|THE USE OF MATHEMATICAL MODELS IN THE STUDY OF EPIDEMIOLOGY
|HT Waaler, Anton Geser & S Andersen: Ame J Public
Health 1962, 52, 1002-13.
The paper has illustrated the use of mathematical
model (epidemetric model) for the prediction of the trend of tuberculosis
in a given situation with or without the influence of specific tuberculosis
control programme. The paper also advocates the use of models for
evolving applicable control measures by reflecting their interference
in the natural trend of tuberculosis in control areas. These models
were constructed by applying methods which have been developed and
utilised in other social sciences.
The precise estimates of the various parameters entering the model
must be available if realistic long term results are to be achieved
through model methodology. The need for exact data regarding prevalence
and incidence of infection and disease, necessitates longitudinal
surveys in large random population groups. It is, however, the present
authors firm opinion that it would be fruitful for almost any health
department, to compare their best available epidemiological knowledge
in a system of relationships in order to quantify their concept
of the situation. Such an exercise in mathematics would, in any
case, serve to sharpen the epidemiologists thinking and would lead
them to appreciate what data they need most urgently. The model
may help in predicting the trend of tuberculosis in a given situation.
|KEY WORDS: EPIDEMETRIC MODEL, SURVEY, TREND,
|SOME ASPECTS OF A TB PREVALENCE SURVEY IN A SOUTH
|Raj Narain, A Geser, MV Jambunathan & M Subramanian:
Bull WHO 1963, 29, 641-64 & Indian J TB 1963, 9, 85-116.
The objective was to establish the prevalence rates
for tuberculosis infection, radiologically active pulmonary tuberculosis
and bacteriologically confirmed diseases for different age and sex
groups. Tumkur District in Mysore State consisting of 2,392 villages,
10 towns of was selected for the study. The district headquarter
town Tumkur was excluded from the survey. Random sample of 62 villages
and 4 town blocks having a population of 34,746 persons constituted
the study population. All the individuals available in the registered
population were given a Mantoux test with 1 TU RT 23 with Tween
80. Longitudinal diameter of induration was read 3-4 days after
the test. At the time of tuberculin test, all persons aged 10 years
and above were offered a single 70mm photofluorogram. For each picture
read as abnormal, a spot specimen of sputum of the individual concerned
was collected at the time of reading the tuberculin test. Age and
sex distribution of infection and disease were studied.
Various parameters concerning the prevalence of
infection and disease in the community were reported. Prevalence
rate of infection in all ages and both sexes of the population was
found to be 38.3%, radiologically active tuberculosis 1.86% and
0.41% sputum positive disease. The infection and disease increased
with age; of the total diseased, half were in age group 40 years
and more and about 2/3 among males.
|KEY WORDS: SURVEY, PREVALENCE, INFECTION, DISEASE,
CASE, COMMIUNITY, RURAL, URBAN.
|A COMPARISON OF THE RELATIVE VALUE OF SINGLE AND
DOUBLE PICTURE TECHNIQUES IN TB PREVALANCE SURVEYS
|Raj Narain, SS Nair & P Chandrasekhar: Indian
J TB 1964, 11, 145-53.
Limitations of a single X-ray picture for locating
and interpreting shadows in the chest had been studied earlier.
In order to reduce these limitations, it was suggested that two
pictures of each person be taken where the second picture was to
be taken after a vertical displacement of X-ray tube, up or down
by about 4 to 5cms. The advantages of taking two pictures simultaneously
as compared to a single picture have not been studied so far. Two
mobile X-ray units each with an odelca camera were alternated for
the single and double picture examinations. A total of about 2,000
persons were X-rayed and were read independently by 3 readers. A
spot sample of sputum was collected 3-4 days later from persons
with abnormal X-ray shadows and was examined by direct smear microscopy.
Comparison of the readings of the two sets of pictures
did not show a better agreement between different (inter-
individual) readers or between two different readings of the same
reader (intra-individual) when the two picture technique was used.
