Objectives: Nasal carriage of Staphylococcus aureus and its superantigens (SAg) seem to be a risk factor disease exacerbation in granulomatosis with polyangiitis (GPA). We investigated the association between the presence of SAg in nasal swabs and activity of disease in GPA patients also taking into account correlation with an antimicrobial treatment.
Methods: In a prospective study of a total of 150 GPA patients hospitalised in the period 2009-2016, nasal swabs were examined for the presence of Staphylococcus aureus and SAg. Subsequently, the association with disease activity was assessed.
Results: Of 362 Staphylococcus aureus-positive nasal swab cultures from 115 of the 150 patients, the presence of at least one SAg in 126 samples (34.8%) from 56 patients (48.7%) was found. Among the 17 patients with limited to subglottic stenosis (SGS) disease, SAg were detected in 6 cases (35.3%). We did not find a significant correlation between the presence of SAg and disease activity (p=0.986), although when individual SAg were analysed separatively, SED and TSST-1 were more frequently present in active disease. Additionally, the results of the analysis demonstrated a protective effect of trimethoprim/sulfamethoxazole (T/S) treatment (0R 0.52, p<0.0092) in GPA patients. Interestingly, GPA limited to SGS appeared as an unfavourable factor associated with disease activity (0R 1.84, p=0.05).
Conclusions: The association between staphylococcal SAg in nasal swabs and GPA activity is not evident. Multiple mechanisms that may lead to disease activation still need to be investigated.