Chest Radiographic Patterns and the Transmission of Tuberculosis: Implications for Automated Systems.
Computer-aided detection to identify and diagnose pulmonary tuberculosis is being explored. While both cavitation on chest radiograph and smear-positivity on microscopy are independent risk factors for the infectiousness of pulmonary tuberculosis it is unknown which radiographic pattern, were it detectable, would provide the greatest public health benefit; i.e. reduced transmission. Herein we provide that evidence.



1) to determine whether pulmonary tuberculosis in a high income, low incidence country is more likely to present with "typical" adult-type pulmonary tuberculosis radiographic features and 2) to determine whether those with "typical" radiographic features are more likely than those without such features to transmit the organism and/or cause secondary cases.



Over a three-year period beginning January 1, 2006 consecutive adults with smear-positive pulmonary tuberculosis in the Province of Alberta, Canada, were identified and their pre-treatment radiographs scored by three independent readers as "typical" (having an upper lung zone predominant infiltrate, with or without cavitation but no discernable adenopathy) or "atypical" (all others). Each patient's pre-treatment bacillary burden was carefully documented and, during a 30-month transmission window, each patient's transmission events were recorded. Mycobacteriology, radiology and transmission were compared in those with "typical" versus "atypical" radiographs.



A total of 97 smear-positive pulmonary tuberculosis cases were identified, 69 (71.1%) with and 28 (28.9%) without "typical" chest radiographs. "Typical" cases were more likely to have high bacillary burdens and cavitation (Odds Ratios and 95% Confidence Intervals: 2.75 [1.04-7.31] and 9.10 [2.51-32.94], respectively). Typical cases were also responsible for most transmission events-78% of tuberculin skin test conversions (p<0.002) and 95% of secondary cases in reported close contacts (p<0.01); 94% of secondary cases in "unreported" contacts (p<0.02).



As a group, smear-positive pulmonary tuberculosis patients with typical radiographic features constitute the greatest public health risk. This may have implications for automated detection systems.
Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
Angela
A
Lau
Department of Radiology, University of Alberta, Edmonton, Alberta, Canada.
James
J
Barrie
Department of Radiology, University of Alberta, Edmonton, Alberta, Canada.
Christopher
C
Winter
Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
Abdel-Halim
AH
Elamy
Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Alberta, Canada.|Provincial Laboratory for Public Health, Alberta Health Services, Edmonton and Calgary, Alberta, Canada.
Gregory
G
Tyrrell
Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.|School of Public Health, University of Alberta, Edmonton, Alberta, Canada.
Richard
R
Long
D000293:Adolescent; D000328:Adult; D000368:Aged; D001331:Automation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013902:Radiography, Thoracic; D014397:Tuberculosis, Pulmonary / Q000000981:diagnostic imaging / Q000635:transmission*; D055815:Young Adult