Table 1.
Demographics, Clinical Factors, and Bivariate Analysis of Risk Factors Associated With Colonization of the Index Patient by the Index Patient’s Infecting Strain Type
| Variable | All, n = 350 (%) | Colonized With Infecting Strain, n = 41 (%) | Not Colonized With Infecting Strain, n = 309 (%) | OR | 95% CI | P Value |
| Site | ||||||
| Chicago | 177 (51) | 22 (53) | 155 (50) | 1.15 | .60, 2.21 | .67 |
| Los Angeles | 173 (49) | 19 (46) | 154 (50) | … | … | … |
| Demographics | ||||||
| Gender | ||||||
| Female | 180 (51) | 26 (63) | 154 (50) | 1.75 | .89, 3.42 | .11 |
| Male | 170 (49) | 15 (37) | 155 (50) | … | … | … |
| Age | ||||||
| Older adult (>65 yr) | 15 (4) | 2 (5) | 13 (4) | 1.30 | .27, 6.22 | .74 |
| Adult (19–65 yr) | 180 (51) | 19 (46) | 161 (52) | Ref | … | … |
| Child (5–18 yr) | 55 (16) | 8 (20) | 47 (15) | 1.44 | .59, 3.50 | .42 |
| Younger child (<5 yr) | 100 (29) | 12 (29) | 88 (28) | 1.16 | .54, 2.49 | .71 |
| Ethnicity | ||||||
| African-American | 177 (51) | 24 (58) | 153 (50) | 1.20 | .34, 4.32 | .78 |
| Caucasian | 26 (7) | 3 (7) | 23 (7) | Ref | … | … |
| Hispanic | 121 (35) | 12 (29) | 109 (35) | 0.84 | .22, 3.23 | .81 |
| Other/mixed/unknown | 26 (7) | 2 (5) | 24 (8) | 0.64 | .10, 4.18 | .64 |
| Clinical factors | ||||||
| Charlson comorbidity score | ||||||
| Mean ± SD | 1 ± 2 | 1 ± 2 | 1 ± 2 | 0.92 | .78, 1.08 | .30 |
| Median (range) | 0 (0–14) | 0 (0–12) | 0 (0–14) | … | … | … |
| Comorbidities | ||||||
| Diabetes | 57 (16) | 5 (12) | 52 (17) | 0.69 | .26, 1.83 | .45 |
| HIV infection | 14 (5) | 0 (0) | 14 (14) | NA | NA | .39 |
| In the past 12 mo: | ||||||
| Had a previous skin infection | 217 (62) | 23 (56) | 194 (63) | 0.76 | .39, 1.46 | .41 |
| Undergone major surgery | 88 (25) | 12 (29) | 76 (24) | 1.27 | .62, 2.61 | .52 |
| Received dialysis | 8 (2) | 0 (0) | 8 (3) | NA | NA | .60 |
| Hospitalized | 172 (49) | 18 (44) | 154 (50) | 0.79 | .41, 1.52 | .48 |
| Days of hospitalization | ||||||
| Mean ± SD | 4 ± 18 | 3 ± 8 | 4 ± 19 | 0.99 | .97, 1.02 | .82 |
| Median (range) | 0 (0–320) | 0 (0–39) | 0 (0–320) | … | … | … |
| Any antibiotic exposure | 237 (67) | 24 (59) | 213 (69) | 0.64 | .33, 1.24 | .18 |
| Use of clindamycin | 35 (10) | 7 (18) | 28 (9) | 2.07 | .86, 5.09 | .16 |
| Use of TMP-SMX | 37 (11) | 3 (8) | 34 (11) | 0.65 | .19, 2.18 | .78 |
| Use of cephalexin | 17 (5) | 2 (5) | 15 (5) | 1.02 | .23, 4.65 | .99 |
| Use of immunosuppressant medications | 70 (20) | 9 (23) | 61 (20) | 1.15 | .52, 2.57 | .72 |
| Spent time living in a skilled nursing facility, rehabilitation center, or other type of group facility | 8 (2) | 2 (5) | 6 (2) | 2.68 | .52, 13.74 | .23 |
| Epidemiologic factors | ||||||
| Household density | ||||||
| Mean ± SD | 1.96 ± 1.08 | 1.94 ± 0.93 | 1.96 ± 1.10 | 0.99 | .73, 1.35 | .94 |
| Median (range) | 1.73 (0.40–9.0) | 1.66 (0.667–4.0) | 2.0 (0.40–9.0) | … | … | … |
| Homelessness in the past 12 mo | 14 (4) | 3 (7) | 11 (3) | 2.14 | .57, 8.01 | .22 |
| Cuts/scratches in the 30 d prior to index infection | 143 (41) | 19 (46) | 124 (40) | 1.29 | .67, 2.48 | .50 |
| Skin rash in the 90 d prior to index infection | 60 (18) | 14 (36) | 46 (16) | 2.97 | 1.44, 6.17 | .002a |
| Pets in the home, currently | 156 (45) | 15 (38) | 141 (46) | 0.702 | .36, 1.38 | .32 |
