Table 4.
Bivariate Analysis of Risk Factors Associated With an Index Patient’s Infecting Strain Colonizing a Household Member in at Least 1 Body Site
| Variable | All, n = 812 (%) | Colonized With Index Infection Strain, n = 111 (%) | Not Colonized With Index Infection Strain, n = 701 (%) | OR | 95% CI | P value |
| Site | ||||||
| Chicago | 422 (52) | 54 (49) | 368 (53) | 0.99 | .94, 1.04 | .63 |
| Los Angeles | 390 (48) | 57 (51) | 333 (48) | … | … | … |
| Demographics | ||||||
| Gender | ||||||
| Female | 510 (63) | 63 (57) | 447 (65) | 0.96 | .92, 1.01 | .13 |
| Male | 294 (37) | 48 (43) | 246 (36) | … | … | … |
| Age | ||||||
| Older adult (>65 yr) | 36 (4) | 5 (5) | 31 (5) | 1.01 | .90, 1.13 | .85 |
| Adult (19–65 yr) | 492 (61) | 67 (60) | 425 (61) | Ref | … | … |
| Child (5–18 yr) | 175 (22) | 27 (24) | 148 (21) | 1.02 | .95, 1.08 | .59 |
| Younger child (<5 yr) | 109 (13) | 12 (11) | 97 (14) | 0.97 | .91, 1.03 | .33 |
| Ethnicity | ||||||
| African-American | 412 (51) | 53 (48) | 359 (51) | 1.06 | .97, 1.16 | .18 |
| Caucasian | 48 (6) | 3 (3) | 45 (6) | Ref | … | … |
| Hispanic | 300 (37) | 50 (45) | 250 (36) | 1.11 | 1.001, 1.22 | .03 |
| Other/mixed/unknown | 52 (6) | 5 (5) | 47 (7) | 1.02 | .91, 1.14 | .69 |
| Clinical factors | ||||||
| Charlson comorbidity score | ||||||
| Mean ± SD | 0 ± 1 | 0 ± 1 | 0 ± 1 | 0.98 | .96, 1.00 | .16 |
| Median (range) | 0 (0–7) | 0 (0–6) | 0 (0–7) | … | … | … |
| Comorbidities | ||||||
| Diabetes | 71 (9) | 9 (8) | 62 (9) | 0.99 | .91, 1.07 | .73 |
| HIV infection | 8 (2) | 1 (1) | 7 (2) | 0.99 | .82, 1.19 | .91 |
| In the past 12 mo | ||||||
| Had a previous skin infection | 197 (25) | 45 (41) | 152 (23) | 1.12 | 1.04, 1.19 | <.001a |
| Undergone major surgery | 59 (7) | 4 (4) | 55 (8) | 0.94 | .87, 1.01 | .07 |
| Received dialysis | 1 (0.12) | 0 (0) | 1 (0.14) | NA | NA | .99 |
| Hospitalized | 101 (13) | 15 (14) | 86 (13) | 1.01 | .93, 1.08 | .88 |
| Days of hospitalization | ||||||
| Mean ± SD | 0.5 ± 2 | 0.5 ± 2 | 0.5 ± 2 | 1.00 | .98, 1.01 | .93 |
| Median (range) | 0 (0–30) | 0 (0–21) | 0 (0–30) | … | … | … |
| Any antibiotic exposure | 248 (31) | 43 (39) | 205 (30) | 1.05 | .99, 1.11 | .11 |
| Use of clindamycin | 12 (2) | 4 (4) | 8 (1) | 1.22 | .89, 1.67 | .22 |
| Use of TMP-SMX | 11 (1) | 4 (4) | 7 (1) | 1.23 | .96, 1.58 | .09 |
| Use of cephalexin | 15 (2) | 7 (6) | 8 (1) | 1.39 | 1.06, 1.78 | .02b |
| Use of immunosuppressant medications | 78 (10) | 14 (13) | 64 (9) | 1.04 | .95, 1.14 | .42 |
| Spent time living in a skilled nursing facility, rehabilitation center, or other type of group facility | 19 (2) | 2 (2) | 17 (3) | 0.95 | .84, 1.07 | .41 |
| Epidemiologic factors | ||||||
| Household density | ||||||
| Mean ± SD | 2.0 ± 0.98 | 2.2 ± 0.92 | 2.0 ± 0.98 | 1.01 | .99, 1.04 | .33 |
| Median (range) | 2.0 (0.33–6.0) | 2.2 (0.71–6.0) | 2.0 (0.33–6.0) | … | … | … |
| Homelessness in the past 12 mo | 40 (5) | 5 (5) | 35 (5) | 0.99 | .89, 1.11 | .99 |
