Origin Sites of Staphylococcus aureus in Humans
Staphylococcus aureus primarily originates from the anterior nares (nostrils), which serve as the major reservoir in 20-40% of the general population, with secondary colonization sites including the perineum, axillae, throat, and skin. 1
Primary Colonization Sites
Anterior Nares (Nostrils)
The moist squamous epithelium of the anterior nares is the natural habitat and primary colonization site for S. aureus 2. This nasal carriage:
- Occurs in 20-40% of the general population 1
- Represents approximately 30% asymptomatic colonization rate 3
- Serves as the main reservoir from which the organism spreads to other body sites 4
Secondary Body Sites
S. aureus colonizes multiple additional anatomical locations 5:
- Perineal/inguinal areas: Most heavily colonized intact skin sites (100 to 10⁶ organisms/cm²) 5
- Axillae: Frequently colonized region 5
- Throat: Common carriage site 6
- Skin surfaces: Including trunk and upper extremities 5
- Subungual spaces (under fingernails): Significant reservoir, particularly in healthcare workers and patients with atopic dermatitis 7
- Vagina and rectum: Occasional carriage sites, particularly relevant in healthcare-associated transmission 8
Clinical Significance of Colonization Sites
Transmission Patterns
The anterior nares serve as the primary source for subsequent infections 1. From nasal colonization:
- Organisms spread to other body parts where they may remain commensal or cause infection 4
- In staphylococcal impetigo, pathogens are usually present in the nose before causing cutaneous disease 1
- Colonization precedes skin infection by approximately 10 days in streptococcal cases, though S. aureus follows a different pattern 1
High-Risk Populations
Certain populations show increased colonization rates at specific sites 5:
- Diabetic patients: Higher rates of intact skin colonization
- Dialysis patients: Increased S. aureus carriage
- Patients with chronic dermatitis: More extensive skin colonization
- Atopic dermatitis patients: 95.5% colonization rate, with correlation between nasal and skin-colonizing strains 7
Important Clinical Caveats
Recurrent Infections
For individuals with recurrent furunculosis, the only identifiable predisposing factor is typically S. aureus presence in the anterior nares or occasionally the perineum 1. This explains why:
- Nasal decolonization with mupirocin reduces recurrences by ~50% 1
- Oral clindamycin for 3 months decreases subsequent infections by ~80% 1
Environmental Shedding
Colonized individuals shed approximately 10⁶ skin squames containing viable microorganisms daily from normal skin 5, which explains why:
- Patient gowns, bed linens, and bedside furniture easily become contaminated 5
- Fomites can harbor organisms and facilitate transmission 1
Healthcare Implications
Healthcare workers can carry S. aureus in nose, anus, vagina, and on skin lesions, all of which have been linked to outbreak transmission 8. The perineal and inguinal areas typically harbor the highest bacterial counts on intact skin 5.