD and CVD.[INLINE:1][INLINE:2][INLINE:3][INLINE:4][INLINE:5][INLINE:6][INLINE:7][INLINE:8][INLINE:9][INLINE:10][INLINE:11][INLINE:12][INLINE:13][INLINE:14][INLINE:15][INLINE:16][INLINE:17][INLINE:18][INLINE:19][INLINE:20][INLINE:21][INLINE:22][INLINE:23][INLINE:24][INLINE:25][INLINE:26][INLINE:27][INLINE:28][INLINE:29][INLINE:30][INLINE:31][INLINE:32][INLINE:33][INLINE:34][INLINE:35][INLINE:36][INLINE:37][INLINE:38][INLINE:39][INLINE:40][INLINE:41][INLINE:42][INLINE:43][INLINE:44][INLINE:45][INLINE:46][INLINE:47][INLINE:48][INLINE:49][INLINE:50]{Table 2}{Figure 2}


COVID-19 is a rapidly progressing pandemic affecting millions of people worldwide. With the surge of cases, it is expected to overwhelm health-care systems, thereby making it important for physicians to identify clinical characteristics that could point toward progression-to-severe illness. In our meta-analysis of 4380 patients, we found that patients presenting with complaints of breathlessness, hemoptysis and/or abdominal pain, and comorbidities had significantly higher odds of having severe disease.

Multiple studies have shown that patients with breathlessness on arrival had a higher likelihood development of acute respiratory distress syndrome and ICU requirements.[7],[14],[9] In studies conducted by Guan et al. and Huang et al., the incidence of hemoptysis was higher among patients with severe disease as compared to that of non-severe disease, although its proportion was lower in both the study groups.[5],[6] In a study by Zhang et al., few COVID-19 patients presented with atypical abdominal pain and were initially admitted to the surgical ward but subsequently required ICU. These patients were presumed to infect others during their hospital stay, and the newly infected patients also had abdominal pain at presentation. Hence, some authors have suggested the gastrointestinal tract as an alternative route for viral transmission.[27] Hence, it is necessary to not miss abdominal pain as a rare but important predictor of severe disease. Therefore, any patient presenting with SARI with suspicion of COVID-19 and complaints of breathlessness, hemoptysis and/or abdominal pain should be admitted and evaluated further before deciding further course of treatment. These symptoms, along with fever and cough, might act as warning signs of severe disease.

In most of the included studies, the patients in the severe group had a higher median age when compared to the non-severe group, which was consistent with previous reports.[14],[23] Our meta-analysis showed that patients with COPD had the highest risk of the development of severe disease, followed by obesity, malignancy, diabetes, hypertension, CVD, and CKD. A previous meta-analysis of eight studies had shown CVD, respiratory illness, and hypertension as significant predictors of severe disease.[28] The study differs in terms of the inclusion of a greater number of studies and comorbidities. A weaker immune system might explain the higher likelihood of the development of severe disease among older patients with comorbidities.

There are certain limitations of this meta-analysis. The studies included are retrospective in nature with considerable heterogeneity. Further, 13 out of 22 of the studies are from a single country. The criteria of severe disease were also not similar across all the included studies, thereby limiting the strength of our observations. We have also not included the studies exclusively reporting predictors of mortality in COVID-19 patients. Finally, it is possible that newer studies might have been published between the completion of this literature review and its publication.


Our analysis describes the presence of a significant association of the severe disease with the male gender and specific presenting symptoms such as breathlessness, abdominal pain, hemoptysis, fever, and cough. The presence of comorbidities, namely, COPD, CKD, diabetes, CVD and hypertension were also significant risk factors for severe disease, which is in line with previous studies. Knowledge of these clinical determinants will assist the clinicians in the risk-stratification of the patients for better triage and clinical management.

What is already known on the subject

Patients with COVID-19 presents with a wide spectrum of clinical manifestations, i.e., asymptomatic, mild upper respiratory tract symptoms, severe disease, and critical diseaseIt is difficult to predict the disease progression early in the course of illnessMultiple laboratory parameters, comorbid illness, and advanced age have been shown to predict the disease prognosis.

Study's main messages

This updated meta-analysis consisted of 22 studies comprising 4380 patientsSevere disease was more common in males than femalesClinical features that were associated with significantly higher odds of severe disease were abdominal pain, breathlessness, and hemoptysispOR was highest for chronic obstructive pulmonary disease, followed by obesity, malignancy, diabetes, hypertension, CVD , and CKD, for predicting severe COVID-19Knowledge of these clinical determinants will help the clinician to triage and manage the patients carefully, and appropriately allocate the resources in this resource-constraining pandemic.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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