| Cuts/scratches in the 30 d prior to index infection | 308 (38) | 51 (46) | 257 (37) | 1.05 | .99, 1.11 | .07 |
| Skin rash in the 90 d prior to index infection | 87 (11) | 18 (17) | 69 (10) | 1.09 | .99, 1.18 | .06 |
| Pets in the home currently | 339 (42) | 47 (43) | 292 (42) | 1.01 | .95, 1.06 | .83 |
| Incarceration in the past 12 mo | 21 (3) | 3 (4) | 18 (3) | 1.02 | .87, 1.19 | .86 |
| Illicit drug use in the past 12 mo | 66 (11) | 11 (14) | 55 (11) | 1.05 | .96, 1.15 | .26 |
| >1 sexual partner in the past 12 mo | 73 (12) | 9 (12) | 64 (12) | 0.99 | .92, 1.07 | .80 |
| In the past 3 mo | ||||||
| Showered at least once a day | 131 (16) | 23 (21) | 108 (16) | 1.04 | .97, 1.11 | .32 |
| Shared make-up with others | 88 (12) | 13 (13) | 75 (11) | 1.01 | .93, 1.10 | .82 |
| Shared bar soap with others | 496 (63) | 67 (63) | 429 (63) | 1.00 | .95, 1.05 | .96 |
| Shared clothes with others without washing | 51 (6) | 8 (7) | 43 (6) | 1.03 | .94, 1.13 | .53 |
| Shared towels with others | 389 (48) | 55 (50) | 334 (48) | 1.02 | .97, 1.07 | .42 |
| Wore clothes more than once without washing | 400 (50) | 58 (53) | 342 (49) | 1.02 | .97, 1.07 | .42 |
| Hand-washing frequency after using the bathroom | ||||||
| Mean ± SD | 2.7 ± 0.62 | 2.7 ± 0.76 | 2.8 ± 0.60 | 0.97 | .92, 1.01 | .20 |
| Median (range) | 3 (0–3) | 3 (0–3) | 3 (0–3) | … | … | … |
| Household cleaning scalec | ||||||
| Mean ± SD | 17 ± 7 | 17 ± 8 | 17 ± 7 | 0.99 | .99, 1.00 | .17 |
| Median (range) | 18 (0–34) | 18 (0–29) | 18 (0–34) | … | … | … |
| Use of a gym | 87 (12) | 10 (10) | 77 (12) | 0.98 | .92, 1.05 | .59 |
| Participation in contact sports | 201 (25) | 33 (30) | 168 (24) | 1.04 | .98, 1.10 | .23 |
| Goes to day care | 30 (16) | 3 (10) | 27 (17) | 0.92 | .82, 1.02 | .10 |
| Use of public facilitiesd | 224 (28) | 32 (29) | 192 (28) | 1.00 | .96, 1.06 | .86 |
| Strain Specific Factors | ||||||
| Infecting strain categorization by the CDC case definition | ||||||
| CA-MRSA | 268 (33) | 39 (35) | 229 (33) | 0.95 | .88, 1.01 | .12 |
| HA-MRSA | 258 (32) | 52 (47) | 206 (29) | Ref | … | … |
| CA-MSSA | 100 (12) | 8 (7) | 92 (13) | 0.89 | .82, .97 | .008 |
| HA-MSSA | 186 (23) | 12 (11) | 174 (25) | 0.88 | .82, .94 | .003 |
| ST8-IV-PVL infection strain type | 442 (54) | 87 (78) | 355 (51) | 1.13 | 1.08, 1.19 | <.001e |
| PVL presence | 622 (77) | 95 (86) | 527 (75) | 1.07 | 1.01, 1.13 | .03 |
| SCCmec type IV | 503 (62) | 89 (80) | 414 (59) | 1.10 | 1.05, 1.16 | <.001 |
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 interval; 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; SCCmec type, staphylococcal cassette chromosome mec type; TMP-SMX, trimethoprim-sulfamethoxazole.
Variable significant in multivariable analysis (OR, 2.01 [1.31–3.08]; P = .001).
Variable significant in multivariable analysis (OR, 3.5 [1.3–9.5]; P = .01).
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, 3.0 [1.7–5.3]; P = .0002).