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

ABSTRACT

OBJECTIVES: The objective of this study was to evaluate any association between culture site / culture result / pathogen and incident PsA or psoriasis. METHODS: Records of all samples sent for culture from a large population during a 3-year period were linked with nationwide registry data on diagnoses and death over a 15-year period. The main outcomes of interest were incident diagnoses of PsA and psoriasis, defined by International Classification of Diseases (ICD) codes. The effect of culture site, culture result (positive vs negative), and pathogen (Streptococcus vs negative culture) on the risk of developing PsA and psoriasis was calculated using Cox proportional hazards models adjusted for age and gender. RESULTS: A total of 313 235 bacterial cultures from 128 982 individuals were analysed. Comparing individuals with pharyngeal cultures to those with urine cultures, the hazard ratio for incident PsA was 8.78 [95% confidence interval (CI) 3.23, 23.91] and for incident psoriasis it was 8.00 (95% CI 5.28, 12.12). Most of the risk was concentrated in the first 50 days after the culture date. Increased risk was also found when comparing individuals with cultures from the pharynx with those with cultures from the nasopharynx and blood. An association with streptococci was not found, neither in the pharynx nor at any other site. A positive bacterial culture from any site was associated with reduced risk for both PsA and psoriasis. CONCLUSION: There is a strong site-specific association between pharyngeal culture samples and an increased risk of PsA and psoriasis, regardless of the pathogen. This may indicate that the site of infection, rather than the pathogen, is associated with increased risk.