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Indian Journal of Community Medicine

Tuberculosis Trend Among Household Contacts Of TB Patients

Author(s): V.K. Dhingra, S. Rajpal, Nishi Aggarwal, D.K. Taneja*

Vol. 29, No. 1 (2004-01 - 2004-03)

New Delhi Tuberculosis Centre, New Delhi *Deptt. of Community Medicine, Maulana Azad Medical College, New Delhi

Abstract:

Research question: What is the prevalence of infection and diseases among household contacts of freshly diagnosed index tuberculosis cases.

Objective: To estimate the prevalence of infection and disease among household contacts of freshly diagnosed tuberculosis patients.

Study design: Cross-sectional.

Setting: New Delhi Tuberculosis Centre - An urban TB clinic in Delhi.

Participants: All household contacts of freshly diagnosed index cases of tuberculosis registered at New Delhi Tuberculosis centre.

Study variables: Age, sex, BCG status.

Results: A retrospective analysis of 1,052 household contacts of freshly diagnosed cases of tuberculosis was done to estimate the prevalence of infection and disease among them. Prevalence of infection among unvaccinated contacts (<20 years of age) was found to be 49.4% while the active tuberculosis disease among all the contacts was 4.3%. The disease rate was found to be higher among contacts aged 15-34 years. These findings have been compared with an earlier study among household contacts done within the same domiciliary area and have shown an increased prevalence of infection and disease among this high risk group as compared to the general population.

Keywords : Tuberculosis, Contacts, Delhi, Urban, Trend

Introduction:

Despite increased level of awareness and improved diagnostic facilities, tuberculosis still accounts for 3 million deaths in the world every year. In India alone, around 1.8 million new cases of tuberculosis are diagnosed annually; of whom about 0.8 million are sputum positive1. The basic principle of control of tuberculosis is treatment of infectious cases in early stages, thereby preventing the spread of infection. It is estimated that approximately 10% of those infected develop active disease during their lifetime.

Chemotherapy of infectious cases remains the main tool to cure disease and prevent further spread of infection, yet case finding is an important activity for control of tuberculosis. Case finding essentially means early detection of hidden sources of infection. WHO expert committee on tuberculosis in its ninth report noted that mass miniature radiography was a very expensive procedure for TB control even when the prevalence was very high. But selective case finding in high-risk groups is important in areas where adequate treatment facilities are available. Household members and close associates of tuberculosis patients comprise a high-risk group for tuberculosis and as such their examination carries great importance regarding prevention and control of tuberculosis.

Material and Methods:

Household contacts of freshly diagnosed 'index cases' of tuberculosis registered at New Delhi Tuberculosis centre between January to June 1995 and residing in the centre's domiciliary area were taken for the study. Index case has been defined as the first case in a household diagnosed at the centre to be suffering from tuberculosis.

A household for the purpose of this study has been defined as a family group generally living together and having a common cooking arrangement. Out of consecutive 300 index cases registered during the period, 278 were found suffering from pulmonary tuberculosis and 22 were having extrapulmonary tuberculosis. For the present study, household contacts were further divided into 3 groups:

  • Group I: Sputum smear positive pulmonary tuberculosis.
  • Group II: Sputum smear negative pulmonary tuberculosis.
  • Group III: Extra-pulmonary tuberculosis.

All the household contacts were called to the centre for examination. Most of them were examined within a week of the diagnosis of the index case. The examination varied with age of the contact. Contacts below 5 years of age were first Mantoux tested with 1 TU P.P.D. Those found negative to Mantoux test read after 72 hours i.e. showing less than 10 mm induration in transverse diameter, were BCG vaccinated and those found Mantoux positive i.e. showing induration of 10 mm or more, were X-rayed.

All contacts in the age group 5 years and above were X-rayed and a postero anterior chest X-ray was taken. Contacts between 5-20 years were also subjected to a Mantoux test in addition to radiological examination of chest. Two independent readers assessed the X-ray films. Further, investigations were carried out depending upon the above results. Shadows of doubtful tubercular or non-tubercular etiology were observed and if necessary, a course of broad spectrum antibiotic of short duration was given and the X-ray was then repeated. The diagnosis of active tubercular etiology was made only after a sufficient period of observation. All

The data was analyzed using MS Excel 2000 and Z test was applied.

Results:

Table I: Distribution of index cases and contacts according to different groups of tuberculosis.

  TB Total
Group 1 Group 2 Group3
No. of Index cases 72 (24.0) 206 (68.7) 22 (7.3) 300
No. of Contacts 289 (27.5) 684 (65.01) 79 (7.5) 1052
Average No.of contacts 4.01 3.32 3.59 3.50

Data of 1052 household contacts of 300 index cases was analysed to estimated the prevalence of infection and disease among them.

On an average 3.5 contacts were examined for each index case registered at the centre.

