Site-specific pharyngeal culture samples, regardless of pathogen, are significantly associated with a higher risk for psoriatic arthritis (PsA) and psoriasis, according to study results published in Rheumatology.

Researchers aimed to determine the association between pharyngeal infections and onset of PsA and psoriasis.

The population-based cohort study included individuals who provided bacterial cultures that were collected over a 3-year period and linked to 15-year data on death and diagnoses from a national registry.


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The primary outcome of the study included International Classification of Diseases, Tenth Revision (ICD-10) code-defined incident diagnoses of psoriasis and PsA.

Age- and sex-adjusted Cox proportional hazards models were used to calculate the effect of culture site, result, and pathogen (streptococcus vs negative result) on the likelihood of developing PsA.

A total of 128,982 individuals contributing 313,235 bacterial cultures were included in the study. The most common culture sites were pharynx (12%), blood (14%), nasopharynx (23%), and urine (47%).

For individuals with pharyngeal vs urine cultures, the hazard ratio for incident PsA was 8.78 (95% CI, 3.23-23.91) and incident psoriasis was 8.00 (95% CI, 5.28-12.12), with the majority of risk occurring within 50 days of the culture date. The risk persisted after 50 days, but with a lower hazard ratio.

Pharyngeal vs blood and nasopharyngeal cultures were also associated with higher risk (HR, 9.51 for PsA; 5.80 for psoriasis). Researchers did not observe an association with streptococci in any site, though positive bacterial cultures were associated with lower risk for both PsA and psoriasis at any infection site.

Study limitations included uncertainty about the prevalence of undiagnosed, preexisting PsA among participants, lack of information on antibiotic use or other risk factors, inability to perform distinct subanalyses of inpatient and outpatient infections, and uncertainty regarding whether the observed correlations were applicable to milder pharyngeal infections.

The study researchers concluded that “a strong, site-specific association of pharyngitis with increased risk [for] PsA and psoriasis was found, regardless of pathogen type,” an association that “was not seen for RA.” Furthermore, the study researchers also noted “an association with a surrogate marker of clinically significant pharyngitis regardless of the pathogen” and suggest further research “to understand this association with pharyngitis more clearly, including analyzing the role of antibiotic use and individual viral pathogens.”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Thrastardottir T, Meer E, Hauksdottir A, et al. Strong site-specific association of pharyngeal cultures with the onset of psoriatic arthritis and psoriasis, regardless of pathogen. Rheumatology. Published online April 23, 2022. doi:10.1093/rheumatology/keac253