What is the likely bacteria responsible for nasal colonization?

Nasal Colonization: Primary Bacterial Pathogen

Staphylococcus aureus is the most clinically significant bacteria responsible for nasal colonization, with approximately 20-30% of the general population serving as asymptomatic nasal carriers. 1, 2, 3

Epidemiology and Colonization Rates

• S. aureus colonizes the anterior nares in approximately 30% of the human population asymptomatically, either transiently or persistently 2, 3
• Among college-aged populations, nasal colonization rates of S. aureus are approximately 21-22% 1, 4
• Healthcare workers demonstrate nasal carriage rates of 26.1% for S. aureus and 6.1% for MRSA specifically 1
• Emergency department patients show slightly lower rates at 22.1% for S. aureus and 7.8% for MRSA 1
• MRSA accounts for approximately 35% of S. aureus nasal isolates in patient populations 1

Clinical Significance of Nasal Colonization

• A substantial proportion (82-86%) of S. aureus bacteremia cases originate from the patient's own nasal flora, establishing nasal colonization as a major endogenous source of systemic infection 5
• Blood isolates were clonally identical to nasal isolates in 82.2% of patients with S. aureus bacteremia in multicenter studies 5
• Nasal colonization increases the risk of subsequent opportunistic infections including surgical site infections, pneumonia, and life-threatening sepsis 3
• Among patients with recurrent furunculosis, S. aureus colonization in the anterior nares or perineum is the most important predisposing factor 6, 7

Other Nasal Colonizing Bacteria

While S. aureus is the primary pathogen of clinical concern, the nasal microbiome contains other bacteria:

• Coagulase-negative staphylococci colonize the middle meatus in approximately 35% of normal adults 1
• Corynebacterium species are found in 23% of middle meatal samples from normal adults 1
• Methicillin-susceptible S. aureus colonizes an additional 10-24% of individuals beyond MRSA carriers 8

Risk Factors for S. aureus Nasal Colonization

• Hemodialysis patients show significantly higher rates of MRSA colonization (p = 0.012) 1
• Lifestyle factors positively correlated with colonization include pet exposure, time spent in recreational facilities, musical instrument usage, and tobacco use 4
• Among household contacts of patients with CA-MRSA infections, 20% are colonized with MRSA, which is substantially higher than general population rates 8
• Within the same household, multiple strains of CA-MRSA may be present simultaneously 8

Clinical Implications for Decolonization

• For recurrent S. aureus infections, intranasal mupirocin ointment applied twice daily for the first 5 days of each month reduces recurrences by approximately 50% 6, 7
• Oral clindamycin 150 mg daily for 3 months is more effective, decreasing subsequent infections by approximately 80% 6, 7
• Treating household contacts in addition to the patient results in significantly fewer recurrences compared to treating the patient alone 6, 7
• Mupirocin is active against S. aureus and demonstrates no cross-resistance with other antimicrobial classes 9

Common Pitfalls

• Do not assume all nasal bacteria are pathogenic—coagulase-negative staphylococci and Corynebacterium species are common commensals 1
• Do not rely solely on topical decolonization without addressing systemic and environmental factors 6
• Do not overlook household contacts as potential reservoirs requiring concurrent treatment 6, 8
• Be aware that MRSA resistance to mupirocin occurs with greater frequency in methicillin-resistant strains, so susceptibility testing is appropriate prior to use 9