Incidence, microbiology, and patient characteristics of skin and soft-tissue infections in a U.S. population: a retrospective population-based study

Table 5 Risk factors for S. aureus and methicillin-resistant S. aureus skin and soft tissue infection episodes, Kaiser Permanente of Northern California, 2009-2011 ^a

	Adjusted odds ratio (95% CI)^b
	Among all episodes with a culture (n = 108243)^c	Among episodes positive for S. aureus(n = 47518)^d
Characteristic	Odds of S. aureusvs. not S. aureus	Odds of MRSA vs. MSSA
Gender
Female	0.86 (0.84,0.88)	1.04 (1.00,1.09)
Male	ref	ref
Age (years)
Under 5	3.89 (3.64,4.14)	1.28 (1.17,1.40)
5- < 18	2.64 (2.52,2.78)	0.79 (0.73,0.85)
18- < 50	1.91 (1.83,1.98)	1.11 (1.04,1.18)
50- < 65	1.40 (1.34,1.46)	1.03 (0.96,1.10)
65+	ref	ref
Race/Ethnicity
Asian	1.02 (0.98,1.06)	0.73 (0.68,0.78)
African-American	1.02 (0.98,1.07)	1.79 (1.67,1.92)
Hispanic	1.05 (1.01,1.08)	1.24 (1.18,1.31)
Native American	1.11 (0.95,1.30)	1.16 (0.92,1.46)
Multiracial	0.95 (0.89,1.02)	1.01 (0.91,1.13)
White	ref	ref
Diabetes status
Diabetes	0.93 (0.90,0.97)	0.75 (0.71,0.80)
No diabetes	ref	ref
Census Block Income Quintile
Unknown	1.16 (1.10,1.23)	1.27 (1.17,1.38)
1st (lowest income)	1.17 (1.12,1.22)	1.42 (1.33,1.51)
2nd	1.13 (1.09,1.18)	1.25 (1.17,1.34)
3rd	1.08 (1.03,1.12)	1.15 (1.08,1.22)
4th	1.02 (0.98,1.07)	1.12 (1.05,1.20)
5th (highest income)	ref	ref
Type of SSTI
Carbuncle and furuncle	1.33 (1.26,1.40)	1.22 (1.14,1.30)
Impetigo	1.03 (0.97,1.09)	0.16 (0.14,0.18)
Other infections of the skin	1.06 (1.00,1.11)	0.55 (0.51,0.59)
Folliculitis	0.87 (0.83,0.91)	0.50 (0.46,0.53)
Other SSTI	0.48 (0.42,0.53)	0.68 (0.56,0.82)
Cellulitis and abscess	ref	ref

^a CI = 95% confidence interval; MSSA = methicillin-sensitive S. aureus; MRSA = methicillin-resistant S. aureus; ref = reference group for other odds ratios within characteristic.
^bOdds ratios estimated using multivariate logistic regression. A separate model was run for each column in the table. For both models the independent variables were gender, age, race/ethnicity, diabetes status, income quintile based on census block, and type of SSTI.
^c The analytic dataset had one record per SSTI episode with a microbiologic test, and the dependent variable was whether or not the test was positive for S. aureus. Specimens may have been positive for other organisms or no organism may have been identified. Episodes without a microbiologic test were not included in the model.
^d The analytic dataset had a record for each SSTI episode that tested positive for S. aureus. The dependent variable was whether or not the isolate was methicillin-resistant.

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