|INCIDENCE OF TUBERCULOSIS CASES IN CONTACTS - A
|AK Chakraborty, Hardan Singh & P Jagota: Indian
J Prev & Soc Med 1980, 11, 108-11.
Contact examination is not recommended as a routine
procedure for Case-finding in the District Tuberculosis Programme.
The rationale for not including contact examination as a routine
Case-finding measure is: (1) prevalence rate of tuberculosis among
the contacts is not much higher than in the general population (2)
at the time of diagnosis of an index case, a second case may not
be found in the same household. Though more prevalence cases cannot
be diagnosed by contact examination, is it possible that by keeping
the household contacts, as a group, under surveillance, future incidence
of cases in the community can be substantially prevented? A model
situation has been created by using hypothesis derived from various
studies conducted in India, designed to answer the question. Variables
used in the model are: 40% of the general population are infected
at any point of time, there is only one prevalence case of TB at
any given point of time in an average household of five, 40% of
the non-infected population in a contact household are infected per
year, incidence of disease among newly infected group is seven,
times of the incidence among previously infected, incidence of disease
in general population is 0.13% and from among previously infected
persons 0.3% per year develop sputum disease.
At an incidence rate of 0.13% per year among general
population aged >5 years, it is expected that 111 cases would
arise in a year in the population of 1,00,000 under study. Thus,
of the 111 cases occurring in the community, 101 arise from those
who are not contacts.
The proportional contribution of new cases from
the contact group to the total incidence cases in the entire community
is so small, that even if all the contacts are kept under surveillance,
BCG vaccinated or placed on chemoprophylaxis, still over 90% of
incidence cases cannot be prevented from occurring. This is apart
from the fact that keeping them under surveillance will be highly
costly and is an operational problem of considerable magnitude.
|KEY WORDS: INCIDENCE, CASE, CONTACTS, MODEL