Evaluation of Diagnostic Properties of the Sputum Smear versus Culture Method for Tuberculosis in an Ecuadorian Urban Public Health Facility

The accurate diagnosis and effective prevention and control of tuberculosis (TB) are major global public health challenges. Ecuador has among the highest documented TB incidence (65/100,000 inhabitants) and mortality rates in the Americas region (27/100,000 inhabitants); TB multidrug resistance is also becoming increasing common. The culture method is the preferred method of choice for diagnosing TB in the United States and many other high resource countries due to its high documented sensitivity. An added benefit is that it also can be used to detect primary TB resistance. In contrast, despite its lower diagnostic sensitivity, the sputum smear method is most often used in low resource countries with a high disease burden, including Ecuador. The main reason for this is due to its lower cost, quick turnaround time and reduced technology requirements. However, scarce data have been published comparing the diagnostic properties of the two methods in a high-volume public health care setting in Ecuador or neighboring countries. The major objective of the present study was to compare the diagnostic properties of the sputum smear with the culture method including its sensitivity, specificity, and predictive value. Data were collected on a consecutive sample of 1687 suspected TB or primary resistance cases referred during a 12-month period (1999-2000) by public health care professionals to the Instituto Nacional de Higiene “Leopoldo Izquieta Perez” National Reference Laboratory in Quito, Ecuador. The study findings have important practical application for TB diagnosis in low resource, low technology public health settings with a high patient volume.