New findings could make TB testing more accessible in poor countries

TDR news item
28 July 2011

Two newly published studies on alternative methods of testing for tuberculosis (TB) could lead to more efficient and accessible diagnostics in poor countries. Every year, nearly 9 million people develop TB and 1.7 million people die from TB worldwide. Mycobacterium tuberculosis, which causes TB, is spread in airborne droplets when people with the disease cough or sneeze, so it is essential to rapidly identify and treat individuals with suggestive symptoms to avoid the spread of infection.

The studies, which examined new methods of sputum smear collection, were conducted with 6627 patients who had had cough for more than two weeks (a characteristic symptom of TB) in Ethiopia, Nepal, Nigeria and Yemen. The studies, led by Luis E. Cuevas and Mohammed Yassin from the Liverpool School of Tropical Medicine and coordinated jointly with Andrew Ramsay at TDR, the Special Programme for Research and Training in Tropical Diseases, were recently published in PLoS Medicine.

Both studies demonstrate that simpler methods work just as well as traditional methods for diagnosis and could have important implications for the ways in which the diagnosis is done in poor countries.

The first study suggests that a sputum collection scheme in which two samples are collected one hour apart followed by a morning specimen could identify as many smear-positive patients as the standard “spot-morning-spot” scheme in which one sample is collected the first day and two samples the second day of consultation. As the first two sputum samples collected in one day identify the same number of patients with TB than samples collected over several days, this streamlined "same-day" or "frontloaded" scheme would be more convenient for the patients. It would help increase testing as the current cumbersome method requires return visits, which patients frequently skip. The conclusion of the investigators was that “the identification of the majority of smear-positive patients may require no more than one patient visit, and […] has the potential to improve the diagnosis of pulmonary TB in low- and middle-income countries. A single-visit diagnosis would represent a substantial opportunity to improve the delivery of TB services, particularly to the poor.”

The study data was considered by a team of experts advising the WHO and resulted in new guidelines on the "same-day" diagnosis of TB.

The second study shows that examining sputum with a new kind of microscope called a light emitting-diode fluorescence microscope (or LED-FM) is more sensitive and faster than examining sputum using traditional light microscopes, but that proper training is required to maintain the same level of accuracy. This study, which is a sub-study of the main trial, examined nearly 2400 patients to show that the LED-FM could identify more people with TB than the standard smear microscopy test. The authors concluded “this study has shown that LED -FM can play a key role in reaching the [World Health Organization] targets for TB detection, reducing laboratory workloads, and ensuring poor patients’ access to TB diagnosis and prompt treatment.” The data of this study was also submitted to WHO, and WHO has recently recommended that "conventional fluorescence microscopy be replaced by LED microscopy, and that LED microscopy be phased in as an alternative for conventional Ziehl-Neelsen light microscopy".

For more information, contact
Dr Luis E. Cuevas , or
Dr Andrew Ramsay