Review for 10.1186/s12876-018-0920-x (2019)

Reviewer ’s report  
 
Title: Retrospective analysis of Clostridium difficile infection in patients with ulcerative colitis 
in a tertiary hospital in China  
 
Version: 3 Date: 28 Sep 2018  
 
Reviewer: Nira Pollock  
 
Reviewer's report:  
 
Xu et al have retrospectively examined risk factors for CDI in patients with UC evalua ted in a 
tertiary hospital setting in China.  The manuscript addresses an important topic and is interesting.  
 
I have the following major comments that I think will improve the manuscript:  
The abstract and methods sections need to be edited to clarify tha t all cases and controls 
presented with the same symptoms, and the only difference separating cases from controls prior 
to analysis was the CDAB result.  In Methods section, p. 5, clarify if all diagnoses of "disease 
flare" were based on the presence of ab dominal pain and diarrhea.  "Diarrhea" also needs to be 
more clearly defined (p. 6).  Was this new onset diarrhea?  Increase over chronic levels?  Seems 
that most but not all had colonoscopy —what determined whether patient had colonoscopy or 
not?  It is no table that only 25/34 cases were treated for CDI (p. 9, line 53).  Why were the others 
not treated?  Importantly, what were the outcomes in the UC patients who were NOT treated for 
CDI despite their CDAB+ result?  Given the controversy in the field about w ho needs to be 
treated, and given the recommendation to screen all UC patients with flare for CDI (guidelines 
and p. 11, line 28), this outcomes data would be very useful.  Did those who weren't treated "for 
CDI" get treatment for UC flare that would have included treatment active against C. difficile 
(e.g. metronidazole)?  (It would be helpful to know what the default treatment for UC flare is in 
this hospital.)  Similarly, how did the CDAB+ patients who received increased doses of steroids 
(p. 10, line 6)  do (and were those patients also treated for CDI, or not?)?  
In order to understand the CMV infection data/conclusions in the paper, more detail needs to be 
provided about CMV results in each study cohort.  What % of patients with CMV infection were 
defin ed by positive CMV IgM only?  Diagnosis of CMV colitis is optimally made by identifying 
CMV inclusions/positive staining for CMV on histopathology of a tissue biopsy; culture of the 
biopsy for CMV can also be performed.  It isn't clear from the methods sec tion (p. 6) that biopsy 
was performed —rather, diagnosis depended on CMV IgM, and CMV DNA/pp65 antigen 
detection in blood (sample type is not actually mentioned, and should be —I am assuming blood).  
Blood PCR testing can sometimes be negative in patients wi th active CMV colitis, so is not 
considered the mainstay of diagnosis. CMV pp65 antigenemia would be subject to the same 
limitations.  CMV culture of stool can be positive even in asymptomatic viral shedding, rather 
than disease (and even biopsies can pote ntially be contaminated by stool).   CMV IgM isn't a 
typical way to diagnose disease in immunocompromised patients, in particular; also, after acute 
CMV, CMV IgM can persist for months.  Without baseline serostatus, I am not sure how to 
interpret any posit ive IgM results in these study patients.  
The analysis of median steroid dose is confusing (p. 8).   The median dose equivalent of 0 in the 
controls implies that the median was calculated in the entire control cohort, rather than just the 
subset on steroid s.  Please clarify.  
Why was the followup window so long (p. 9, line 48)?  This means that it was not equivalent for 
all patients, and it also confuses any ability to relate outcomes to the CDI diagnosis.  
 The authors should present a hypothesis as to wh y antibiotic exposure within 3 months of 
presentation, but not within 1 month of presentation, was associated with CDI, as this is 
counterintuitive.  
In the limitations section, the authors might wish to acknowledge that it is possible that CDAB 
toxin presence was not reliably diagnostic of CDI in the UC patients, given that a recent paper 
(Pollock et al, Clinical Infectious Diseases 2018) found that to xin concentration distributions in 
CDI patients and asymptomatic carriers fully overlapped.  This doesn't detract from the 
conclusions of the study but could be acknowledged as a limitation.  Since the results from the 
CDAB test were reported in RFV, it wo uld be interesting to know how "positive" the positive 
samples were in the case cohort (and particularly in the two patients with pseudomembranes, p. 
9). 
 
Minor:  
--p. 4, line 34 and following:  edit to clarify "need for treatment of more active for IBD"  
--p. 4, line 53 -56:  does "history of colitis" refer to IBD colitis or CDI colitis or ?  
--I'm not sure that the refs cited for the modified Mayo score (p. 6) are correct.  
--p. 6, line 23:  how was hematochezia considered to support or refute a CDI diagnosis  in these 
UC patients?  
--p. 6, line 48:  how did they know that "medication for CDI" (e.g. metronidazole) was not part 
of the UC treatment?  
--p. 7, line 56 -59:  are the % given related to the CDAB+ group only, or the whole study group?  
--p. 12, line 31:  w hat does "maintenance of immunomodulators" mean here?  
--p. 13, line 12:  the "trend to recurrence" seems like an overstatement, as only 2 patients seem to 
have recurred.  
--p. 13, line 42:  what kind of bias, specifically?  
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
No 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the authors.  
 
Yes 
 
Are the conclusions drawn adequately supported  by the data shown?  
If not, please explain in your comments to the authors.  
 
Unable to assess  
 
Are you able to assess any statistics in the manuscript or would you recommend an  
additional statistical review?  
If an additional statistical review is recommended , please specify what aspects require further  
assessment in your comments to the editors.  
 
I recommend additional statistical review  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Needs some language corrections before  being published  
 
Declaration of competing interests  
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1. Have you in the past five years received reimbursements, fees, funding, or salary from an  
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3. Do you hold or are you currently applying for any patents relating to the content of the  
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