The X-ray cases detected by double picture only by any one reader
were not confirmed, more often than those detected by single picture
only. The X-ray pictures of the bacillary cases were also not interpreted
more often as active tuberculosis by the two picture technique.
It was concluded that the double picture technique does not offer
any advantage over the single picture technique.
|KEY WORDS: SURVEY, PREVALENCE, X-RAY READING,
X-RAY FILM, SINGLE PICTURE, DOUBLE PICTURE.
|PROBLEMS IN DEFINING A CASE OF PULMONARY
TUBERCULOSIS IN PREVALENCE SURVEYS
|Raj Narain, SS Nair, K Naganna, P Chandrasekhar, G
Ramanatha Rao & Pyare Lal: Bull WHO 1968, 39, 701-29.
Generally there is no acceptable definition of
the term case of pulmonary tuberculosis, although such
a definition is of fundamental importance both in clinical medicine
where results of various chemotherapeutic regimens are compared,
as well as for the comparison of different epidemiological data.
The main purpose of this paper is to focus attention on the difficulties
of defining a case on the basis of bacteriological examination,
X-ray examination and tuberculin test. Data from two successive
prevalence surveys in a random sample of 134 villages in Bangalore
district with a population 70,000 have been utilized to illustrate
some of the difficulties in defining a case of pulmonary
tuberculosis for reporting the prevalence or incidence of the diseases.
The entire population was tuberculin tested with 1 TU RT 23 with
Tween 80 at both rounds and those 5 years of age and older were
examined by 70mm photofluorogram. The sputum specimens (spot and
overnight) were collected from those with any abnormality on X-ray
as recorded by either of the two independent readers. Both the specimens
were examined by fluorescent microscopy and Ziehl-Neelsen technique
and by culture.
Analysis of data has shown that the term a
case of pulmonary tuberculosis does not represent a single
uniform entity, but embraces cases of several types, differing considerably
in their tuberculin sensitivity, results of X-ray and sputum examination,
in the reliability of their diagnosis and mortality experience.
The status of cases found at initial and subsequent surveys showed
changes with time, and such changes show considerable differences
for the various types of cases. It was felt that a single straight-forward
definition of a case was not possible to suit all situations. One
has to use more than one definition. Although theoretically, finding
a single bacillus in sputum should be adequate proof of pulmonary
tuberculosis, it was shown that finding of a few bacilli (3 or less)
was very often due to artifacts and should not be the basis for
a diagnosis. It has also been found that positive radiological findings,
in the absence of bacteriological confirmation, indicate only a
high risk of the disease and not necessarily pulmonary tuberculosis.
Direct microscopy appears to be a consistent index of disease but
in community surveys has the limitation of missing a substantial
proportion of cases and of adding some false ones.
In view of the difficulty of providing a single
definition of a case of tuberculosis, four indices have been suggested.
(1) Cases definitely positive by direct smear; (2) Cases definitely
positive by culture; (3) All cases positive by culture (including
less than twenty colonies); (4) Sputum positive cases which are
radiologically active. Each of these could be used for different
situations. However, it was concluded that, there seems to be no
option but to use more than one definition for assessing the prevalence
and incidence of disease.
|KEY WORDS: CASE-DEFINITION, SURVEY, PREVALENCE,
|RESISTANT AND SENSITIVE STRAINS OF MYCOBACTERIUM
TUBERCULOSIS FOUND IN REPEATED SURVEYS AMONG A SOUTH INDIAN RURAL
|Raj Narain, P Chandrasekhar, RA Satyanarayanachar &
Pyare Lal: Bull WHO 1968, 39, 681-99.
The degree of the risk of infection and disease
in man from drug resistant strains of mycobacterium tuberculosis
is not clear. An increase in the prevalence of primary resistance
indicates the extent of such risk while an increase of secondary
or acquired resistance could be considered as a problem of
the individual patient and may reflect limitations of his treatment.
