Characteristics of Staphylococcus aureus colonization in patients with atopic dermatitis in Sri Lanka

Colonization of the skin of patients with atopic dermatitis (AD) by Staphylococcus aureus (SA) is associated with more severe disease.

To determine the association of SA colonization patterns and densities in lesional and nonlesional skin in patients with varying severities of AD, and to determine the antibiotic sensitivity patterns of SA isolates from Sri Lanka.

Skin and nasal swabs collected from 100 patients with AD and 120 controls were used to investigate the presence of SA. Severity of AD was graded using the Nottingham Eczema Severity Score. Colony counts were obtained for skin samples, and antibiotic sensitivity testing was performed in cases positive for SA.

Skin colonization was seen in 57 patients (57%) but in only 10 controls (8%). Lesional skin of most patients (52/57; 91%) had SA densities of > 300 colony-forming units/cm(2) . Colonization rates with SA significantly increased with increasing age (Spearman correlation coefficient R = 0.9, P < 0.05) and increasing duration of lesions in patients with AD (Spearman R = 0.87, P < 0.05). Isolates from eight patients (13.5%) were found to be methicillin-resistant S. aureus (MRSA). Only 6 isolates (10%) were susceptible to penicillin and 22 (37%) to erythromycin, while 28 (47%) isolates had erythromycin-induced resistance to clindamycin.

SA colonization rates were significantly associated with increasing age and severity of AD, and particularly with duration of lesions. Patients with severe disease were also more likely to be colonized with SA strains resistant to conventional antibiotics.