Comment on: Strong site-specific association of pharyngeal cultures with the onset of psoriatic arthritis and psoriasis, regardless of pathogen: reply.

Abstract

Dear Editor, We thank Rubén Queiro-Silva for the letter and insightful comments [1] on our article: ‘Strong site-specific association of pharyngeal cultures with the onset of psoriatic arthritis and psoriasis, regardless of pathogen’ [2]. First, we would like to address the commenters’ questions regarding our methods. These are all addressed in the Methods section on follow-up in the published article. For additional clarity, we can confirm that each individual could contribute multiple exposed periods, so that the observation unit is the period following sampling. Thus, the study did not address the possibility of cumulative risk from multiple exposures in the same individual, which might indeed have resulted in an even stronger observed effect. Regarding other questions raised in the comment, we believe the text of the published paper speaks for itself: ‘When the same individual had multiple samples sent for culture from the same site within 30 days, they were treated as one exposure, using the date of the first sample as the index date, and they were considered positive if any sample was positive. In the case of multiple culture sites or different organisms being reported within 30 days, none were used in the analysis’. It should be noted that all these design decisions were intended to reduce the chance of spurious findings or associations.