Introduction

Coronavirus disease 2019 (COVID-19) is an infectious disease caused by the most recently discovered RNA virus named coronavirus, formerly referred to as severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) [1]. It causes tract infections within the human and animal bodies present with fever, cough, cold, and sometimes patients may die due to acute respiratory distress syndrome or pneumonia [2]. Coronaviruses are a beta coronavirus that constitutes the subfamily Orthocoronavirinae, and family Coronaviridae. The name “coronavirus” is derived from Latin word corona, meaning as crown or wreath. Coronaviruses were first discovered in the 1930s in North Dakota with an acute respiratory tract infection of domesticated chickens [1]. Among seven coronavirus species that are identified to infect human beings and cause disease, HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1 are generally mild, often cause normal cold side effects. Other three human coronaviruses, middle east respiratory syndrome-related coronavirus (MERS-CoV), severe acute respiratory syndrome coronavirus (SARS-CoV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) produce potentially severe symptoms, which have been identified in 2012, 2002 and 2019 respectively [3, 4].

The first case of COVID-19 disease was identified on December 8, 2019, in Wuhan, the Hubei province of China by the Chinese Center for Disease and Prevention from the throat swab of a patient [5]. Since COVID-19 disease emergence first in China, it’s rapidly become a worldwide threat and it’s declared as a pandemic by World Health Organization (WHO). From that time, this disease has spread to 216 countries and territories around the world, with 20,995,433 confirmed cases and 760,774 deaths (World Health Organization statistics as on August 15, 2020) [6]. The case fatality rate is high for COVID-19 infection. Globally the death rate was 3.6% [6]. The highest confirmed number of cases was reported in the United States of America with 5,150,407 confirmed cases with 164,826 deaths. From the European region, the majority of confirmed cases/death was accounted from the Russian Federation, Spain, UK, Italy (912,823/15,498, 337,334/28 605, 313,802/46 706, 252,235/35 231) respectively. In the African region, the highest confirmed cases/death was found in South Africa (572,865/11 270) and in the Eastern Mediterranean region highest cases/death was found in Iran (336,324/19 162). From the South-East Asia region, India accounted for the highest number of cases/death (2,461,190/64 553). In Bangladesh, the confirmed number of cases was 269,115 with 3 557 deaths up to August 15, 2020 [6].

Patients with COVID-19 present primarily with various symptoms like fever, cough, dyspnea, myalgia, and fatigue [7, 8]. Although most of the COVID-19 infected patients are thought to be recovered after few days, male patients, older patients (age greater than 60 years) and patients with various chronic diseases may have fetal outcomes [9].

Several factors are responsible for the severity and mortality of COVID-19 disease. From different studies, it had been found that patients with comorbidities such as hypertension, diabetes mellitus, acute respiratory distress syndrome (ARDS), cardiovascular disease, cancer, COPD, asthma, renal disease, kidney disease, liver disease, hepatic disease, pneumonia, obesity, and also for the history of smoking were responsible for the development of the disease or death [10,11,12,13,14]. The mortality rate of COVID-19 patients were varied among the intensive care unit (ICU) and non-ICU patients and also for severe and non-severe patients. From different studies, it had been found that the mortality rate was higher among ICU admitted patients and severe patients compared to non-ICU and non-severe patients [15,16,17].

Low and middle-income countries like Bangladesh, COVID-19 disease is sort of a threat to health and economic sectors. Proper social distancing is not possible for a large number of populations, which is essential to prevent this disease because of having no proper treatment or medicine to treat coronavirus infected patients and vaccine to prevent it. Numerous requiring ICU care and mechanical ventilator, which is difficult to arrange for many develo** countries [18]. Proper steps should be taken to prevent this disease and reduce the mortality rate. Several studies had reported the risk factors associated with death among COVID-19 patients [10,11,12,13,14]. In this study, we aimed to review the prevalence of mortality and the risk factors associated with mortality among coronavirus infected patients in the hospital and to summarize the available findings in a meta-analysis.

Methods

Search Strategy

A systematic search had been performed using the online databases of PubMed, Science Direct and Google Scholar for relevant publications from January 1, 2020, to August 11, 2020. Advanced search strategy with the following combined text heading as (“coronavirus” OR “COVID-19” OR “novel coronavirus” OR “SARS-CoV-2” OR “2019-nCoV” OR “Severe Acute Respiratory Syndrome related coronavirus”) AND (“mortality” OR “death” OR “fatal outcome”) AND (“risk factors”) had been used to find out the potential paper. An initial search had been carried out followed by an analysis of the text words contained in Title/Abstract. A literature search had been done by two independent reviewers (FMN and MMI).

