Simple sputum test for confirmation of childhood tuberculosis

01/05/05

NB. Please note that if you are outside North America, the embargo for LANCET press material is 0001 hours UK Time 7 January 2005.

Results of a South African study in this week's issue of THE LANCET show how a diagnosis of tuberculosis in young children can be confirmed by a straightforward sputum test, rather than the conventional and invasive procedure of gastric lavage.

Diagnosis of tuberculosis is difficult in infants and young children and can be complicated by HIV infection. Heather Zar (School of Child and Adolescent Health, University of Cape Town, South Africa) and colleagues studied 250 children aged 1 month to 5 years who were admitted for suspected pulmonary tuberculosis in Cape Town. Sputum induction and gastric lavage were done on three consecutive days according to a standard procedure.

Samples from induced sputum and gastric lavage were positive in 87% and 65% of children, respectively. The yield from one sample from induced sputum was similar to that from three gastric lavages. In addition, almost half of all culture positive sputum samples were also smear positive, enabling rapid diagnosis and initiation of treatment. There was no difference in the reliability of diagnosis between HIV-positive and HIV-negative children. Sputum induction was useful even in young infants, with almost 40% of children with a positive sputum culture being less than one year of age.

Professor Zar comments: "In children with suspected pulmonary tuberculosis, sputum induction, not gastric lavage, should be the standard technique for microbiological diagnosis. One sample is sufficient, but if resources allow and if the child is in hospital, two or three specimens can increase microbiological yield…The important clinical usefulness of sputum induction for diagnosis of tuberculosis in this study raises possibilities for its use in primary care, and for diagnosis of other respiratory diseases in infants and young children."

In a Research Letter (p 150), Daniel Vargus and colleagues present a preliminary comparison of the string test--where the removal of swallowed string from the upper gastrointestinal tract induces sputum-- with conventional sputum induction for the diagnosis of tuberculosis in 228 HIV-infected patients. These patients were under investigation for tuberculosis and were either unable to produce an adequate specimen or they had a previous negative specimen. 52 HIV-positive controls had the same procedure. The use of the string test followed by sputum induction detected more cases of tuberculosis on culture of the specimens than did sputum induction alone, including the diagnosis of one patient with tuberculosis in a group of asymptomatic controls.

Alwyn Mwinga (Global AIDS Program, Centers for Disease Control and Prevention, Lusaka, Zambia) in an accompanying commentary (p 97) welcomes the advances of these two studies, but cautions that more straightforward diagnostic procedures are needed in resource-poor settings. She states: "The development of a simple affordable dipstick test in whole blood that can detect tuberculosis infection in the HIV-infected infant and child will greatly improve the ability of health-care staff to provide appropriate treatment and avoid the inappropriate use of antibiotics. This situation is not a pipe dream when we consider the available resources for tuberculosis and HIV research and the current efforts in developing new diagnostics for tuberculosis. The Foundation for Innovative New Diagnostics (FIND), an independent not-for-profit foundation launched in 2003 by the Special Programme for Research and Training in Tropical Disease with funding from the Gates Foundation, has chosen tuberculosis as its first target. Several innovative and rapid tests are being developed with the support of FIND. The development of improved tools for the diagnosis of tuberculosis is one of the research goals of the National Institutes of Health in the USA. Someone in the world is infected with the tuberculosis bacillus every second, and someone dies from tuberculosis every 15 seconds, one out of every three being a child. Somber statistics, but not irreversible with the combined effort of scientists, funding bodies, public-health practitioners, and national governments in the search for improved diagnostics and treatment for tuberculosis."

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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