Table 3: Factors associated with acquisition of TB infection between November 2011 and November 2012.
| Variable† | No. (%) of participants* | Crude OR (95% CI)‡ | Adjusted OR (95% CI)‡§ | |
|---|---|---|---|---|
| Newly infected(n = 88) | Uninfected (n = 67) | |||
| Age, yr | ||||
| < 15 | 30 (34) | 45 (67) | Reference | Reference |
| 15-29 | 44 (50) | 17 (25) | 3.9 (2.1-7.1) | 5.5 (2.8-10.7) |
| ≥ 30 | 14 (16) | 5 (8) | 4.2 (1.5-12.0) | 5.2 (1.5-18.0) |
| Sex | ||||
| Male | 40 (45) | 31 (46) | Reference | Reference |
| Female | 48 (54) | 36 (54) | 1.0 (0.6-1.9) | 0.8 (0.4-1.8) |
| Tobacco smoking | ||||
| Not current smoker | 30 (34) | 40 (60) | Reference | Not in model |
| Current smoker | 58 (66) | 27 (40) | 2.9 (1.5-5.4) | |
| Annual personal income, $ | ||||
| < 20 000 | 55 (66) | 36 (56) | Reference | Not in model |
| ≥ 20 000 | 28 (34) | 28 (44) | 0.7 (0.3-1.5) | |
| Heating method | ||||
| Forced air | 81 (92) | 64 (97) | Reference | Not in model |
| Radiator | 7 (8) | 2 (3) | 2.8 (0.8-10.2) | |
| No. of people per room,¶ mean ± SD | ||||
| Among participants living with smear-positive person | 1.7 ± 0.6 | 1.1 ± 0.7 | 1.5 (0.9-2.3) | 1.8 (1.1-2.9) |
| Among participants not living with smear-positive person | 1.2 ± 0.5 | 1.3 ± 0.4 | 0.9 (0.7-1.1) | 0.9 (0.7-1.1) |
| Ventilation with heating on relative to median (1.66 air changes per hour)** | ||||
| < Median | 68 (77) | 51 (76) | Reference | Not in model |
| ≥ Median | 20 (23) | 15 (22) | 1.0 (0.4-2.6) | |
| Volume of living area relative to median (65.5 m3) | ||||
| < Median | 32 (36) | 31 (47) | Reference | Not in model |
| ≥ Median | 56 (64) | 35 (53) | 1.6 (0.7-3.6) | |
| Visited dwelling used for social activities | 47 (53) | 16 (24) | 3.7 (1.7-7.9) | 4.2 (1.8-10.1) |
| Lived with smear-positive person†† | 20 (23) | 2 (3) | 9.6 (2.4-38.0) | 4.7 (0.95-23.2) |
Note: CI = confidence interval, OR = odds ratio, SD = standard deviation, TB = tuberculosis.
*Except where noted otherwise. One participant who had moved after the outbreak and whose dwelling could not be accessed was excluded from multivariate analysis.
†Data missing on income (n = 8), heating type (n = 1), ventilation (n = 1) and volume of living area (n = 1).
‡CIs where OR excludes 1.0 are in bold.
§Final multivariate model included all listed variables, except where indicated, plus an interaction term between occupancy and living with a smear-positive person that was statistically significant (p = 0.006).
¶Interaction term between occupancy and living with a smear-positive person was significant in univariate analysis (p < 0.05). The crude and adjusted ORs are per 0.2-unit increment in the number of people per room. This scale was chosen because it corresponds to an increment of 1 occupant in a dwelling with 5 rooms (the median number of rooms). As an example of interpretation: among those living with a smear-positive person in a dwelling with 5 rooms, if we were to compare 2 participants who did not live together and whose dwellings differed in occupancy by 1 person, the unadjusted odds of newly diagnosed infection would be 50% higher (as the OD is 1.5) for the participant living in the home with the greater number of people per room.
**In the living area. Lowest ventilation measured in the living area was also not associated with infection (data not shown).
††Adjusted OR shows association between living with someone with smear-positive TB and newly diagnosed infection if living in a dwelling with 1.2 persons per room (chosen because it was the median number of people per room).