Simple, non-invasive test for TB
A simple sputum test in infants and young children may result in a higher
rate of TB diagnosis than gastric lavage, the conventional and invasive
procedure, this according to the results of a South African study published in a
recent issue of The Lancet.
The study also found much higher rates of smear-positive tuberculosis in
young children than expected, challenging the notion that young children with TB
pose a low risk of infection to others.
Diagnosis of tuberculosis is difficult in infants and young children and can
be complicated by HIV infection. Gastric lavage requires the insertion of a tube
through the nose and throat into the stomach after an overnight fast, usually
after admission to hospital. This is followed by the introduction of saline
solution into the stomach in order to gather a sample of fluid from the stomach
that might contain TB bacteria. The procedure is distressing for both the child
and the health care worker and must be carried out on three consecutive days
according to current treatment guidelines.
Sputum induction in this study required gathering a sample of mucus that had
been coughed up after administration of saline solution to the lungs through a
nebuliser (a device which delivers a liquid into the lungs as tiny droplets).
This procedure is much less uncomfortable, requires a three-hour fast only, and
can be easily carried out on an outpatient basis.
Professor Heather Zar of UCT's School of Child and Adolescent Health and her
colleagues studied 250 children, aged one month to five 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. This represents a 5.6% difference in yield. 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 old.
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."
However, sputum induction requires a moderate level of technical facilities
that may not be available in all health care settings. Researchers in Peru have
investigated whether it is possible to obtain samples from the upper
gastrointestinal tract to improve TB diagnosis.
They taped one end of the string to the inside of the patient's cheek, and
then asked the patient to swallow a capsule containing the string. After four
hours the string was withdrawn, washed in saline and centrifuged to obtain the
sample.
In an accompanying editorial, Alwyn Mwinga of the US Centres for Disease
Control Global Aids Programme in Zambia says that while these development are
welcome, the ultimate aim must be a simple blood test for TB, using a dipstick
technology that can be used by any health care worker in any health care
setting.
More information:
Article courtesy UCT Monday Paper
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