The state Mosquito Management Program said Thursday that the unidentified Stratford resident is in his or her 60s, became ill in July and reported being bitten by mosquitoes.
The individual was not hospitalized and is recovering.
The illness was characterized principally by joint and muscle pain and diarrhea.
Since June 27, officials have identified mosquitoes that tested positively for West Nile virus at trap sites in 16 towns.
Theodore Andreadis, director of the state's mosquito testing program, said 21 people were infected with West Nile virus last year, with 15 by the end of August.
He says he does not anticipate that 2013 will be a bad year for human infections.