The persistence of intracellular Staphylococcus aureus in the sinuses: a longitudinal study.

Staphylococcus aureus (S. aureus) can reside within the sinonasal mucosa in chronic rhinosinusitis patients and causes recurrent infections. Within the host cell, S. aureus can evade host immune detection enabling its own survival. We hypothesise that S. aureus can persist within the sinonasal epithelium for a prolonged period without immune activation. Patients with chronic rhinosinusitis with nasal polyps (CRSwNP) undergoing two sinus surgeries were included. Immunohistochemistry and Haematoxylin and Eosin stains were used to determine intracellular S. aureus (ICSA) status and inflammatory cell count, respectively. One-way ANOVA and paired t-tests were performed for comparison between ICSA subgroups and within each subgroup, respectively. Histopathological specimens from 34 patients (68 procedures) were included. ICSA positivity (ICSA+) was seen in 43 specimens (63.2%) from 26 (76%) patients. 18 (52.9%) of those were ICSA+ in both operations while 8 (23.5%) patients were ICSA+ in only one of the operations. 8 (23.5%) patients were ICSA negative in both operations. There was no difference in the number of eosinophils, lymphocyte and neutrophils between ICSA subgroups. This study demonstrated that S. aureus is found intracellularly within CRSwNP tissue at multiple time points without an increase in the number of eosinophils, lymphocytes and neutrophils. This finding supports our hypothesis that ICSA is able to escape from host detection and resides within the sinonasal mucosa despite intense treatment.