Table 3.
Procedures and results of robust Poisson regression analysis of the association between early sputum culture conversion and pyrazinamide use with susceptibilitya
| Factor | Change in coefficient of Z use with susceptibility (%) | Reason for exclusion from multivariable analysis | Adjusted risk ratio (95% CI) |
|---|---|---|---|
| Adverse social factor | −4.9 | <10% change in coefficient | |
| Use of thioamide | −5.5 | <10% change in coefficient | |
| Use of ethambutolb | −10.4 | 1.08 (0.89–1.30) | |
| Use of cycloserine | −42.6 | Multicollinearity | |
| Use of PASb | −15.8 | 1.02 (0.84–1.24) | |
| Use of <4 drugs with activity in vitro | −39.3 | Multicollinearity | |
| Susceptible to ofloxacinb | −44.8 | 1.68 (1.08–2.62) | |
| Susceptible to SLIDs | −27.3 | Multicollinearity | |
| Susceptible to ethionamideb | −25.1 | 1.35 (0.84–2.16) | |
| Susceptible to ethambutol | −13.1 | Multicollinearity | |
| Susceptible to cycloserine | 3.3 | <10% change in coefficient | |
| Z use with susceptibilityb,c | Reference | ||
| Z use with resistance (subgroup B) | 0.727 (0.469–1.127)d | ||
| Z nonuse with susceptibility (subgroup C) | 1.008 (0.823–1.234)e | ||
| Z nonuse with resistance (subgroup D) | 0.914 (0.703–1.190)f |
See footnote a of Table 2 for definitions of abbreviations.
These five factors were included in robust Poisson regression analysis to estimate the adjusted risk ratios of early sputum culture conversion in the presence of pyrazinamide use with susceptibility in comparison with each of the other alternatives.
In univariate analysis, this factor was evaluated as a binary variable comprising pyrazinamide use with susceptibility as the reference subgroup versus the others. After identifying potential factors that may confound the association between this factor and early sputum culture conversion, “others” was expanded into three subgroups, namely, pyrazinamide use with resistance, pyrazinamide nonuse with susceptibility, and pyrazinamide nonuse with resistance.
Taking subgroup B (pyrazinamide use with resistance) as the reference group, the adjusted risk ratio becomes 1.38 (95% CI, 0.89 to 2.12), which is the reciprocal of 0.727 (95% CI, 0.469 to 1.127).
Taking subgroup C (pyrazinamide nonuse with susceptibility) as the reference group, the adjusted risk ratio becomes 0.99 (95% CI, 0.81 to 1.22), which is the reciprocal of 1.008 (95% CI, 0.823 to 1.234).
Taking subgroup D (pyrazinamide nonuse with resistance) as the reference group, the adjusted risk ratio becomes 1.09 (95% CI, 0.84 to 1.42), which is the reciprocal of 0.914 (95% CI, 0.703 to 1.190).