|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.
|ESTIMATION OF NUMBER OF REPEAT EXAMINATIONS REQUIRED
TO DETECT ALL TB CASES IN THE COMMUNITY
|R Rajalakshmi & SS Nair: Indian J Public Health
1976, 20, 118-21.
Examination of only one sputum sample cannot detect
all the sputum positive cases in the community. To obtain better
estimates of the prevalence of bacteriologically confirmed disease
in the community, a study was conducted to find out the additional
yield of cases through collection and examination of eight sputum
specimens and also in order to work out correction factors for
estimates based on one or two sputum samples, as collecting multiple
sputa is very difficult. The study was carried out in 77 villages
in Nelamangala Taluk of Bangalore. In all, 5826 persons were referred
for sputum examinations.
Results of all the eight culture examinations were
available for 2973 (51% of the eligibles). Of these 64 persons were
positive by culture of atleast one specimen. Each of the eight specimens
has the chance of detecting a case and any one of them could be
considered as first or second specimen etc. To overcome this difficulty
80 permutations were randomly chosen out of the total 40,320 permutations
possible. Cases from first specimen and additional cases from subsequent
specimens were calculated through four mathematical equations. The
first equation namely Y = KXm (28.66 x-1.40) has been considered
as providing the best fit to the observed data. On the basis of
this equation it appears that additional positives could be obtained
upto the 1Oth specimen. Out of 64 culture positive cases, only 72%
of positives could be detected by first two samples. To get about
95% of the cases, it is necessary to examine at least six specimens
from each individual. Multiple samples are rewarding for detecting
even high grade cultures.
|KEY WORDS: MULTIPLE SPUTUM SPECIMEN, SPUTUM
EXAMINATION, CASE YIELD, PREVALENCE, CASE, SURVEY.
|PRECISION OF ESTIMATES OF PREVALENCE OF BACTERIOLOGICALLY
CONFIRMED PULMONARY TUBERCULOSIS IN GENERAL POPULATION
|SS Nair, GD Gothi, N Naganathan, K Padmanabha Rao,
GC Banerjee & R Rajalakshmi: Indian J TB 1976, 23, 152-59.
This paper reports on a study conducted in the
year 1975 to estimate yield of tuberculosis cases from multiple
sputum specimens, and work out correction factors to be applied
to estimates based on small number of specimens. Eight sputum specimens
were collected within a fortnight from each person with an abnormal
chest X-ray during an epidemiological survey in 77 villages in a
district of south India. Each specimen was examined by Ziehl-Neelsen
technique of microscopy and culture. In all, 3,199 persons were
referred for sputum examination and results of all the eight specimens
were available for 1,652. Of the latter, 64 were culture positive.
The first specimen detected 58% of the culture
positives and the additional positives by later specimens generally
decreased. The contribution from the first specimen was 71% for
cultures showing good growth and 19% for cultures with scanty growth.
Similarly for positives on both culture and microscopy, first specimen
detected 87% whereas the corresponding proportion was 32% for those
positive only on culture. The type of specimen (viz., spot or overnight)
and age or sex of the case did not influence the yield from multiple
examinations. The precision of an estimate of prevalence will depend
on the number of specimens on which it is based and the coverage
obtained in the collection and examination of specimens. Correction
factors to be applied to such estimates based on one or two specimens,
for various levels of coverage have been presented. For example,
an estimate of prevalence based on one sputum specimen with 90%
coverage will have to be nearly doubled to get a more precise estimate.
Using these correction factors, revised estimates of prevalence
have been presented for a number of prevalence surveys conducted
in India. It has been estimated that the total number of infectious
cases in India at present may be at least 3 million, as against
2 million according to earlier estimates.
|KEY WORDS: PREVALENCE, CASE, RURAL POPULATION,
MULTIPLE SPUTUM SPECIMEN, ESTIMATES, SPUTUM EXAMINATION.