Study Eligibility Criteria

We included the articles assessing the association between age, gender, comorbidities and mortality risk factors from COVID-19 infection as the major outcomes of interest. Articles that reported SARS-CoV-2 infected patients confirmed by real time reverse transcriptase polymerase chain reaction (RT-PCR) were included. Studies that didn’t report the prevalence of mortality among COVID-19 patients were excluded. For this analysis purpose, studies with only cohort study design were used. Randomized controlled trials, cross-sectional study, case–control study and case report study design were excluded. Editorials, systematic review articles, letters to editors and short communication were also excluded for this analysis. Studies that included only pediatric patients, pregnant women, surgery patients and patient co-infection with other diseases were excluded due to heterogeneous results found among those groups for coronavirus disease. Articles were written in English language and only human based studies were included. Only published and peer reviewed articles were included in the analysis. Unpublished articles were excluded due to data uncertainty. All the identified articles were investigated by hand and not recognized by electronic inquiry. Duplicate articles were found out and extracted at last. Titles and abstracts were searched by two independent researchers. Controversial matters were resolved after discussion.

Data Extraction Process and study Quality Assessment

Two reviewers independently screened full articles after an initial search by title and abstract for inclusion and exclusion criteria. The extracted data included: confirmation of SARS-CoV-2 infected patients, study design, time and place of data collections, author name, year of publication, country, the total number of reported cases, the total number of fatality cases, gender, age, comorbidities (e. g., hypertension, diabetes, cardiovascular disease, etc.). The results of this analysis were presented based on the PRISMA checklist [19]. Newcastle–Ottawa technique was used for the quality assessment of the included cohort studies [20]. Three major components were utilized to assess the quality of the included studies such as selection procedure of the study patients, coordination of efficient confounding variables and assessment of the outcome and the article’s point with more than 5 were considered as high-quality publications among maximum 9 points [21].

Statistical Analysis

Data analysis was carried out using STATA version 16 and Microsoft Excel. The pooled prevalence rate (PR), risk ratio (RR) and 95% confidence interval (CI) for both of those were calculated using random effects model to pool weighted effect size as well as every individual study. PR was used to calculate the prevalence of mortality among hospitalized patients with COVID-19 and RR was used to calculate the risk of mortality. Random effects model was used in this analysis as there was substantial heterogeneity among the study results. In meta-analysis a random effects model assumes that the effect size of all studies is not uniform and may follow a distribution [22, 23]. For examining the between-study heterogeneity, chi-square test statistic (Q), and \({I}^{2}\) and \({\tau }^{2}\) test were used in this analysis [23, 24]. Forest plot was used as a graphical representation of heterogeneity among the included studies. Substantive heterogeneity among the included studies result was identified by subgroup analysis based on continent. A sensitivity analysis was conducted to find the effect of a single study on the overall study result. Publication bias was detected by funnel plot [25].

Results

Search Results and Study Characteristics

A total of 2147 articles were identified from three databases PubMed, Science Direct and Google Scholar. After screening those articles by title and abstract, 340 articles were identified. Of those, 144 articles were selected for full text assessment. Among those, 58 articles with 122,191 participants reporting the mortality rate and risk factors of mortality among hospitalized patients with confirmed COVID-19 infection as a primary outcome were included. Rest of the 86 articles were excluded due to lack of proper information, study design and duplication. Finally, 58 cohort studies were included in this meta-analysis (Fig. 1). The characteristics of all the included studies were described in (Table 1).

Fig. 1
figure 1

PRISMA flowchart for search strategy and the process of selecting articles

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Table 1 Characteristics table for included studies
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Among the included studies, 26 studies were conducted in China [10,11,12,13, 26,27,28,29,84]. Acute respiratory distress syndrome is found at the early stages of COVID-19 infected patients and cytokine can lead to acute respiratory distress syndrome, which is one of the main reasons for fatality among the patients [9].

Findings from this analysis would help the policymakers of health care sectors to develop different strategies, management and stratified the patients according to risk for giving proper treatments and nursing with limited resources.

Limitations

This meta-analysis had some limitations. Articles only published in the English language were included in this analysis. The sample size of some included studies was very small which might not recognize uncommon factors. Biasness and high heterogeneity among the included studies was also found. Some risk factors could not be included due to data insufficiency. Evidence of publication bias was also found in the data. However, included studies showed good quality assessments.

Conclusion

This meta-analysis result revealed that the mortality rate among hospitalized COVID-19 patients was high and male gender, older aged patients, patients presented with comorbidities such as hypertension, diabetes, cardiovascular disease etc were highly associated with the risk of death among them. Those findings would help the health care providers or physicians to notice the risk of high mortality among the COVID-19 infected patients and take proper management strategies in health care sectors to reduce this high mortality rate and also combat this COVID-19 pandemic to save human lives.