Table 3

Broad-spectrum antibiotic use, epidemiological risk, reactivation risk and laboratory features in patients with pulmonary tuberculosis by smear status

Smear statusP value*
n (%)
n (%)
Assessed, n313151162
Antibiotic use†
 Yes12486 (56.9)38 (23.5)<0.001
 No18965 (43.1)124 (76.5)
Epidemiological risk‡
 Yes301144 (95.4)157 (96.9)0.48
 No127 (4.3)5 (3.1)
Reactivation risk§
 Yes239 (5.9)14 (8.6)0.35
 No290142 (94.1)148 (91.4)
Complete blood count¶
 Normal haemoglobin; leucocytosis**87 (4.6)1 (0.6)0.03
 Normal haemoglobin; normal/low leucocyte count13946 (30.4)93 (57.4)<0.001
 Anaemia and leucocytosis**3625 (16.5)11 (6.7)0.01
 Anaemia and normal/low leucocyte count13073 (48.5)57 (35.3)0 .01
Chest radiographs
 Typical appearance††176118 (78.1)58 (35.8)<0.001
 Bilateral‡‡11884 (55.6)34 (21.1)<0.001
 Cavitary10393 (61.5)10 (6.1)<0.001
 Extent: moderate to far-advanced disease§§159123 (81.4)36 (22.2)<0.001
  • *Difference in proportions [(smear-positive)−(smear-negative)]; sample size was adequate to detect observable differences.

  • †Refers to broad-spectrum antibiotic use in the 6 months preceding the date of diagnosis (the start date of treatment).

  • ‡Epidemiological risk for exposure to Mycobacterium tuberculosis.

  • §Moderate to high-risk factors for the reactivation of tuberculosis in those with latent tuberculosis (TB) infection, according to the Canadian Tuberculosis Standards.

  • ¶The reference range for a normal haemoglobin is 135–175 g/L and 120–160 g/L for males and females, respectively. The reference range for a normal leucocyte count is 4.0–11.0x109/L. Anaemia and leucocytosis among smear-positive cases as compared with smear-negative cases (65% vs 42% and 21% vs 7%) were significant at p≤0.05, using Pearson’s χ2 test.

  • **Fisher’s exact test and χ2 test used to test for differences.

  • ††Typical=upper lung zone predominant infiltrate, with or without cavitation, but no discernable adenopathy.

  • ‡‡Of the 176 cases without bilateral disease, 27 had a normal chest X-ray (CXR): 25 smear negative and 2 smear positive. One of the 25 smear-negative cases with a ‘normal’ CXR had evidence of intrathoracic adenopathy and normal-appearing lung parenchyma.

  • §§Includes three cases with a miliary pattern (see text).