The present report describes the prevalence of
strains with acquired or primary resistance or of sensitive strains
found in 3 successive surveys in a sizable random sample of village
in a south Indian district. Changes in the status of cases with
such strains from one survey to another and their infectivity among
household contacts are also described. The prevalence of tuberculosis
infection among household contacts of cases with acquired resistance
to isoniazid was significantly higher than those with primary resistance
or with sensitive culture. This was probably due to the longer duration
of sputum positivity of isoniazid resistant strains at the time
of diagnosis. But infectivity as judged by the incidence of new
infection among household contacts was generally less for cases
with acquired or primary resistance than for cases with sensitive
cultures, though the difference observed was not statistically significant.
A large number of culture positive cases especially those with primary
resistance had no radiological evidence of active pulmonary tuberculosis.
The prevalence of primary resistance was high in certain categories
of cases and the differences between cases with primary resistance
and those with acquired resistance were many and large. It was suggested
that this could be due to the primary resistant cultures being those
of atypical mycobacteria, despite positivity in the niacin test.
There was a significant increase in the number of cases with acquired
resistance to isoniazid at the third survey owing to the irregular
treatment and supply of INH alone after the second round. The prevalence
of primary resistance at the three rounds was almost the same.
|KEY WORDS: DRUG RESISTANCE, M.TUBERCULOSIS,
RURAL POPULATION, INFECTIVITY, SURVEY.
|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.
|DISTRIBUTION OF TUBERCULOUS INFECTION AND DISEASE
IN CLUSTERS OF RURAL HOUSEHOLDS
|SS Nair, G Ramanatha Rao & P Chandrasekhar: Indian
J TB 1971, 18, 3-9.
Data from 62 randomly selected villages in a district
of south India, which formed part of a prevalence survey carried
out by the National Tuberculosis Institute, Bangalore, during 1960-61,
has been made use of. The survey covered 29,813 persons in 5,266
households. There were 70 cases with bacilli demonstrable either
in smear or culture and 300 suspect cases. Using the village map
(prepared by survey staff), case clusters were formed
first, with each case household as nucleus and adjacent households
within a maximum distance of about 20 meters on either side of the
case households. Households closest to the nucleus household on
either side have been called as 1st neighbourhood and those coming
next in proximity on either side as a 2nd neighbourhood and so on.
The case household and its four neighbourhood together was called
a cluster. If another case household was found within 4th neighbourhood
of the first case the cluster was extended by including the 4th
neighbourhood of the new case also. Such clusters were called composite
case clusters and clusters with only one case household as simple
case clusters. Similarly, suspect case clusters were formed and
differentiated as simple suspect clusters or composite suspect clusters.
Further, to serve as a control group, non-case clusters were constituted
from a systematic sample of 10% households that were not included
in case or suspect case clusters.
Out of 60 case clusters formed, only 7 have multiple
cases showing that there was no evidence of high concentration of
disease in case clusters. While the percentage of child contacts
(0-14 years) infected was considerably higher in case clusters (25.8%),
there was not much difference between suspect case clusters (14.9%)
and non-case clusters (9.8%). Similarly, there was not much difference
between simple and composite clusters. Infection among child contacts
was higher in case households as compared to their neighbourhoods.
To get some idea of the zone of influence of a case or suspect case,
prevalence of infection was studied for 10 neighbourhoods, in simple
clusters to avoid the influence of multiple cases. It appeared that
the zone of influence of a case may extend at least upto the 10th
neighbourhood. It was also noted that there was very little difference
between zones of influence of suspect cases and non-cases. Case
clusters in which the nucleus case had shown activity of lung lesion
(evident on X-ray reading) or had cough showed significantly higher
infection among child contacts. Clusters around cases positive on
both smear and culture did not show higher infection than those
around cases positive on culture only. (This may be due to sputum
examination of single specimen only).
Out of the total infected persons in the community,
only 2% were in case households and 7% in suspect case households,
over 90% being in non-case households. The zone of influence of
a case extending at least upto the 10th neighbourhood and the overlapping
of such zones of influence of cases, present and past, seems to
be the most probable explanation for the wide scatter of infection
in the community. Prevalence of infection among child contacts was
definitely higher in case clusters. But, the significance of this
could be understood only from a study of the incidence of disease
during subsequent years in different types of clusters. It is significant
that only 10% of the total infected persons in the community were
found in case clusters. The case yield in general population, cluster
contacts, household contacts and symptomatics attending general
health institutions have been also compared. The case yield in the
last group (10%) is much higher than the case yield from both types
of contacts (0.7% and 0.6%) which where only slightly higher than
the case yield from the general population (0.4%).
|KEYWORDS: RURAL, HOUSEHOLDS, CLUSTERS, CASE,
SUSPECT CASE, CONTACT, PREVALENCE, INFECTION, DISEASE, SURVEY.
|SOME ASPECTS OF CHANGES IN RURAL POPULATION AND
FATE OF TB CASES AFTER AN INTERVAL OF TWELVE YEARS
|MS Krishnamurthy, KR Rangaswamy, AN Shashidhara &
GC Banerjee: NTI Newsletter, 1974, 11, 1-7.
During second epidemiological survey carried out
in 1972-73, special efforts were made in 21 of 62 villages belonging
to first survey (1961-62) to study the demographic changes and fate
of TB cases after an interval of 12 years.
The findings were: The increase of dejure population
was about 20% over a period of 12 years i.e., an annual increase
of 1.7%. The age structure had altered mainly due to significant
increase in the age group 60 years and above 51% to 64% indicating
aging of population. The loss of original population after 12 years
was 44%, of which 33% was due to migration and 11% due to death.
The overall migration was more among females. The migration rate
was higher in younger age group, being highest in 10-19 years (49%),
next in 0-9 years (38%). Thus, overall migration in 0-19 years was
43%. The death rate was highest in 60 years and above (58%). It
varied from 4-9% in age group 0-39 years. Original population available
after 12 years for re-examination was 56%. Distribution in different
age groups were; 0-9yr = 57%, 10-19yrs = 47%, 20-49yrs = 66%, 50-59yrs
= 44%, 60yrs and more = 28%.
Out of 88 X-ray suspect cases of earlier survey,
87 could be identified and present status of 72 were known. Of them,
16 were normal, 12 and 4 found to be suspect cases and bacillary
cases respectively and 40 had died. Of the remaining fifteen, 11
migrated and 4 not examined. Out of 14 bacillary cases, 13 could
be identified. Of them, 3 were sputum negatives (2 normal and 1
suspect case) 9 had died and 1 migrated.
|KEYWORDS: FATE, CASE, SUSPECT CASE, MORTALITY,
MIGRATION, RURAL POPULATION, DEMOGRAPHIC CHANGES, SURVEY.
|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.
|RELAPSE AMONG NATURALLY CURED CASES OF PULMONARY
|AK Chakraborty & GD Gothi: Indian J TB 1976,
The five year longitudinal epidemiological study
in south India (1961-68) showed that a considerable proportion of
bacteriologically proven cases found in a survey got cured naturally
without the facility of organised treatment in the survey area.
This "natural cure" could be an epidemiologically significant
phenomenon- depending on the stability of such a cure or in other
words, the frequency of relapses among the naturally cured. In all,
108 naturally cured cases of tuberculosis out of a total of 269
cases, from among about 62,000 persons surveyed twice, were followed
up for varying periods of 1 to 3½ years.
It was observed that the average relapse rate was
85.4 per 1000 person years of observation, there being no difference
between the two sexes. Relapse rates were however higher in persons
aged 20 and more compared to those 5-10 years old. Relapses were
not dependent on the bacteriological status at initial diagnosis
i.e., whether positive by culture alone or positive by smear and
culture. The death rate among the naturally cured was 42.7 per 1000
person years and together with relapse constituted the unfavourable
fate after natural cure. It has been calculated that as an input,
adding to the pool of bacillary cases in the community, the ratio
of relapse cases to cases arising afresh from the general population
in a year would roughly be in the order of 1:16. It is concluded
that the naturally cured status could be considered as an epidemiologically
favourable situation, though much less so when compared to the chemotherapeutically
|KEY WORDS: RELAPSE, NATURAL CURE, CASE, RURAL
|IS TUBERCULOSIS DECLINING IN INDIA?
|KS Aneja & AK Chakraborty: NTI Newsletter 1978,
Because of slow nature of decline and the long
span of the declining phase spread over a couple of centuries it
is difficult to obtain direct evidences of decline by conducting
studies over relatively short period of time and comparing the rates
so obtained. Therefore, one has to take into account the total current
epidemiological situation by considering both indirect and direct
evidences to know the trend of disease; A) Indirect Evidence i)
tuberculosis morbidity being largely confined to older age groups,
prevalence rates being similar in both rural and urban areas and
a wide gap between infection and disease rates (38% and 0.4% respectively).
ii) Information on tuberculosis mortality although not very reliable,
still appears to suggest that the disease, since the turn of the
century, has taken a declining course. It has been observed to be
253 for 100,000 persons in 1949 in Madanapalle and 84 per 100,000
in Bangalore during 1961-68. There might he some regional variations
but there is definite suggestion of decline in the mortality. iii)
Considerable change in clinical presentation from more acute and
exuberative to a more chronic disease and a shift in age during
last quarter of the century, a marked decrease of the concomitant
problems of pulmonary tuberculosis, are all indirect indicators
of decline. B) Direct evidences are: i) Information available from
various epidemiological surveys in India indicates no change in
the prevalence rates of bacillary tuberculosis in the country during
the last two decades. ii) The longitudinal survey conducted in south
India and the other in Delhi have shown a declining trend of the
disease specially in the younger age group. However, to see that
the trend is secular or not, these surveys have to be continued
for a longer period of time - atleast 15-20 years.
From the above evidences it may be reasonable to
infer that there is a gradual but slow natural declining trend of
tuberculosis in the country. To hasten the process of natural decline
and to give relief to a large number of prevailing cases, anti tuberculosis
measures should be further strengthened.
|KEY WORDS: TREND, SURVEY, INDICATORS.
|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.
|MORTALITY AND CASE FATALITY OF TUBERCULOSIS CASES
DIAGNOSED IN A RURAL POPULATION OF SOUTH INDIA
|VV Krishna Murthy: NTI Newsletter 1982, 19, 8-13.
Mortality from tuberculosis is an important epidemiological
parameter for defining the problem of tuberculosis in any country.
But due to lack of systematic recording and reporting system, precise
information on cause of death is not available in our country. An
attempt has been made to estimate the case fatality of tuberculosis
cases as well as mortality of cases diagnosed in a longitudinal
study conducted from 1961-68 in Bangalore district. Crude mortality
of cases is defined as the ratio of total deaths observed among
cases to the total number of cases observed, while case fatality
is defined as the ratio of deaths that have occurred due to tuberculosis
to the total number of cases investigated.
The overall observed annual crude mortality was
14.8%, while among culture positive smear positive (C+S+) it was
21%. An upward trend was seen with the increase in the age. The
overall annual crude mortality among culture positive smear negative
(C+S-) cases was 9.5% which is significantly lower than that among
C+S+ cases. The death rates among old and new cases at the end of
18 months were 16.7% and 13.7% respectively. No statistical difference
was found in the crude mortality either among old and new cases
or in relation to the interval of diagnosis. Case fatality due to
tuberculosis was computed by calculating the deaths among non-tuberculosis
population of the same area and during same period and eliminated
from the total deaths observed among tuberculosis cases. The case
fatality of tuberculosis was found to be 13.3%. It was further observed
that out of the total 38 deaths among cases, 89% were due to tuberculosis
and 11% were due to non-tuberculosis causes.
