Tap water service provided clean water to 35.5%
(1971), 38% (1973), and 51% (1977) of the population,
and one person was able to access 173 L (1971), 179 L
(1973), and 304 L (1977) of clean water daily. At these
time points, the incidence and incidence rate changed
abruptly; the incidence rate fell below 10 persons/
100,000 persons in 1971, below 1000 persons in 1973,
and below one person/100,000 persons in 1977. These
data suggest that to prevent typhoid fever in the
community, it is necessary to provide clean tap water to
35.5% of the population and at least 173 L of clean
water per person every day. An appropriate availability