Thai drug-resistant tuberculosis predictive scores

Boonsarngsuk V, Tansirichaiya K, Kiatboonsri S
Correspondence: Dr Viboon Boonsarngsuk, bss-vb@hotmail.com

ABSTRACT
Introduction This study aimed to determine the prevalence and risk factors of drug-resistant tuberculosis (TB), and to develop a diagnostic algorithm for newly-diagnosed TB patients.
Methods This is a retrospective medical chart review of 290 patients who were diagnosed with bacteriological-proven pulmonary TB between 2000 and 2006 in Ramathibodi Hospital, Thailand. Patient characteristics, radiological and microbiological findings, as well as a history of previous TB disease and treatment, were included in the analysis of predictive factors of drug resistance. Predictive scores were derived from statistically significant factors at the cut-off point of the receiver-operating curve that yielded the best area under the curve.
Results The resistance rate to each of these drugs among 290 patients was: isoniazid, 6.9 percent; rifampicin, 4.5 percent; either isoniazid or rifampicin, 9.0 percent; and multidrug resistance, 2.4 percent. Far advanced TB was an independent risk factor for isoniazid resistance. Rifampicin resistance was associated with recurrent TB within six months after the completion of treatment and prior incomplete TB treatment. A drug-resistant TB predictive score of either isoniazid or rifampicin resistance was developed based on the aforementioned factors. The cut-off score of greater than or equal to 3 yielded the least error of classification in differentiating patients with the resistant strain from those with the susceptible strain at a sensitivity of 57.7 percent, a specificity of 67.8 percent, a positive predictive value of 15 percent and a negative predictive value of 94.2 percent.
Conclusion Our study suggested a drug-resistant TB predictive score for the exclusion of either isoniazid or rifampicin resistance, and provides a decisional guide for the clinician on whether to send a patient’s respiratory specimen for sputum culture and drug susceptibility testing.

Keywords: drug-resistant tuberculosis, drug susceptibility testing, tuberculosis
Singapore Med J 2009; 50(4): 378-384