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Archived Comments for: Chlamydia trachomatis prevalence in undocumented migrants undergoing voluntary termination of pregnancy: a prospective cohort study

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  1. Comment on description of study design

    Nicola Low, University of Bern

    23 September 2009

    This study is described in the title as a prospective cohort study. It appears, however, to be two separate cross-sectional studies measuring prevalent chlamydia infection, with no follow up period.

    'The main feature of a cohort study is observation of large numbers over a long period with the comparison of incidence rates in groups that differ by exposure levels.' (Last JM. A Dictionary of Epidemiology. 4th Ed. Oxford, Oxford University Press, 2001.)

    In a cohort study of chlamydia infection, women would be enrolled prospectively and tested for chlamydia. If positive they would be treated and confirmed to be clear of infection. They would then be asked to be tested at one or more time points in the future. The incidence of new chlamydia infections per unit period of time would then be compared between women who were undocumented migrants or who were not.

    Competing interests

    No competing interests