Review for 10.1186/s12876-022-02132-0 (2022)

Reviewer’s report
Title: 
Are Gastrointestinal Symptoms Associated with Higher Risk of Mortality
in COVID-19 Patients? A Systematic Review and Meta-Analysis
Version: 
1 
Date: 
23 Mar 2021
Reviewer's report:
PEER REVIEWER ASSESSMENTS: 
OBJECTIVE - Full research articles: is there a clear objective that addresses a
testable research question(s) (brief or other article types: is there a clear
objective)?
Yes - there is a clear objective
DESIGN - Is the current approach (including controls and analysis protocols)
appropriate for the objective?
Yes - the approach is appropriate
EXECUTION - Are the experiments and analyses performed with technical rigor
to allow confidence in the results?
Yes - experiments and analyses were performed appropriately
STATISTICS - Is the use of statistics in the manuscript appropriate?
Yes - appropriate statistical analyses have been used in the study
INTERPRETATION - Is the current interpretation/discussion of the results
reasonable and not overstated?
No - there are minor issues
OVERALL MANUSCRIPT POTENTIAL - Is the current version of this work
technically sound? If not, can revisions be made to make the work technically
sound?
Probably - with minor revisions
PEER REVIEWER COMMENTS: 
GENERAL COMMENTS: 
I have reviewed this manuscript. I am unsure whether there were any previous
reviewers comments, but comments were addressed to the Editor. The study has
a clear objective and a protocol has been published. There are a few comments
for the authors, mainly about some of the conclusions made that could be more
objective.
REQUESTED REVISIONS: 
In Line 158: What proportion of the study population included does the four
studies from the USA/Europe represent? Please include that as it is important for
this to clarify the point made.
Line 195: Why are these results considered odd? 
Page 7, Lines 198-Page 8 line 204 "Thus the heterogeneity in the included
studies might be partially related to the patient selection bias in USA and Europe
hospitals. On the other hand, follow-up time in the 4 studies was relatively short
because of the urgent need for..." The conclusions drawn here seem biased and
subjective. The info preceding this indicates that persons with GI symptoms
were prioritised for treatment in hospital which is a desirable and consistent
practice across the four studies. How can this be described as biased? The fact
that the outcomes do not match what the authors are looking for, does that make
it biased? Authors need to look for a more objective perspective on the
difference in the results obtained for studies in USA/Europe vs China. A
reasonable conclusion can be focused on any difference in clinical practice or
protocols between different settings and the timeliness of interventions that have
lead to different outcomes in each setting. 
Pg 8, line 225: It is unclear what this sentence means 'The pooled OR estimate
tended to favor the presence of GI symptoms...'. Please rephrase.
Pg 11, Line 295: Once again, I suggest the authors be more objective with their
conclusion. The USA studies were generally larger sample size and the OR for
that subgroup indicated GI symptoms were more protective. The Chinese studies
OR was 1.01 and was not significant. So the general result of this study is that GI
symptoms are not associated with worse prognosis. Based on statistical
principles, the larger sample size in the sub-group of USA/Europe studies
indicated a stronger support for the outcome, which confirms the overall result.
ADDITIONAL REQUESTS/SUGGESTIONS: 
A few grammatical errors.
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Is the study design appropriate to answer the research question (including the use
of appropriate controls), and are the conclusions supported by the evidence
presented?
No
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Yes
Is the use of statistics and treatment of uncertainties appropriate?
Yes
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No
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes