= Solution
Assume the 1000 individuals are initially disease-free. The event being counted is onset during the ten-year period, not occupancy of the pre-clinical state at its end. Using the estimated <transition intensity> as a constant onset rate and <linearity of expectation>, \b[the expected number of onsets] is
$$
\boxed{1000(1-e^{-0.005\times10})\simeq48.77,\quad\text{about }49\text{ people}.}
$$
The first-order approximation $1000\times0.005\times10=50$ is close, but does not account for depletion of the disease-free group.
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