| Incarceration in the past 12 mo | 9 (4) | 0 (0) | 9 (5) | - | - | .60 |
| Illicit drug use in the past 12 mo | 34 (10) | 1 (2) | 33 (11) | 0.21 | .03, 1.57 | .15 |
| >1 sexual partner in the past 12 mo | 25 (12) | 3 (12) | 22 (12) | 1.02 | .29, 3.70 | .99 |
| In the past 3 mo: | ||||||
| Showered at least once a day | 39 (12) | 4 (11) | 35 (12) | 0.91 | .30, 2.71 | .99 |
| Shared make-up with others | 20 (7) | 2 (5) | 18 (7) | 0.76 | .17, 3.42 | .99 |
| Shared bar soap with others | 193 (57) | 25 (63) | 168 (56) | 1.32 | .67, 2.60 | .42 |
| Shared clothes with others with washing | 21 (6) | 3 (7) | 18 (6) | 1.25 | .35, 4.44 | .73 |
| Shared towels with others | 157 (46) | 21 (51) | 136 (45) | 1.30 | .67, 2.49 | .43 |
| Wore clothes more than once without washing | 166 (49) | 23 (58) | 143 (47) | 1.48 | .76, 2.87 | .25 |
| Hand-washing frequency after using the bathroom | ||||||
| Mean ± SD | 2.6 ± 0.78 | 2.6 ± 0.80 | 2.6 ± 0.78 | 1.01 | .66, 1.54 | .97 |
| Median (range) | 3 (0–3) | 3 (0–3) | 3 (0–3) | |||
| Household cleaning scaleb | ||||||
| Mean ± SD | 16 ± 8 | 17 ± 8 | 16 ± 8 | 1.18 | .62, 2.20 | .61 |
| Median (range) | 18 (0–35) | 18 (0–33) | 18 (0–35) | |||
| Use of a gym | 27 (14) | 5 (14) | 22 (9) | 1.56 | .55, 4.42 | .38 |
| Participation in contact sports | 83 (24) | 11 (27) | 72 (23) | 1.21 | .58, 2.53 | .62 |
| Goes to day care | 25 (19) | 1 (7) | 24 (21) | 0.27 | .03, 2.19 | .30 |
| Use of public facilitiesc | 76 (22) | 12 (29) | 64 (21) | 1.58 | .77, 3.27 | .21 |
| Strain-specific factors | ||||||
| Infecting strain type categorization by the CDC case definition | ||||||
| CA-MRSA | 111 (32) | 15 (37) | 96 (31) | 1.28 | .65, 2.53 | .92 |
| HA-MRSA | 122 (35) | 17 (42) | 105 (34) | Ref | ||
| CA-MSSA | 45 (13) | 3 (7) | 42 (14) | 0.50 | .15, 1.70 | .29 |
| HA-MSSA | 72 (20) | 6 (15) | 66 (21) | 0.63 | .26, 1.56 | .28 |
| ST8-MRSA-Mec IV-PVL strain type | 186 (53) | 29 (71) | 157 (51) | 2.33 | 1.15, 4.75 | .02 |
| PVL presence | 266 (76) | 33 (81) | 233 (75) | 0.74 | .33, 1.67 | .56 |
| SCCmec type IV | 220 (63) | 30 (73) | 190 (62) | 1.71 | .82, 3.54 | .17 |
| Other household members colonized with the infection strain type | 81 (23) | 21 (51) | 60 (19) | 4.36 | 2.22, 8.55 | <.001d |
Statistically significant relationships are bolded; NA indicates cannot be calculated due to zero cell.
Abbreviations: CA-MRSA, community-associated methicillin-resistant Staphylococcus aureus; CA-MSSA, community-associated methicillin-susceptible S. aureus; CDC, Centers for Disease Control and Prevention; CI, confidence inverval; HA-MRSA, healthcare-associated methicillin-resistant S. aureus; HA-MSSA, healthcare-associated methicillin-susceptible S. aureus; HIV, human immunodeficiency virus; OR, odds ratio; PVL, Panton-Valentine leukocidin; Ref, reference group; SD, standard deviation; TMP-SMX, trimethoprim-sulfamethoxazole.
Variable significant in multivariable analysis (OR, 2.9 [1.4–6.2]; P = .006).
Household cleaning is a measure of the frequency of cleaning for common household items, with higher values representing more frequent cleaning.
Use of public facilities is defined as use of a publicly available gym, locker room, shower, swimming pool, sauna, or Jacuzzi.
Variable significant in multivariable analysis (OR, 4.3 [2.1–8.6]; P < .001).