Reviewer’s report
Title: 
TRICHOMONAS VAGINALIS AS A RISK FACTOR FOR HUMAN
PAPILLOMAVIRUS: A STUDY WITH WOMEN UNDERGOING
CERVICAL CANCER SCREENING
Version: 
1 
Date: 
25 Nov 2020
Reviewer's report:
This paper is a cross-sectional study in women from San Luis, Brazil measuring
the prevalence of TV and HPV and the association with demographic,
sociological and biological cofactors. While this is an interesting topic of
investigation, and the sample size is large, the analytic plan is confusing. Tables
1, 2 and 3 are univariate analyses of factors associated with TV infection but
Table 4 is a multivariate analysis of factors associated with HPV infection, and
they did not present a univariate analysis of HPV infection or a multivariate
analysis of TV infection. This disjunction in the types of analyses performed is
confusing and is a major weakness of the paper. It seems like 2 parallel analyses
could be performed: uni- and multi-variate analyses of cofactors of TV infection,
and uni- and multi-variate analyses of risk factors of HPV. The latter analysis
(HPV infection) is less novel as it has been done by many groups in many
locations. Multivariate analysis to identify independent correlate of TV infection
is more novel. But this was not done. Adding to the confusion, the first
paragraph in the Results refers to data in Table 1 that is not in Table 1 but is in
Table 3. Why is Table 3 a separate table and not included in Table 2? 
In the Abstract and in several places in the text, the authors refer to "previously
identified cytological changes". This is confusing as it suggests they were not
using the results from the concurrently collected cytology samples. Please
clarify. 
In the statistical methods it states that "For multivariate analysis of the data, a
hierarchical model of binary logistic regression in six levels was built, in which
all variables were forced into the equation" with "level 6 , occurrence of HPV".
However, in Table 4 the analysis is looking at covariates of HPV infection.
Therefore the description of the methods for the multivariate analysis doesn't
make sense, as HPV would not have to be forced in. Also the title of Table 4 is
confusing because it doesn't indicate that it is a multivariate analysis of the
cofactors of HPV infection. Given the Tables that preceded it, I expected it to be
a multivariate analysis of TV infection. 
The section in the discussion on oral contraceptive use focuses on mechanisms
by which OC use could increase the risk of TV. However, the results in Table 2
point to the opposite conclusion: OC non-use was associated with a risk of TV.
The data in Table 4 do show that OC use was associated with increased risk of
HPV, the opposite of the association with TV. This raises again the question of
what is their primary analysis: correlates of TV infection, or correlates of HPV
infection? The association of TV with OC non-use suggests that there are
unmeasured confounders of risk for TV, perhaps non-use of any form of
protection (analogous to non-use of condoms), number of recent sex partners, etc
that explain the association. Missing from the manuscript is the analysis to show
whether OC non-use remains an independent risk factor for TV in multivariate
analysis. 
Re the power calculation the Methods states: "The sample size was calculated
considering a prevalence of 11.2% of women with TV [2], a power of 90% and a
5% significance level" but doesn't state what the study was powered to detect? A
more explicit statement of the association that the authors were testing is needed
and might help to frame the manuscript. 
Given the surprisingly high prevalence of HPV + results (46%), I assume they
are measuring both high- and low-risk HPV types? More detail about the HPV
PCR assay would be helpful: does the cocktail include low-risk and high-risk
types? how many HPV types were measured? what controls were included for
QA? 
The rate of cytological abnormalities is unusually high (67%). What would the
rate be if limited to diagnoses with higher predictive values for cancer precursor
lesions eg HSIL, ASC-H, AGC, AIS? And if this limitation is applied, does the
association between TV and cytological abnormalities still hold? It is possible
that the association they are observing has to do with nonspecific cytological
abnormalities such as ASCUS resulting from TV-associated inflammation, rather
than abnormalities associated with events related to carcinogenesis.
Minor edit:
In the 3rd paragraph of the Introduction they state that 'The incidence of HPV is
greater than 528,000 cases per year…' I believe they mean cervical cancer not
HPV. 
The second paragraph in the Results section describes the results in Table 1
without referring to the Table itself.
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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?
No
Are the methods sufficiently described to allow the study to be repeated?
Yes
Is the use of statistics and treatment of uncertainties appropriate?
No
Is the presentation of the work clear?
No
Are the images in this manuscript (including electrophoretic gels and blots) free
from apparent manipulation?
Yes