|RISK OF PULMONARY TUBERCULOSIS ASSOCIATED WITH EXOGENOUS
REINFECTION AND ENDOGENOUS REACTIVATION IN A SOUTH INDIAN RURAL POPULATION
- A MATHEMATICAL ESTIMATE
|VV Krishna Murthy & K Chaudhuri: Indian J TB
1990, 37, 63-67.
It has been reported that a substantial proportion
of the new cases arise from the previously infected population.
Hence, it appears that exogenous reinfection and/or endogenous reactivation
play a major role in the development of post-primary disease. Though
the risk of disease associated with exogenous reinfection and endogenous
reactivation has not been computed in Indian conditions, the data
collected during a longitudinal study by National TB Institute,
Bangalore was analysed to estimate the above mentioned risk rates.
The risk of disease associated with exogenous reinfection
was 6.55% per year compared with 0.21% yearly due to endogenous
reactivation. To test the validity of the computed risk rates these
were applied to the interval between the 3rd and 4th surveys. It
was then estimated that 64 new cases should have been diagnosed
in that survey interval as against 57 cases actually diagnosed.
It was also estimated that 1.9% of the total population would be
having recent infection, 1.3% would be previously infected with
recent reinfection and 32.7% with previous infection but no recent
infection leaving 64.1% who are not infected at all (uninfected).
Among the new cases diagnosed, 28% would have progressive primary
disease, 41% cases arise due to exogenous reinfection and 31% due
to endogenous reactivation. In other words, the 1.9% population
with recent infection contributes 28% of the total new cases, the
1.3% reinfected population contributes 41% and the 32.7% previously
infected population contributes the remaining 31% of the total new
|KEY WORDS: RISK OF INFECTION, INCIDENCE OF INFECTION,
EXOGENOUS REINFECTION, ENDOGENOUS REACTIVATION, RURAL COMMUNITY, MATHEMATICAL