Because we're actually talking about a set of numbers here, we do want to say "numbers," not "number," yes. E also changed the meaning of the sentence, though. There are "reported cases" of Lyme disease - the cases that actually get reported to the authorities - and that number is presumably smaller than the actual number of cases, because some people don't go to the doctor or get misdiagnosed or whatever.
The original sentence talks about the "reported cases" and tells us that NJ is high on the list of states in terms of reported cases. Option E mentions only the "cases" - meaning the actual number of cases. Perhaps NJ just has a really good reporting mechanism, and other states have a lot more cases but they don't get reported properly or something... we don't know that NJ actually is in the top 5 in terms of actual total cases - only reported cases.
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