|EXAMINATION OF MULTIPLE SPUTUM SPECIMENS IN A TUBERCULOSIS
|P Chandrasekhar, SS Nair, K Padmanabha Rao, G Ramanatha
Rao & Pyare Lal: Tubercle, 1970, 51, 255-62.
Prevalence surveys are useful for estimating the
tuberculosis problem in different countries. Three techniques are
commonly used in surveys, tuberculin test, mass miniature radiography
and sputum examination. Each has its own limitations. A limitation
of sputum examination is that all the sputum positive cases in the
community cannot be diagnosed when only one sample of sputum is
examined from each eligible person. Multiple sputum examinations
are not often possible under field conditions of surveys covering
the whole community. It would be worthwhile to have some idea of
the extent of under-diagnosis in sputum examination. For this purpose,
during an epidemiological survey, four specimens of sputum were
collected within seven days of X-ray examination from each person
with an abnormal chest X-ray in 30 villages of a district of south
India. Each specimen was examined by Fluorescent Microscopy (FM),
Ziehl Neelson (ZN) technique and culture.
There were 34 culture positive cases among 2,164
persons for whom all the four culture examination results were available.
Of them, 21 (62%) were found positive on one specimen. The second
specimen increased the positivity to 32 (95%). Thus, for detecting
both smear and culture positive cases two specimens are adequate.
A third specimen is helpful for detecting cases positive by culture
alone. An estimate of prevalence obtained from one sputum specimen
can be estimated for the prevalence obtained from many specimens
by applying correction factor of 1.67 and estimates based on two
specimens by applying 1.26. Of the remaining 37 smear positive cases
detected by one specimen, 20 were smear positive and culture negative.
Of the remaining 17 smear positive and culture positive, 14(82%)
were detected by one smear examination only.
ZN positives not confirmed by culture (mostly with
less than four bacilli reported in the smear) increased from 7 from
the first specimen to 18 from all four specimens, while positives
confirmed by culture method showed only a marginal increase from
13 to 15. FM did not have this disadvantage as only two were culture
negative among the 18 smear positive results by FM method. Examination
of two specimens by FM detected about 95% of cases demonstrable
by this method. But with the ZN technique additional specimens may
add more false positives. Thus, for detecting cases
both smear and culture-positive two specimens appear adequate. A
third specimen is helpful for detecting cases positive on culture
|KEY WORDS: SPUTUM EXAMINATION, MULTIPLE SPUTUM
SPECIMEN, SURVEY, RURAL, ZIEHL NEELSON, FLUORESCENT, CULTURE.