Microbiological Evaluation of Upper Respiratory Tract Specimens in Patients with Plaque Psoriasis and Psoriatic Arthritis: A Retrospective Study

Psoriasis is a chronic immune-mediated skin disease associated with systemic inflammation and multiple environmental triggers, including microbial colonization and infections. However, the relationship between upper respiratory tract microorganisms and the clinical characteristics of plaque psoriasis and psoriatic arthritis remains incompletely understood. This retrospective study analyzed 624 patients with plaque psoriasis, including mild and moderate-to-severe disease, and psoriatic arthritis who presented with upper respiratory tract symptoms and clinical signs suggestive of pharyngeal involvement. Upper respiratory tract swabs were evaluated using culture-based methods. Clinical and inflammatory parameters, including disease severity assessed using the Psoriasis Area and Severity Index (PASI), systemic inflammation assessed using C-reactive protein (CRP), body mass index (BMI), age, sex, and smoking status, were analyzed. All patients were evaluated prior to initiation of systemic antipsoriatic treatment. Overweight and obesity were prevalent and were associated with higher CRP levels across clinical groups. Culture-positive results were identified in 247 patients, yielding 275 isolates, while 377 patients had culture-negative results with physiological flora only. The distribution of the most frequently isolated microorganisms was broadly similar across clinical subgroups, with limited variation according to psoriasis severity or psoriatic arthritis status. Multivariable analysis identified CRP and PASI as the most consistent factors associated with culture positivity in selected subgroups, with evidence of an interaction between psoriasis severity and systemic inflammatory burden. No consistent associations were observed between specific microorganisms and clinical measures of disease severity. Overall, systemic inflammatory and metabolic parameters showed more consistent associations with culture-positive pharyngeal findings than individual culture-detectable microorganisms. Given the retrospective design, symptom-based inclusion, and absence of a contemporaneous control group, these findings should be interpreted as descriptive and associative rather than causal. Prospective controlled studies using standardized sampling and culture-independent methods are needed to clarify the clinical significance and temporal relationship between upper respiratory tract microbial findings and psoriasis activity.