Reviewer's report
Title:Differences in patterns of high-risk human papillomavirus infection between
urban and rural low-resource settings: cross-sectional findings from Mali
Version: 2Date:24 September 2012
Reviewer: Paolo Giorgi Rossi
Reviewer's report:
The paper presents a very well conducted study and is very well written. The
conclusions are interesting and honest.
The main limitation of the study is the small sample size that strongly limits the
statistical power and the interpretation of findings.
I have only few major comments and some minor essential revisions:
Major compulsory revisions
1. The tables are difficult to interpret. They could be improved grouping the
variable and making clearer the comparison (table 2 and table 4).
2. The abstract conclusions over-interpret the results (“the factors that predict
HR-HPV…”). Please make the abstract and paper conclusions more consistent:
the very interesting conclusion that very high prevalence “may erode” the effect
of other risk factors is much more plausible that the real determinants changes.
Minor compulsory.
1. All over the paper: the way you measured the prevalence of HR HPV is really
a standard method, you do not need to use “correlate of infection” but simply
infections and, when you present a proportion, prevalence of infection.
2. Key words: I would say “prevalence” and “HPV infection”, not “HPV DNA
probe”.
Abstract
3. The background about vaccine implementation is not essential for the abstract,
while it is more interesting to highlight why the difference between rural and
urban is “a priori” interesting.
Introduction
4. The aim of the paper is described differently in the introduction and in the
abstract. I prefer the abstract version.
5. The study design changed from cross sectional studies to “pilot” studies. I
suggest to drop “pilot”.
Methods
6. Recruitment: please insert the dates of recruitment (beginning and stop) of the
two studies. I suggest to insert a box describing the characteristics of the two
studies and relative samples.
7. Please report the source of information for exclusion criteria (self reported,
clinical records or a mix, how did you described the conisation if self reported?).
8. Data management and statistical analysis: pag 9 last line: “very few data are
missing” it is not clear if it is refereed to income, to continuous variables or to all
variables. Furthermore, this is a result, but it is not reported in table 1. Please
report the missing values in table 1 (may be in foot notes) and drop this sentence
from the methods.
Results
9. It could be easier to follow the text if you present the variable in the same
order in the text and in the tables. I suggest to group the variable in the table
according to a conceptual framework: individual and socio economic status,
variables linked to the sexual behaviours (marital status polygamy, number of
pregnancy…), proper sexual behaviours (sexual debut, number of partners…),
finally condom use and screening.
10. Pag 12 second par: the description of the different association between age
at first intercourse and HPV infection in rural and urban population is confusing. I
think that it could be reported in a shorter and clearer way simply explaining that
in urban the relation is strong, while in urban is not present at all.
11. In my opinion it would be important to see the stratified model (table 3) for
urban and rural, the main objective of the paper is this one and the multivariate
analysis is appropriate to see if the determinants differ. If it is impossible because
the model does not converge, please declare it.
Discussion
12. Pag 13, First line: I suggest to avoid the word “dynamics”. As you explain
clearly and in a clever way at pag 15, in rural areas the prevalence is so high that
some association between proxies of sexual behaviours and infections cannot be
seen, it may be a sort of ceiling effect. If your interpretation is right (and it is
exactly what I supposed looking at your tables before reading the discussion, so I
perfectly agree with your interpretation) the dynamics of infections are the same,
what is changing is the resulting picture of prevalence: as in an over exposed
photo we see all the groups at a sort of maximum of prevalence.
13. Pag 13 “geographic setting” first sentence: I would say that prevalence of
most of the risk factors is actually higher in rural areas, but this only partially
explain… Furthermore something explaining the “underlying phenomenon” could
be the background prevalence of the community, this could be due to historical
reasons both behavioural or stochastic (founder effects).
14. Pag 14 line 9-12: very clever!
15. Other risk factors. This paragraph is poor: for many variables the sample is
not over-exposed: n. of partners, income, instruction, marital status and
polygamy. I think that the lack of association with all these variables is worth of
note for two reasons: socioeconomic status is associated in many context if in
Mali it is not can be highlighted; the lack of association with many proxies of the
sexual behaviours suggest that in your context these “social markers” usually
used as surrogate of the sexual behaviours are not good proxies.
16. Pag 15 “effect of high prevalence…”: very good paragraph.
17. Pag 17 line 3: “HPV behaves differently”, see first comment on discussion:
according to your interpretation is not the HPV that changes behaviours, but the
cross-sectional picture in a very high prevalence that probably is different and
loss all its contrast.
18. Limits: please discuss the problems of statistical power, not only in terms of
multiple testing.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I declare that I have no competing interests