Volume 14, Number 7—July 2008
Research
Determinants of Cluster Size in Large, Population-Based Molecular Epidemiology Study of Tuberculosis, Northern Malawi
Table 1
Associations between patient characteristics and cluster size, Mycobacterium tuberculosis, bivariate analysis, Malawi
Characteristic | N | Cluster size, % |
Odds ratio (95% CI)* | p value | |||
---|---|---|---|---|---|---|---|
2–4 (n = 186) | 5–10 (n = 196) | 11–20 (n = 173) | >20 (n = 127) | ||||
Age, y | 0.05 | ||||||
<25 | 111 | 27.9 | 25.2 | 25.2 | 21.6 | 1 | |
25–34 | 266 | 24.4 | 26.3 | 27.8 | 21.4 | 1.1 (0.74–1.7) | |
35–44 | 160 | 26.3 | 32.5 | 25.0 | 16.3 | 0.87 (0.56–1.3) | |
>45 |
145 |
33.1 |
31.7 |
21.4 |
13.8 |
0.66 (0.42–1.0) |
|
Sex | 0.1 | ||||||
F | 386 | 27.2 | 30.3 | 26.9 | 15.0 | 1 | |
M |
296 |
26.7 |
26.7 |
23.3 |
23.3 |
1.2 (0.95–1.6) |
|
HIV status | 1.0 | ||||||
Negative | 141 | 26.2 | 30.5 | 23.4 | 19.9 | 1 | |
Positive |
288 |
26.4 |
28.1 |
27.8 |
17.7 |
1.0 (0.7–1.4) |
|
Area | 0.005 | ||||||
South, near Chilumba | 70 | 38.6 | 22.9 | 24.3 | 14.3 | 0.51 (0.31–0.84) | |
Middle, near Nyungwe | 89 | 20.2 | 22.5 | 30.3 | 27.0 | 1.2 (0.79–1.9) | |
Around Karonga | 119 | 25.2 | 34.5 | 21.9 | 18.5 | 0.73 (0.48–1.1) | |
Karonga central (urban) | 209 | 21.5 | 25.4 | 32.5 | 20.6 | 1 | |
Kaporo area | 84 | 35.7 | 34.5 | 15.5 | 14.3 | 0.46 (0.29–1.1) | |
Far north | 57 | 28.1 | 40.4 | 21.1 | 10.5 | 0.54 (0.32–0.9) | |
Outside district |
16 |
26.9 |
28.9 |
25.6 |
18.6 |
0.41 (0.61–1.1) |
|
Tuberculosis type | 0.6 | ||||||
Smear positive | 485 | 26.2 | 29.5 | 25.4 | 19.0 | 1 | |
Smear negative | 145 | 29.7 | 24.8 | 27.6 | 17.9 | 0.94 (0.68–1.3) | |
Extrapulmonary |
52 |
30.8 |
32.7 |
19.2 |
17.3 |
0.78 (0.47–1.3) |
|
Previous tuberculosis | 0.6 | ||||||
No | 628 | 27.4 | 28.8 | 25.8 | 18.0 | 1 | |
Yes |
47 |
27.7 |
25.5 |
21.3 |
25.5 |
1.2 (0.68–2.0) |
|
Isoniazid resistance | 0.2 | ||||||
No | 641 | 28.1 | 27.9 | 25.9 | 18.1 | 1 | |
Yes |
39 |
12.8 |
43.6 |
15.4 |
28.2 |
1.5 (0.84–2.6) |
|
Died† | 1.0 | ||||||
No | 382 | 26.7 | 28.3 | 25.1 | 19.9 | 1 | |
Yes | 155 | 25.8 | 29.0 | 26.5 | 18.7 | 1.0 (0.72–1.4) |
*Odds ratio from ordered logistic regression. This represents the summary relative odds of larger clusters compared with smaller clusters across the 4 groups. Odds ratios >1 imply that the odds of being in a larger cluster are greater than in the baseline group. CI, confidence interval.
†Outcome recorded for 632 patients; those who were lost or transferred while receiving treatment are excluded from this analysis.