toman's tuberculosis case detection, treatment and monitoring

TOMAN’S TUBERCULOSIS
between populations (high- versus low-prevalence countries, early or late case presentation)
and details of the techniques used (e.g. fluorescence microscopy, concentration
techniques). Some, however, must be due to deficiencies in the execution of
the tests.
Despite the higher sensitivity of culture, use of the technique may not be particularly
rewarding for the examination of persons presenting spontaneously with chest
symptoms. In high-prevalence countries, with or without HIV being present, and
given correct use of both methods, the gain by culture over microscopy is estimated
to be about 25% (12). In low-prevalence countries, this gain will be greater, possibly
doubling the proportion of patients with positive bacteriological findings. Moreover,
culture has the added advantage of allowing identification of the mycobacterial
species, which is not possible with microscopy.
Thus, from the bacteriological point of view, two main categories of patient may
be distinguished: one much more infectious, discharging large numbers of tubercle
bacilli in almost every sputum specimen and easily detectable by microscopy, and the
other much less infectious, discharging smaller numbers of bacilli, usually not found
except by culture. As mentioned earlier, patients in the latter category may discharge
bacilli only intermittently (see “What is the additional yield from repeated sputum
examinations by smear microscopy and culture?”, page 46). Obviously, these two categories
also differ significantly in clinical and epidemiological respects.
Sputum status and clinical prognosis
The prognosis for patients with pulmonary lesions discharging small numbers of
bacilli, demonstrable only by culture, is generally more favourable prognosis than that
for smear-positive patients. In southern India, where an epidemiological survey had
been repeated at intervals, the fate of newly discovered cases was analysed (13, 14). Of
patients who had been smear-negative (two specimens) but positive by culture at the
time of detection of their disease, more than half were classified as cured (i.e. negative
by both smear and culture) within 18 months and about two-thirds within 3 years.
Moreover, the excess death rate was about one-third of that for smear-positive cases.
Thus, even under the living conditions of a very poor rural population, and without
treatment, the prognosis for smear-negative, culture-positive patients was relatively
favourable.
Though smear-negative cases were known to have a lower mortality, they were
thought to be at an early stage of the disease and it was assumed that they would deteriorate
further and become smear-positive later on. To prevent this, it was often considered
important to detect patients “early”, i.e. at a stage where the extent of the
disease is minimal and the lesion(s) are likely to contain a small number of bacilli
demonstrable only by culture. It has also been assumed that these patients rarely
have symptoms and thus may be detected best by indiscriminate mass radiography.
Surprisingly, this hypothesis has not withstood the test of time.
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