Univariate analysis of factors that may associate with culture gain from supervised and induced sputum relative to two unsupervised specimens among the 78 patients with culture-proven pulmonary tuberculosis (TB)
| Predictor variables | No gain | Gain | OR (95% CI) | p-value |
| Patients n | 43 | 35 | ||
| Race | ||||
| Chinese | 93.0 | 88.6 | 1.7 (0.4–8.3) | 0.69 |
| Non-Chinese | 7.0 | 11.4 | ||
| Sex | ||||
| Male | 62.8 | 62.9 | 1.0 (0.4–2.5) | 1.00 |
| Female | 37.2 | 37.1 | ||
| Mean age after natural logarithmic transformation loge yrs | 3.63 (0.48) | 3.51 (0.47) | 0.6 (0.2–1.5) | 0.24 |
| Smoking status | ||||
| Nonsmoker | 46.5 | 60.0 | 0.6 (0.2–1.4) | 0.24 |
| Ever-smoker | 53.5 | 40.0 | ||
| Comorbidities predisposing to active TB | ||||
| No | 86.0 | 88.6 | 0.8 (0.2–3.1) | 1.00 |
| Yes | 14.0 | 11.4 | ||
| History of previous anti-TB treatment | ||||
| No | 86.0 | 94.3 | 0.4 (0.1–2.0) | 0.29 |
| Yes | 14.0 | 5.7 | ||
| Respiratory symptoms on presentation | ||||
| Yes | 81.4 | 57.1 | 3.3 (1.2–9.1) | 0.02# |
| No | 18.6 | 42.9 | ||
| Extent on chest radiography | ||||
| More than right upper lobe | 41.9 | 8.6 | 7.7 (2.0–29.4) | 0.002# |
| Less than right upper lobe | 58.1 | 91.4 | ||
| Cavitation on initial chest radiography | ||||
| Yes | 23.3 | 5.7 | 5.0 (1.0–24.4) | 0.07# |
| No | 76.7 | 94.3 | ||
| Ease of sputum expectoration | ||||
| No sputum or difficult | 55.8 | 62.9 | 0.7 (0.3–1.9) | 0.53 |
| Other | 44.2 | 37.1 |
Data are presented as %, unless otherwise stated. The first subgroup is the reference group for interpreting odds ratios. Natural logarithmic transformation was applied to normalise the distribution of age, which was positively skewed. OR: odds ratio; CI: confidence interval. #: factors with a p-value <0.2 were further analysed in a logistic risk model of sputum culture gain by including factors with a p-value <0.05 by default and selecting the rest by forward stepwise regression using p-values of 0.05 and 0.10 as cut-offs for entry and removal, respectively. Compared with counterparts, extent of disease less than right upper lobe and lack of respiratory symptoms on presentation were significantly associated with sputum culture gain, adjusted OR (95% CI) being 7.2 (1.9–28.0) and 3.0 (1.0–8.9), respectively. Thus, smear-negative patients with extent of disease less than right upper lobe or no respiratory symptoms were more likely to benefit from supervised expectoration and sputum induction.