Review for 10.1186/s12876-015-0393-0 (2015)

Reviewer’s report  
 
Title: Perceived food intolerance and irritable bowel syndrome in a population 3 years after a 
giardiasis -outbreak: a historical cohort study  
 
Version: 0 Date: 29 Sep 2015  
 
Reviewer: Askin Erdogan  
 
Reviewer's report:  
 
Dear Editor,  
I have  revised the paper "Perceived food intolerance and irritable bowel syndrome in a 
population 3 years after a giardia outbreak: a historical cohort study". The study aims to 
investigate the prevalence of food intolerance in groups 1) those exposed to giardia  lamblia 3, 
and 2) control group as well as relation of food intolerance to IBS and association with 
FODMAP. However I have some concerns regarding the paper as listed below.  
Abstract:  
1. Results section: The paragraph starts with "The response rate…" This s tatement misleads the 
readers as if there is a treatment and the response rate is given. However this indicates the 
subjects who have responded the questionnaire sent by mail. In "Variables" under methods 
section subjects who completed forms were referred as  "respondents" which is more 
appropriate than "responders". This statement needs to be corrected throughout paper.  
Methods:  
1. Same comment as above.  
2. One of the main critics regarding paper is characteristics of control group. Authors state that 
control co hort were established by sampling 2 people of the same age and gender for each 
exposed patient from entire population of Bergen. Although they state that study population 
has been published previously authors need to be clear and give details of the study 
population. Also it is not known:  
a. Whether control subjects did or did not have either history of giardia or bowel infection in 
the past or present, or IBS or any GI symptoms at the time of selection or in the last 3 years.  
b. Whether exposed subjects had IBS or food intolerance in the previous years before exposure 
or did they have any more GI infections after giardia exposure.  
3. Variables: Question 1; the authors state that the answers were further dichotomized in 3 
ways. However subgrouping subjects with "none  abdominal symptoms" in subgroups given 
as follows;  (no: 2) none or light vs. moderate or severe symptoms or (no:3) none, light or 
moderate vs. severe does not look appropriate. Adding subjects with no symptoms in groups 
where subjects report symptoms may  not be appropriate.  
4. Question 2: Authors state that for respondents who answered "no symptoms" or had a 
missing answer to Question 1 but still gave an affirmative response about specific types of 
food causing symptoms, the response was reclassified as "lig ht". It may be more appropriate 
to classify these subjects in "yes" answer rather than including in further subgroup of "light".  
Results:  
1. Authors do not provide some results and state that "data not shown". Instead these data may 
be provided as supplementa ry material.  
Discussion  
 I agree with the limitations of the study. The main weakness of the paper is that the 
background of subjects exposed to giardia or controls is not clear.  
 
Yours sincerely  
Are the methods appropriate and well described?  
If not, plea se 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.  
 
Yes 
 
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 wh at 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:  
 
Acceptable  
 
Declaration of competing interests  
Please c omplete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five years received reimbursements, fees, funding, or salary from an 
organisation that may in any way gain or lose financially from the publication of this 
manuscript, either now or in the future?  
 
2. Do you hold any stocks or shares in an organisation that may in any way gain or lose 
financially from the publication of this manuscript, either now or in the future?  
 
3. Do you hold or are you currently applying  for any patents relating to the content of the 
manuscript?  
 
4. Have you received reimbursements, fees, funding, or salary from an organization that 
holds or has applied for patents relating to the content of the manuscript?  
 
5. Do you have any other financial c ompeting interests?  
 
6. Do you have any non -financial competing interests in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare that I have no competing interests' 
below. If your reply is yes to any, please give details below.  
 
I declare that I have no competing interests  
 
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to the editors, which will not be published.  
 
I agree to the open peer review policy of the journ al