TB
Age
(in years)
Group 1 Group2 Group 3 Total
1,052
M F T M F T M F T
0-1 20 33 53 71 54 125 2 6 8 186
5 - 14 50 48 98 100 93 193 8 15 23 314
15 - 24 32 20 52 61 69 130 11 9 20 202
25 - 34 18 19 37 53 34 87 7 3 10 134
35 - 44 9 11 20 33 44 77 3 2 5 102
45 - 54 5 11 16 20 24 44 2 4 6 66
55 and above 6 7 13 14 14 28 5 2 7 48

Table III: Infection rate (tuberculin reactors) among vaccinated and unvaccinated contacts aged upto 20 years.

  Group 1 Group 2 Group3 Overall
  Total IR % Total IR % Total IR % IR %
BCG Vaccinated group
0 - 4 yrs 36 28 77.8 78 28 35.9 4 1 25 48.3
5 - 20 yrs 73 54 73.9 146 78 53.4 23 11 47.8 59.1
Total 109 82 75.2 224 106 47.3 27 12 44.4 55.6
Unvaccinated group
0 - 4 yrs 7 3 42.8 40 12 30 4 0 0 29.4
5 - 20 yrs 39 27 69.2 77 41 53.2 9 4 44.4 57.6
Total 46 30 65.2 117 53 45.2 13 4 30.8 49.4
Overall Infection Rate (IR) 155 112 75.25 341 159 46.6 40 16 40 53.54

All the contacts up to 20 years of age were examined for the presence/absence of BCG scar in order to assess infection rates among vaccinated and unvaccinated group. An overall 65.3% of the contacts between 0-20 years had BCG scar.

It can be observed from Table III that prevalence of infection among vaccinated and unvaccinated group was more or less same among the contacts of all the three groups. Overall infection rate among vaccinated group was 55.6% as compared to unvaccinated group in which it was 49.4%. Contacts between 5 and 20 years showed significantly higher infection rate as compared to 0-4 years age group both among vaccinated (z = 2, p<0.05) as well as unvaccinated group (z=4.71, p<0.05).

Contacts of group I showed significantly higher infection rates (72.3%) as compared to contacts of group II (46.6%) (z=4.04, p<0.05). Higher infection rates among contacts of sputum positive index cases are attributed to the presence of tubercle bacilli in the sputum of index case. Styblo2 stated that the bacillary status of the patient decides the extent to which he/she can transmit the tubercle bacilli to the other host, as prevalence of infection in child contacts of 0-14 years of age group of smear positive index case in a study carried out in Netherlands was observed to be 50% as compared to 6% in child contacts of smear negative index case and 1 % in the same age group among general population.

It is worth noting that the prevalence of tuberculosis infection in general population1 is about 44% as compared to overall infection rate of 53.5% in the present study among household contacts.

Table IV: Prevalence of tuberculosis among contacts.

Age (in years) Group 1 Group 2 Group 3 Total
0 - 4 0 2 0 2
5 - 14 2 8 0 10
15 - 24 8 5 0 13
25 - 34 3 5 1 9
35 - 44 1 4 0 5
45 - 54 1 2 0 3
55 + 0 2 1 3
Total Examined 289 684 79 1052
Active Disease 15 (15.2) 28 (4.1) 2 (2.5) 45 (4.3)
Inactive Disease 7 (2.4) 25 (3.8) 2 (2.5) 34 (3.2)

Table IV reveals that among the contacts of group I, the prevalence of active tuberculosis disease was 5.2% as compared to the contacts of group II (4.1%) and group III (2.5%) although statistically no significant difference was observed between group I and group II (z = 0.8; p>0.05).

This finding suggests that although priority should be given to sputum positive case, sputum negative cases are no less important. Comparatively higher prevalence of active disease in age groups 15-24 and 25-34 years was observed for all the groups.

Table V: Comparison between 1979 and 1995 studies.

Contact Group Study Period 1979 Study Period 1995
Extent of Coverage 94% 90%
Non-Responders 10% 10%
Total No. of Contacts examined 1986 1052
Average No of Contacts examined per Index case 3.6 3.5
Active Cases Found (%) 58 (2,9) 45 (4.3)
BCG Coverage 32.5 65.3
Infection Rate (%) (Unvaccinated group < 20 yrs) 59.8 49.4

Among the contacts studied during 1995, the prevalence of active disease was found to be 4.3% and was significantly higher as compared to 1979 study3 (2.9%), the different being statistically significant (z=2.02; p<0.05).

It suggests that over a period of 16 years, the disease has appreciably increased among the contacts.

Table VI: Comparison of infection and disease rates in contacts of different age groups during 1979 and 1995.

  Infection Rate
(among unvaccinated contacts < 20 yrs)
Disease Rate
(Among all contacts in all age groups
1979 1995 1979 1995
Total Examined Mx +ve % Total Examined Mx +ve % Total Examined Disease % Total Examined Disease %
Group 1
0 - 4 104 34 32.7 7 3 42.8 976 36 3.7 289 15 5.2
5 - 20 244 161 65.9 39 27 69.2
Total 348 195 56.0 46 30 65.2
Group 2
0 - 4 79 18 22.8 40 12 30.0 868 19 2.1 684 28 4.1
5 - 20 265 165 62.3 77 41 53.2
Total 344 183 53.2 117 53 45.2
Group 3
0 - 4 13 2 15.4 4 0 0 142 3 2.1 79 2 2.5
5 - 20 39 27 69.2 9 4 44.4
Total 52 29 55.8 13 4 30.8
Total (All Groups) 744 (100) 407 54.7 87 87 49.4 1986 (100) 58 2.9 1052 (100) 45 4.3
  z = 2.44, p<0.05 z = 2.02, p<0.05

Mx +ve: Mantoux test positive.

