Studies have shown that psoriatic lesions are prone to Staphylococcal aureus (S. aureus) colonization. How lesional bacterial loads change over time with routine treatment for psoriasis has not been well characterized. 

To delineate the temporal dynamics of staphylococcal colonization on skin lesions of psoriasis patients under treatment and to identify host factors associated with the hypothesized changes, we prospectively enrolled 19 adult psoriasis patients who were clinically eligible for biologic treatment at a Dermatology Outpatient Clinic between May 2015 and February 2016. 

We repeatedly sampled patients’ bilateral post-auricular hairline, volar forearms, and the pretibial area every 4-6 weeks up to 16-20 weeks. We applied mixed effects Poisson regression models to assess time-constant and time-varying host characteristics and behaviors associated with lesional staphylococcal colonization. We also performed a nested case-control analysis to identify correlates with incident decolonization during treatment. Staphylococcal colonization status was determined by culture and methicillin-resistant strains were identified by the disk diffusion method. 

Baseline prevalence of cutaneous S. aureus colonization was 42%, half of which were by methicillin-resistant strains (21%). At 16 weeks post-treatment, the risk for cutaneous staphylococcal colonization decreased by 84% (adjusted odds ratio [aOR]: 0.16; 95%confidence interval [CI]: 0.04, 0.71). Current smoking status (aOR: 8.84), regular alcohol use (aOR: 2.98), disease duration (≥ 20 years, aOR: 11.3), and first-time biologic users (aOR:5.83) at baseline as well as clinical improvement of 75% or higher (PASI75, aOR: 0.25) at follow-up were significant host factors for (prevalent) staphylococcal colonization. After adjusting for matching and age, alcohol use (adjusted odds ratio [aOR]: 4.87; 95%CI: 3.15, 7.52) and achieving PASI75 (aOR: 0.18, 95%CI: 0.04, 0.77) were strongly associated with a higher and lower risk for incident decolonization in patients under routine psoriatic treatment. 

Cutaneous staphylococcal load could decrease over time with routine non-antibiotic treatment. Risky behaviors and individual disease characteristics were important correlates with staphylococcal colonization and decolonization in psoriasis patients.

Host characteristics and the temporal dynamics of Staphylococcus aureus colonization in psoriasis patients under routine treatment.