There has been no cases of intra-infection for nearly two months.
There has been not been any cases of infection within the cities for nearly two months.
「市中」を訳すと"in the city" または、"within the city"だと思いますが、"intra"とは"inside"（中）という接頭辞なので、"intra-city"という単語を使っても通じると思います。
「二か月近く」は"for nearly two months"と訳しました。
Sentence in context:
"It's hard to decide when to open our borders to tourists from abroad, but at least there has been no cases of intra-city infection for about two months."
アメリカ合衆国 
