PONE-D-20-32212

Sexually transmitted infections and behavioural factors associated with risky sexual practices among female sex workers: a cross sectional study in a large Andean city

PLOS ONE

Dear Dr. Llangarí,

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #1: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

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Reviewer #1: No

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Reviewer #1: Yes

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5. Review Comments to the Author

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Reviewer #1: This study aims to describe risk factors for risk factors for risky sexual practices and prevalence of STI in a population of female sex workers in Quito, Ecuador. This is an important and understudied topic but challenging to study due to the social standing and limited resources of this population. The authors should consider a major revision to the manuscript highlighting the major limitations of these data.

Major comments:

Study aims:

The study aims in this manuscript are not well described. Outlining specific aims and describing the variables and statistical analyses required for each aim will make the study much clearer. This appears to be a descriptive or exploratory study. If that is the case, this should be stated explicitly. Furthermore, the rationale for the exposures and outcomes in this study does not seem well supported. For example, why would previous STI be a risk factor for current risky sexual practices? Would the relationship be the other direction, with RSP causing STI? If the authors hypothesize previous STI lessens the risk of current RSP, this should be stated. In fact, justification for all associations tested should be included.

On the other hand, if this is solely a descriptive study, multivariable regression and other inferential statistics may not be appropriate. However, given this is a convenience sample, the authors have to be very cautious in their interpretations of prevalence.

Sampling:

The manuscript states a convenience sample was used and “cases were recruited through contacts with the association of sex workers in Quito.” There are several things that need to be clarified regarding the sampling methods. First, it is unclear why the word “cases” was used here as not everyone, presumably, was a case. Perhaps the authors intended to use the word participants. In addition, it is unclear how these female sex workers were recruited. More detail needs to be added, such as whether this was a snowball sampling method or something similar. Although these data may not exist, it would also be helpful to know how many women were approached and how many declined. Finally, what is meant by association of sex workers? Is this one organization to which registered all sex workers belong? If so, were all sex workers given an opportunity to participate? If not, what was the strategy for engaging this association? Did the researchers send a formal letter or approach the offices in person? In addition, the manuscript states samples were collected as the women attended a medical consultation required to validate their IHC during the last quarter of 2017. Does this mean only women who had a scheduled medical consultation during this time were eligible to participate? Were the samples collected as part of the routine exam or as an additional measure collected during the study? Much more detail is needed in this section.

Measurement of exposure and outcome:

More detail is needed regarding the collection of data on the exposures. Were they all collected via a self-reported questionnaire? Or were things like FSW association membership collected from other records? Why wasn’t previous STI validated with medical records if the women were attending a clinic? Were the medical records unavailable to the researchers? The authors mention in one sentence that they’re exploring variables associated with being a FSW and then elsewhere they discuss RSP as an outcome variable. Moreover, the authors have not presented a theoretical (or otherwise) justification for studying age or leaving the city for sex work as it relates to membership in a FWS organization.

STIs are associated with a great deal of stigma and may not be reported reliably. Self-reported RSP suffers from the same limitations. Social response/social desirability bias and recall bias may be of concern here. The authors mention this briefly in the limitations section of the conclusion but don’t discuss how this may impact their results. Would this be differential or non-differential misclassification? In other words, would those with STI be more or less likely to report RSP? This should be discussed.

Statistical methods:

As stated above, estimating prevalence from a convenience sample is highly problematic, particularly given we don’t know the characteristics of the entire population and whether these women are representative of all sex workers in Quito.

The authors need to provide more detail about how they conducted the regressions and how they constructed Table 1. Why are the n’s so much greater for some variables than the women who participated in the study? What variables were included in the adjusted OR? How were those variables selected? How was missingness of variables handled?

Finally, why were t tests for age only done for FSW membership and RSP? In addition, were homogeneity of variance and normality considered?

Conclusions:

The authors discuss how membership in an FSW may have affected their results as these sex workers are less likely to work in regulated brothels. This information should be in the introduction as it is important. Also, there is no discussion of why previous report of STI is associated with RSP but treatment for STI is not. Finally, the incidence of various STIs in this sample is somewhat low. This is good news. The authors should consider implications for practice/policy with regard to organized/legal sex work in the country as well as similar countries with legal sex work.

Minor comments:

There appear to be some word spacing and formatting issues throughout the manuscript. For example, sometimes there is a space between the citation and sometimes there is not. Also, some words have several spaces between them and others only one.

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Reviewer #1: No

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Sexually transmitted infections and factors associated with risky sexual practices among female sex workers: a cross sectional study in a large Andean city

PONE-D-20-32212R1

Dear Dr. Llangarí,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Andrew R. Dalby, PhD

Academic Editor

PLOS ONE

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