|KEY WORDS: MORTALITY, CASE FATALITY, CASE, RURAL
|ARE THE ABSENTEES FOR EXAMINATIONS IN THE EPIDEMIOLOGICAL
SURVEY OF TUBERCULOSIS DIFFERENT FROM THOSE EXAMINED?
|VV Krishna Murthy & KT Ganapathy: NTI Newsletter
1989, 25, 15-21.
It is a common observation that in epidemiological
surveys all those eligible for various examinations (tuberculin,
X-ray and sputum examinations) do not attend them. If the 'non-attenders'
differ from the 'attenders' the true situation of the problem may
not be known. In this paper, the prevalence of infection, bacillary
cases and suspect cases at II survey for both attenders and non-attenders
of the I survey from longitudinal study conducted by National Tuberculosis
Institute, Bangalore, are compared.
It was observed that in spite of repeated attempts,
nearly 1/5th of the population did not attend examinations. The
non- response group during I survey was examined at the subsequent
survey and both response and non- response groups at the preceding
survey were compared. It was found that in respect of prevalence
of infection and bacillary disease, the two groups did not differ,
but the mortality and emigration was higher among the non- response
group. Higher mortality among non-attenders may be due to the fact
that the group contained more sick people. The higher emigration
among non-attenders due to small error even to the extent of 0.5%
at the stage of census taking by registering a non-resident as permanent
resident of the village would highly boost the rate of emigration
among non- attenders. The difference in the indices of crude mortality
and emigration rates becomes narrower and narrower as coverages
for examinations increase. The analysis indicates that every attempt
should be made to obtain as high a coverage as possible in order
to obtain valid estimates of epidemiological indices in a population
|KEY WORDS: SURVEY, ABSENTEES, CRUDE MORTALITY,
|PREVALENCE OF TUBERCULOSIS IN A RURAL AREA BY AN
ALTERNATIVE SURVEY METHOD WITHOUT PRIOR RADIOGRAPHIC SCREENING OF
|AK Chakraborty, HV Suryanarayana, VV Krishna Murthy,
MS Krishna Murthy & AN Shashidhara: Tubercle & Lung Dis
1995, 76, 20-24.
Mass miniature radiography (MMR) is the usual tool
for population screening in tuberculosis case prevalence surveys.
However, this facility is not available at most centres in India.
An attempt was made to study the feasibility of carrying out sputum
positive case prevalence survey in a population by introducing methodological
variation in the screening, in order to select those eligible for
sputum test without resorting to the customary use of MMR for the
purpose. The study was carried out in Bangalore rural district during
1984-1986. The area was the same as for six earlier prevalence surveys
conducted since 1961. The population aged up to 44 years was tuberculin
tested. Persons with test induration size of = 10 mm were eligible
for sputum examination, besides all those aged over 45 years were
eligible. It was observed that 78.4% of the registered population
(29400) in the age group 10 years and above were required to undergo
sputum examination by the present method of screening leading to
a very high work load of sputum examination necessitating deployment
of additional sputum cultures. Thus, the purpose of pre selection
for sputum examination was hardly fulfilled. Further, a high contamination
rate was observed. The changed screening procedure in this survey
made comparison with the earlier data difficult.
The overall prevalence rate of cases was 438/100,000
in persons aged 10 years and above, while smear positive prevalence
rate was 68/100,000. The observed prevalence rate was similar to
earlier surveys, while smear positive prevalence rate was much lower.
In conclusion, the screening methodology was found to be operationally
unfeasible, ineffective and counterproductive to complicate the
survey procedure in the quest for simplicity.
|KEY WORDS: SURVEY, SCREENING PROCEDURE, SYMPTOMS.