The Impact of Antibiotic Therapy on Psoriasis Patients with Streptococcal Infection

Academic Background

Psoriasis is a chronic, relapsing inflammatory systemic skin disease with a global prevalence of around 2%-3%. Although its pathogenesis is not fully understood, studies suggest that bacterial, viral, and fungal infections may induce or exacerbate psoriasis. In particular, the association between Group A β-hemolytic Streptococcus (Streptococcus pyogenes) and psoriasis has been widely investigated. Many patients report that the onset of psoriasis is associated with streptococcal throat infections, especially in both children and adults. However, the exact impact of streptococcal infection on the course of psoriasis remains unclear, and the role of antibiotic therapy in psoriasis management is still controversial.

To address this issue, researchers led by D. Bonciani conducted a prospective study to evaluate the impact of streptococcal infection on the course of psoriasis and to investigate the effectiveness of systemic antibiotic therapy in psoriasis patients with concurrent streptococcal infection.

Source of the Paper

This paper was collaboratively completed by researchers from multiple institutions in Italy, including the Department of Dermatology at the University of Florence, the Microbiology and Virology Unit at Careggi University Hospital, and the Rare Skin Diseases Unit at Piero Palagi Hospital. The paper was published in 2025 in the Journal of Dermatology under the title “The Impact of Antibiotic Therapy in Psoriasis Patients with Active Streptococcal Infection: A Prospective Study.”

Research Process

1. Patient Recruitment

The study was conducted at a psoriasis center in Florence, Italy, and enrolled 155 psoriasis patients. Inclusion criteria included: age under 80 years, diagnosis of mild to moderate psoriasis, and the ability to provide written informed consent. Exclusion criteria included: pustular or erythrodermic psoriasis, concomitant psoriatic arthritis, history of spontaneous remission of psoriasis, history of antibiotic allergy, pregnancy or breastfeeding, and history of other immune-mediated diseases.

2. Disease Assessment

All patients underwent Psoriasis Area and Severity Index (PASI) scoring at enrollment, which was repeated at follow-up visits (1 month, 6 months, 12 months, and 18 months).

3. Streptococcal Infection Detection

Each patient underwent throat swab culture and anti-streptolysin O (ASO) titer testing. Throat swabs were cultured on Columbia blood agar plates and Group A selective agar plates, with bacterial strains identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). An ASO titer greater than 200 IU/ml was considered positive.

4. Patient Treatment and Follow-Up

Patients with positive throat swabs received systemic antibiotic therapy (amoxicillin, clarithromycin, or clindamycin based on susceptibility testing) alongside topical psoriasis treatment (including betamethasone and calcipotriol gel). Patients with negative throat swabs received only topical treatment. All patients were followed up at 1 month, 6 months, 12 months, and 18 months to evaluate clinical response and recurrence.

Main Findings

1. Prevalence of Streptococcal Infection

The study found that the detection rate of streptococcal infection in psoriasis patients was 25.5%, significantly higher than the 12.7% rate in the healthy control group. This suggests that psoriasis patients are more susceptible to streptococcal infections.

2. Changes in PASI Scores

At the 1-month and 6-month follow-ups, PASI scores significantly decreased in ASO-positive patients. However, there was no significant difference in the reduction of PASI scores between patients who received antibiotic therapy and those who did not. At 18 months, the antibiotic group showed an average PASI score reduction of 84.4%, compared to 76.0% in the non-antibiotic group, but the difference was still not statistically significant.

3. PASI75 and PASI90 Response Rates

There was no significant difference in the rates of achieving PASI75 (≥75% improvement) and PASI90 (≥90% improvement) between the antibiotic-treated and non-treated groups.

Conclusion

The study showed that although streptococcal infections are more common in psoriasis patients, systemic antibiotic therapy did not significantly improve the severity of psoriasis. This finding challenges the traditional use of antibiotics in psoriasis management and highlights the need for further research to clarify the complex relationship between infection and psoriasis.

Research Highlights

1. Association Between Streptococcal Infection and Psoriasis: The study confirmed the high detection rate of streptococcal infections in psoriasis patients, providing new evidence for the association between infection and psoriasis.
   
2. Controversy Over Antibiotic Therapy: The results show that antibiotic therapy did not significantly improve psoriasis severity, questioning current treatment strategies.
   
3. Long-Term Follow-Up: The study provided more comprehensive data on the effects of antibiotic therapy through 18 months of follow-up.
   

Research Value

This study provides important clinical evidence for the treatment of psoriasis, suggesting that the value of antibiotic therapy in psoriasis management is limited. At the same time, the study emphasizes the need for larger-scale and longer-follow-up research to further clarify the relationship between infection and psoriasis and to provide stronger guidance for clinical treatment.

Additional Information

The study was funded by the Italian Ministry of Health under project number 16RFAB. Additionally, the research team explored the potential role of streptococcal superantigens in the pathogenesis of psoriasis, providing direction for future research.