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| |  Study Establishes Most Effective Technique for Diagnosing Childhood Tuberculosis in Resource-Poor Countries NEW YORK -- July 26, 2010 -- A tuberculosis (TB) culture method called microscopic-observation drug-susceptibility (MODS), using 2 gastric aspirate specimens from each child tested, is significantly more sensitive and faster than conventional culture tests, diagnosing 70% more cases of pulmonary TB among children ages 12 years and under. This is the best available diagnostic test for confirming paediatric pulmonary tuberculosis in resource-poor settings, particularly in children with strong clinical evidence of TB, concludes an article published online first and in the August edition of The Lancet Infectious Diseases. The diagnosis of pulmonary TB is difficult in children because symptoms are nonspecific, respiratory specimens are difficult to obtain, and even in the best conditions Mycobacterium tuberculosis is confirmed in fewer than half of children with clinically diagnosed TB. In this study, Richard Oberhelman, Tulane School of Public Health, New Orleans, Louisiana, and international colleagues compared the accuracy of new diagnostic techniques for pulmonary tuberculosis in children in a resource-poor area. Two hundred eighteen children with suspected pulmonary TB cases were enrolled from 2 hospitals in Lima, Peru, between August 2002 and January 2007. The cases were grouped into moderate-risk and high-risk categories based on clinical evidence of TB, and age and sex matched with 238 healthy controls. Two specimens of nasopharyngeal aspirates, stool samples, and gastric aspirates were taken from each case and examined for M tuberculosis using MODS culture, standard Lowenstein-Jensen culture, and a heminested polymerase chain reaction (PCR) test. Of the children tested, 22 had culture-confirmed TB. M tuberculosis was isolated from gastric aspirate in all 22 cases compared with 4 cases from stool samples and 12 cases from nasopharyngeal aspirate. Importantly, adding a duplicate sample increased diagnostic yield by 37% -- the first gastric aspirate sample was culture positive in 16 (72.7%) of 22 patients and the second in 6 (27.3%) of 22 patients. MODS almost doubled the sensitivity of detecting TB compared with the conventional Lowenstein-Jensen method, diagnosing 20 (90.9%) of 22 patients compared with 13 (59.1%), and in less than half the time (10 vs 25 days). The authors noted that although PCR was not specific or sensitive enough for routine diagnosis, in high-risk children, gastric aspirate PCR rapidly identified half of all culture-positive cases, and could be useful as a screening test in these children. The researchers concluded, "Collection of duplicate gastric-aspirate specimens from high-risk children for MODS culture increased microbiological diagnosis of tuberculosis by more than a third … and was the best available diagnostic test for pulmonary tuberculosis." Stephen Graham, University of Melbourne, Melbourne, Australia, discussed the problems surrounding research into tuberculosis diagnosis in children and said, "The recognised difficulties with confirmation of diagnosis have contributed to a common, and perhaps erroneous, perception that the diagnosis of childhood tuberculosis is always difficult. Clinical diagnosis is fairly straightforward in many patients and this unnecessary negative perception can be a barrier to improving clinical management, supporting child tuberculosis research, and reporting of disease burden."
SOURCE: The Lancet Infectious Diseases
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