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Tuberculosis
Need for better diagnostics
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| Microscopy Center (peripheral laboratory
level), Ethiopia (photo: WHO)
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The mainstay for Tuberculosis (TB) diagnosis in disease endemic developing countries
is sputum smear microscopy developed in the 1880s and which has remained
essentially unchanged since then. Microscopy is an attractive technology
platform for public-health programs: it consists of one piece of
equipment (the microscope); can be used for more than one purpose;
provides visual evidence and in most instances is specific enough not to
require confirmatory testing.
However, the sensitivity of this technology is low: it can only detect
roughly half of all active cases of tuberculosis when properly used, and in
areas struck by the HIV epidemic, where co-infections are frequent, as well as
in children, the sensitivity is even lower. Moreover, though routinely described
as a simple technology, microscopy is actually complex, and highly dependent on
the training and diligence of the microscopist, requiring multiple examinations.
Furthermore, under programmatic conditions it may take days rather than hours to
complete, with the consequence that many patients drop out during the diagnostic
process.
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| Health Post (primary health care level), Lima,
Peru (photo: FIND) |
The lack of accurate, robust, and rapid diagnostics impedes tuberculosis
patient management and disease control. For communities, the risk of
transmission from undetected cases requires widespread access to diagnostic
services and early detection. Unfortunately, diagnostic services in most places
where tuberculosis is endemic fail both the individual and the community.
Patients are often diagnosed after weeks to months of waiting, at substantial
cost to themselves, and at huge cost to society. Many patients are never
diagnosed and contribute to the astonishing number of yearly deaths from
tuberculosis worldwide.
More than one type of test is needed for the different levels of the health
care system: a point-of-care test for use at primary health
care level (health post) where the majority of patients seek medical attention
but where diagnosis is currently based on clinical signs and symptoms only; at
the peripheral laboratory level or the health center or district hospital, an
alternative to microscopy, with a simpler technology that can detect both the
smear-positive and smear-negative tuberculosis; and at the district and national
reference laboratory level, faster substitutes to culture for detecting
smear-negative tuberculosis, improved antibiotic susceptibility testing, and
tests for the detection of latent infection.
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| Referral laboratory (national reference
laboratory level), Ho Chi Minh City, Vietnam (photo:
FIND) |
FIND is prioritizing tests that can be adopted at the lowest level of the
health system, where a large number of patients first seek care. The
technologies targeted for each level are intended to match the human resources
available and the degree of complexity of the diagnostic question.
Some of the diagnostic tools expected to be introduced into control programs
will be incremental improvements on existing technologies while others will be
radically new. The speed and extent of adoption of new technologies will depend
on the balance between the benefits they bring and the degree of disruption
their implementation causes. For instance, a simplified microscopy method may
see greater adoption than a novel alternative that necessitates changes in the
way testing or case notification are carried out. On the other hand, a new
method that rapidly identifies all smear-positive and many smear-negative cases
might, if suitably robust and specific, see widespread use and could
substantially replace microscopy.
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