Used in medical, epidemiological, and public health contexts to describe the proportion of a population that becomes infected.
The infection rate in this area has dropped since last month.
As vaccination progressed, the infection rate decreased.
陽性率 refers specifically to the 'positivity rate' of tests, while 感染率 refers to the actual infection rate in a population.
Compound of 感染 (kansen, 'infection') and 率 (ritsu, 'rate').