It can be seen from Table VI that there has been a statistically significant change in infection rates (z=2.44, p<0.05) of the household contacts of TB cases since 1979 in the domiciliary treatment service area of our center.

Discussion:

Household contacts form a high yield group for selective case finding by radiological and other methods of screening. It is always advisable following notification of a case of tuberculosis that appropriate contact procedures be initiated with the aim of identifying other cases of tuberculosis. If the first notified or index case is one of primary tuberculosis, contact tracing is done to locate the source case; and if the index case has smear positive post-primary or reactivation tuberculosis, the concern is that other contacts may have been infected by the index case, although a source case may still be sought. Contacts of a tuberculosis patient are 10 to 60 times more likely to have the disease than the general population according to some studies4,5 and approximately 10-14% of all notified cases have been detected by contact screening6-8. In contrast to the above studies, certain authors9-11 have been less successful with contact procedures. The procedures may vary from region to region depending on the prevalence of tuberculosis, particularly smear positive tuberculosis, and the ethnic make-up of the population11.

It is worth noting that the overall prevalence of tuberculosis (active and inactive combined) among contacts reported from New Delhi Tuberculosis Centre in 1979 was 6.1% (Dhingra)3 as compared to 7.6% observed in this study. Overall, 4.3% active tuberculosis cases were discovered among contacts studied during 1995 as compared to 2.9% during 1979 study. Maximum number of active cases were between 15-34 year age group. Infection rate of 49.4% among unvaccinated contacts (below 20 years) of all the index cases was observed in the present study as compared to 59.8% in the 1979 study. Increase in active disease despite lower infection rates observed in the present study though interesting is difficult to explain since the methodology followed in both the studies was same.

The present study has also shown that contacts form a high prevalence group for tuberculosis but the contacts of sputum negative cases have no lesser risk than the contacts of sputum positive cases. Although a part of it could be accounted for by inclusion of some sputum positive cases in the sputum negative category (group II), since only two direct smear examinations had been performed for the diagnosis of index cases; nevertheless the finding is of great interest with regard to risk of transmission of infection. From the present study an overall 65.3% BCG coverage was assessed among all the contacts as compared to 32.5% in 1979 study reflecting improvement in tuberculosis control strategy. The revised strategy of National Tuberculosis Control Programme lays more emphasis on cure of infectious cases. The case finding activities are given lesser priority. It is stated that effort at increasing case finding should be made only after achieving 85% cure rate in already detected cases12. The revised strategy is in line with the recommendations made by World Health Organization. This, however, does not mean that the contact examination (a case finding activity), which was being carried out as a routine practice in various tuberculosis centres should have been discontinued, because this activity was available in the centers which also provided ideal treatment facilities. Contact examination has a valuable impact on health education and impresses on the family and community as a whole, the infectious nature of the disease and the need for proper and regular treatment. This results ultimately in greater adherence to treatment and improved cure rates. Moreover, contacts form an easily approachable group and can be motivated easily.

Reference:

  1. Dye C, Scheele S, Pathania V, Raviglione MC. Global burden of tuberculosis. Estimated incidence, prevalence and mortality by country. JAMA 1999; 282: 677-86.
  2. Styblo K. Epidemiology of tuberculosis. Bull Int Union Tuberc Lung Dis 1978; 53: 141-8.
  3. Dhingra VK. Disease among household contacts of tuberculosis patients. Ind J Tub 1980; 27(2): 88.
  4. Schilling W. Epidemiology and surveillance of tuberculosis in the German Democratic Republic. Bull Int Union Tuberc Lung Dis 1989; 65(2-3): 40-2.
  5. Enarson DA, Fanning EA, Allen EA. Case finding in the elimination phase of tuberculosis: high-risk groups in epidemiology and clinical practice. Bull Int Union Tuberc Lung Dis 1990; 65(2-3): 73-4.
  6. Payne CR. Surveillance of tuberculosis contacts? Experience at Ealing Chest Clinic. Tubercle 1978; 59: 179-84.
  7. British Thoracic Association. A study of standardized contact procedure in tuberculosis. Tubercle 1978; 59: 245-59.
  8. Capewell S, Leitch AG. The value of contact procedures for tuberculosis in Edinburgh. Br J Dis Chest 1984; 78: 317-29.
  9. Spencer-Jones J. Tuberculosis case-finding in coastal South-East Kent 1977-1981. Lancet 1983; 1: 232-3.
  10. Esmonde TFG, Petheram IS. Audit of tuberculosis contact tracing procedures in S. Gwent. Resp Med 1991; 85:421-4.
  11. . Hussain SF, Watura R, Cashman B et al. Audit of a tuberculosis contact tracing clinic. Br Med J 1992; 304: 1213-5.
  12. Sarin R, Dey LBS. Indian National Tuberculosis
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