Review for 10.1186/s12876-021-02035-6 (2021)

Reviewer’s report
Title: 
The effects of preoperative intestinal dysbacteriosis on postoperative
recovery in colorectal cancer surgery: a prospective cohort study
Version: 
0 
Date: 
21 May 2021
Reviewer's report:
The authors describe a single-centre prospective observational study of patients
undergoing operations for colorectal tumours. Microbiological profiles of patient
faecal samples were taken before and after the operation and classified according
to the distribution of organisms in the faecal samples, along with records of post-
operative complications. 
This could be an interesting observational report but requires some, reasonably
substantial, modifications. 
There are detailed notes below, but I believe the main priorities are:
- I would recommend using the STROBE framework to ensure that all the
relevant study details are reported clearly and transparently,
- The inclusion & exclusion criteria should be reported clearly and specifically,
- The statistical methods require attention to ensure analysis is properly justified
and related clearly to the intended investigation.
I would also suggest that this should be reviewed by someone with expertise in
colorectal surgery and/or clinical microbiology. 
There are also issues with the grammar throughout that occasionally impede
understanding.
Introduction
There are some examples of the grammar and structure issues in the first
paragraph. Infections could be some of the most common complications and yet
still not occur in many patients. 
Methods
The cohort definition could be tightened up to better clarify the included
population. For example, it would be preferable to see the specifics of
classification as "colorectal cancer surgery". Did this include specific procedures
(as opposed to those excluded)? Were patients required to have a recorded
cancer diagnosis prior to the surgery, and how was this identified (e.g. ICD
codes, referral to the study from specialist clinics)?
The stated endpoints should be more specific. Additionally, are these intended to
be outcomes or endpoints?
Was the upper age limit an inclusion criteria or is this just how the age of the
included patients was distributed?
The section detailing the dysbiosis score would be better presented as bullet
points or a table, it is quite hard to follow as it is now. Listing grade 0 as item 1
is confusing.
In general, it is unclear whether patient data has come from patient records or
was recorded specifically for the study.
Results
In the section "correlation of pre-operative dysbacteriosis and short term
outcomes", I'm not clear what statistical test the results presented are from.
Please do not report "P=0.00", this value will have been rounded by your
statistical software. 
I'm not sure I understand why other post-operative complications (diarrhoea,
hypoalbuminaemia, etc.) are included in the model of post-operative infectious
complications? If patients were followed for 30 days, these complications could
have occurred after the infectious complication (unless perhaps only those
occurring before infection were included, but this is not stated if so). They may
also be affected by dysbiosis themselves. Either way I am not sure that this is the
most appropriate way to build this model. 
I feel the reporting of the assessment of the stool examination should come
earlier on, as it is important context for the results section. 
A clinical reviewer may be able to advise better, but might the results for patients
with colon and rectal cancer be better assessed separately? The rate of
neoadjuvant therapy for example would be expected to differ by primary cancer
site. 
How were the co-morbidities reported in table 1 selected, and how were patients
classified?
Adding a "totals" column to table 1 would be useful, to report the distribution of
these key characteristics across the whole population. 
What are the ranges reported for the time using antibiotics and length of stay in
table 3?
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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?
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No
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from apparent manipulation?
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