|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.
|THE USE OF SCREENING TOOLS FOR THE ESTIMATION OF
TUBERCULOSIS CASE RATES IN A COMMUNITY
|AK Chakraborty: Indian J Public Health 1980, 24,
The problem in using simple tools e.g. chest symptoms
for epidemiological surveys, designed to quantify the problem is
that estimates from these simple surveys are considerable underestimates.
Recent research has, however, paved the way for the use of these
simpler tools for use in estimating tuberculosis case prevalence
rates in the community. A tool which is simple, convenient to use
and maintain, cheap but highly sensitive is called "screening
tool". Such tools are used for making initial selection of
the given population. Tuberculin test, X-ray & symptom elicitation
are the main screening tools used for epidemiological surveys and
TB Control Programme. In the programme, symptom elicitation and
X-ray examination are the screening tools of choice for Case-finding.
In the survey, tuberculin and X-ray are the only two tools used,
although tuberculin is not a good screening tool (40% population
infected). Use of symptom screening in surveys, however, is restricted
in the absence of adequate information on comparison of prevalence
rates obtained by this method of screening with the best estimate.
The performance of symptom screening with either culture or smear
microscopy have been attempted. They showed that by applying suitable
correction factors they may be rendered comparable to the best estimate.
The symptoms may be useful in the survey as a screening tool and
may give the rates as proximate to the true rates as possible. They
will enable considerable simplification of epidemiological studies
in tuberculosis without compromising on the precision of the estimates
|KEY WORDS: SCREENING TOOLS, ESTIMATES, CASE
RATE, SYMPTOMS, X-RAY, TUBERCULIN, SURVEY.