3.8. Results of the longitudinal survey
As reported in the second chapter, about 60 NTI personnel
worked directly and almost everyone indirectly to complete the field work
which began in 1961 and ended in 1968 on schedule. It took nearly as much
time to analyse the data. Many experts came and assisted or interacted
as short term consultants. A summary report was published in the WHO Bulletin
in 1974. A fuller version is available in the library for reference83.
The paper, yielded vast credible information on the desired
objectives. It provided insights into the disease dynamics and became
a forerunner for new studies. The prevalence of tuberculous infection
in the population was found to be about 30%. The annual incidence of infection
was about 1%. The overall incidence of infection ranged from 1.61 to 0.85%;
the incidence of infection continuously increased in the higher age groups.
However, the prevalence and incidence of infection showed a significant
decrease during the five years in the age group 0-24 and 0-34. The average
annual incidence rate of disease ranged from 79 to 132 per 1,00,000 population.
The incidence among the newly infected (between two rounds) was seven
times the rate for those already infected. Those with >20 mm reaction
had higher annual incidence rate of disease. Out of the 126 cases followed
up during the 5 years, 49.2% died, 32.5% got cured and 18.3% continued
to remain sputum positive. The incidence cases showed a natural cure rate
of 20% and a mortality of 14% over the immediate observation period of
one and a half years. This showed a higher natural cure indicating that
TB cases were not a uniform entity. There could be gradations from the
point of view of diagnosis and ability to benefit from treatment83.
Disease Dynamics : Natural History of Tuberculosis