Evaluation of Clinical Parameters to Predict Mycobacterium tuberculosis in Inpatients

Derived a clinical prediction rule for the need for respiratory isolation of patients with suspected TB.

  • Authors
  • Claudia Henschke
  • Jennifer Kaplan
  • Juan P. Wisnivesky
  • Ronald G. Crystal
  • Thomas McGinn
  • Published
  • Arch Intern Med



Respiratory isolation has been recommended for all patients with suspected tuberculosis (TB) to avoid transmission to other patients and health care personnel. In implementing these guidelines, patients with and without TB are frequently isolated, significantly increasing hospital costs. The objective of this study was to derive a clinical rule to predict the need for respiratory isolation of patients with suspected TB.


To identify potential predictors of the need for isolation, 56 inpatients with sputum cultures positive for TB were retrospectively compared with 56 controls who were isolated on admission to the hospital based on clinically suspected TB but whose sputum cultures tested negative for TB. Variables analyzed included TB risk factors, clinical symptoms, and findings from physical examination and chest radiography.


Multivariate analysis revealed that the following factors were significantly associated with a culture positive for TB: presence of TB risk factors or symptoms (odds ratio [OR], 7.9 [95% confidence interval (CI), 4.4-24.2]), a positive purified protein derivative tuberculin test result (OR, 13.2 [95% CI, 4.4-40.7]), high temperature (OR, 2.8 [95% CI, 1.1-8.3]), and upper-lobe disease on chest radiograph (OR, 14.6 [95% CI, 3.7-57.5]). Shortness of breath (OR, 0.2 [95% CI, 0.12-0.53]) and crackles noted during the physical examination (OR, 0.29 [95% CI, 0.15-0.57]) were negative predictors of TB. A scoring system was developed using these variables. A patient’s total score of 1 or higher indicated the need for respiratory isolation, accurately predicting a culture positive for TB (98% sensitivity [95% CI, 95%-100%]; 46% specificity [95% CI, 33%-59%]).


Among inpatients with suspected active pulmonary TB, a prediction rule based on clinical and chest radiographic findings accurately identified patients requiring respiratory isolation.

PREVENTING THE spread of tuberculosis (TB) within hospitals is a major concern, particularly since the resurgence of TB in the mid-1980s15 and recent reports68 of nosocomial outbreaks of multidrug-resistant TB. The current guidelines9 for controlling the transmission of TB within institutions emphasize early identification of patients considered at high risk for the disease. The conventional strategy to deal with this problem is to isolate potentially contagious patients until 2 to 3 smears of sputum are negative for acid-fast bacilli (AFB). The sensitivity of the AFB smear, however, is not high,1014 and transmission of TB from patients with smears negative for AFB has been reported.15 Delayed recognition and isolation of patients with TB is a well-documented problem. For example, 3 studies1618 reported that in as many as 50% of the patients with a final diagnosis of TB the risk of the disease was not suspected and the appropriate infection control measures were not instituted on admission to the hospital. Conversely, Scott et al19 reported that in their institution, 92 patients without TB were isolated for every patient with TB, leading to a significant increase in hospital costs.

Both the underdiagnosis and overdiagnosis of patients at risk for TB make present isolation guidelines difficult to implement and not fully effective.19,20 In this context, it would be useful to develop predictive guidelines to more precisely identify patients at high risk for TB who require respiratory isolation on admission to the hospital. To identify early predictors of the need for respiratory isolation, the present study was designed to compare the clinical parameters of patients whose sputum cultures were positive for TB with individuals who were isolated on admission because of suspected disease but whose sputum cultures tested negative for TB.