Reviewer ’s report  
 
Title: Vaginal douching in Zambia: A risk or benefit to women in the fight against cervic al cancer:  
A retrospective cohort study  
 
Version: 1 Date: 09 May 2019  
 
Reviewer: Katie O'Brien  
 
Reviewer's report:  
 
Vaginal Douching and Cervical Cancer in Zambia  
 
I read this article with great interest, as this is an understudied topic and it seem s particularly 
relevant to a country like Zambia where both douching prevalence and cervical cancer incidence 
are very high. Overall I liked the article and I think the findings are very interesting and worthy of 
publication. I thought the authors did a gr eat job of fitting their work into the greater literature and 
have a fair interpretation of what their results mean. However, I do have a some concerns that I 
would like to see addressed.  
 
Major concerns  
1. I would have liked to see more information on th e study sample. I know that it has been 
published on before, but the manuscript is missing a lot of key information, including how 
information on douching exposure and the covariates of interest were assessed, including the 
timing relative to when the VIA was performed. I also would have liked to have more information 
on who attends the screening clinics so that I could better understand how this sample is 
representative of the Zambian population. I additionally noticed that one key eligibility criteria - 
having at least one sexual partner - was not adequately described in the methods, which leads me 
to question what else may have been omitted.  
 
2. The authors examine what type of douching is associated with cervical lesions, but never give 
us estimates for ever versus never, which I think is of primary importance. I also expected to see 
never douching as the referent group for the comparison of t ypes of douche used. Point of 
clarification: douching with plain water is still douching if it involves a pressure system/ tubing, 
yes? 
 
 
3. There are some concerning errors in the only full paragraph on Page 6. First of all, I don't think 
women older than 49 are included, yet age groups 45 -54 and 55 or older are both mentioned. 
Secondly, the current interpretation of the education category %s is incorrect: It should be that 
among those who douched, 41% had a secondary education and 36% had a primary educati on. 
(Rather than the % who douched among those with a secondary education, as described.)  
 
4. Tables 1 -3 could easily be combined. Table 2 could even be eliminated entirely, as the numbers 
are directly calculable from the n's provided in Table 1 and the e stimates are not even discussed in 
the results. Further, since this is an observational study, I would assume that the effect estimates 
are subject to some confounding and am unsure of how to interpret the crude estimates anyway. 
Finally, it is not necessa ry to include both the 95% confidence intervals and the p -values: the 95% 
CI contains all of the information in the p -value, along with extra information about the precision 
of the estimate.  
 
5. For variables that are continuous (e.g. age, number of sex pa rtners, age @ debut, income), ORs 
for the continuous form of the variable and/or trend tests would help with interpretation.   
 
6. Table 5 could also be greatly reduced. Although the initial analysis is more about identifying 
what factors predict whether o r not a woman douches, the second analysis is more directly about 
the association between douche and cervical lesions. As discussed above, I think the primary focus 
should be on ever vs. never douche with a secondary analysis on type of douching. The effec t 
estimates for the other covariates are less interpretable in the current form as they are likely not 
appropriately adjusted for. For example, the association between age and cervical lesions cannot 
be confounded by any of the other factors in the table b ecause nothing affects age. There may be 
other key covariates/confounders of the HIV -cervical lesion or occupation -cervical lesion 
associations that are not included here, making those difficult to interpret as well.  
 
Minor comments:  
 ▪ I noticed that a lo t of women are missing HIV status. Normally I would discourage 
having a "missing" category in the tables/ as a covariate, as this results in a heterogenous category 
of people that it is not appropriate to perform statistical tests on as a group. However, s ince so 
many women are missing this information, I understand why excluding this women is not a 
reasonable approach. That being said, I think you need to acknowledge this as a limitation in the 
discussion. If you can think of a reasonable alternative (impu tation, exclusion of this variable from 
multivariable analyses), that might be informative, please consider adding that as a sensitivity 
analysis.  
 ▪ In the first paragraph of the results section, please provide %s as well as the n's. 
The %s are easier to make sense of.  
 ▪ An OR of 1.6 should be interpreted as 1.6 AS likely not 1.6 times MORE likely 
(see page 8).  
 ▪ Table 4 could be omitted. Model selection methods are inherently biased and it adds 
no extra information to what is already seen in the previo us tables. If kept, it might be helpful to 
re-frame as an attempt to build a predictive model for douching, rather than trying to interpret each 
covariate estimate on its own.  
 ▪ The conclusions are very circumspect (e.g. "include messages to sensitize wom en 
against douching"). I'd prefer to see something a bit more direct (e.g. "public health messaging 
should describe the possible health risks of douching") while still avoiding causal language.  
 
Are t he 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.  
 
Yes 
 
Are you able to assess any statistics in the manus cript or would you recommend an additional 
statistical review?  
If an additional statistical review is recommended, please speci fy what aspects require further 
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Acceptable  
 
 
 
 
 
 
 
Declaration of competing interests  
Please complete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five years received reimbursements, f ees, 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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4. Have you receiv ed reimbursements, fees, funding, or salary from an organization that holds 
or has applied for patents relating to the content of the manuscript?  
 
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If your reply is yes to any, please give details below.  
 
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