Table 2. A comparison of TB yield in smear/culture and Xpert® based algorithms and trends over time.
| TB yield | 95% CI | Risk difference (95% CI) | p-value | |
|---|---|---|---|---|
| All cases (simple model) | ||||
| Smear/culture-based algorithm | 20.9% | 19.9% to 22.0% | -3.0% (-4.3% to -1.7%) | <0.001 |
| Xpert-based algorithm | 17.9% | 16.4% to 19.5% | ||
| All cases adjusted for MDR-TB risk | ||||
| Smear/culture-based algorithm | 20.1% | 18.8% to 21.5% | -2.9% (16.4% to 19.5%) | <0.001 |
| Xpert-based algorithm | 17.2% | 15.4% to 19.0% | ||
| Amongst low MDR-TB risk cases (simple model) | ||||
| Smear/culture-based algorithm | 20.3% | 19.0% to 21.5% | -3.2% (-4.9% to -1.4%) | <0.001 |
| Xpert-based algorithm | 17.1% | 15.1% to 19.1% | ||
| Amongst high MDR-TB risk cases (simple model) | ||||
| Smear/culture-based algorithm | 24.4% | 23.2% to 25.6% | -2.3% (-3.8% to -0.7%) | 0.004 |
| Xpert-based algorithm | 22.1% | 21.0% to 23.3% | ||
| For cases in both the smear/culture and Xpert-based algorithms by time point (simple model) | ||||
| T1 (November 2010) | 23.6% | 22.2% to 25.1% | -0.9% (-1.2% to -0.6%)a | <0.001 |
| T2 (May 2011) | 20.4% | 19.1% to 21.8% | ||
| T3 (November 2011) | 19.4% | 18.3% to 20.5% | ||
| T4 (May 2012) | 17.4% | 15.8% to 19.1% | ||
| T5 (November 2012) | 19.5% | 17.8% to 21.2% | ||
| T6 (May 2013) | 16.6% | 15.0% to 18.2% | ||
| T7 (November 2013) | 17.5% | 15.0% to 20.0% | ||
| All cases adjusted for temporal trends | ||||
| Smear/culture-based algorithm | 19.1% | 17.6% to 20.5% | 0.3% (-1.8% to 2.3%) | 0.796 |
| Xpert-based algorithm | 19.3% | 17.7% to 20.9% | ||
The table shows TB yield comparisons between the smear/culture and Xpert-based algorithms and temporal trends in yield at time-points T1 to T7 in primary health sites in Cape Town. The outputs are from a binomial regression model, adjusted for clustering of presumptive TB cases at sites. In the simple model adjustments have not been made for differences in MDR-TB risk profiles between the algorithms or for temporal trends.
aThis is the mean risk difference per time point and 95% confidence interval.
Abbreviations: TB—tuberculosis, MDR-TB—multidrug-resistant tuberculosis, CI—confidence interval.