Table 2—

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 variablesNo gainGainOR (95% CI)p-value
Patients n4335
 Chinese93.088.61.7 (0.4–8.3)0.69
 Male62.862.91.0 (0.4–2.5)1.00
Mean age after natural logarithmic transformation loge yrs3.63 (0.48)3.51 (0.47)0.6 (0.2–1.5)0.24
Smoking status
 Nonsmoker46.560.00.6 (0.2–1.4)0.24
Comorbidities predisposing to active TB
 No86.088.60.8 (0.2–3.1)1.00
History of previous anti-TB treatment
 No86.094.30.4 (0.1–2.0)0.29
Respiratory symptoms on presentation
 Yes81.457.13.3 (1.2–9.1)0.02#
Extent on chest radiography
 More than right upper lobe41.98.67.7 (2.0–29.4)0.002#
 Less than right upper lobe58.191.4
Cavitation on initial chest radiography
 Yes23.35.75.0 (1.0–24.4)0.07#
Ease of sputum expectoration
 No sputum or difficult55.862.90.7 (0.3–1.9)0.53
  • 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.