BOSTON -- Two human cases of West Nile virus have been confirmed in Massachusetts, the Department of Public Health confirmed Thursday.

The first patient, an elderly female resident of Worcester County, developed symptoms on Aug. 19 and was hospitalized, the DPH said. She has since been released from the hospital.

The second patient, a female resident of Middlesex County between the ages of 45 and 64, remains hospitalized, but is improving, the DPH said. Lexington Health officials confirmed Thursday that the case was a Lexington resident.

Based on recent mosquito testing results, residents across the state face an increased risk of exposure to West Nile virus, the DPH said. Ninety mosquito pools have tested positive for West Nile virus in Massachusetts this year, and aerial spraying for mosquitoes was conducted in southeastern Massachusetts in August, the DPH said. Standing water from last week's rains followed by the hot, relatively dry weather created favorable conditions for mosquitoes that carry the virus, the DPH said.

Recent rains will also favor mosquitoes that are capable of carrying both West Nile virus and Eastern equine encephalitis virus.

"Efforts to reduce the risk of mosquito-borne illness continue across the state," said DPH epidemiologist Dr. Al DeMaria. "Even so, we all need to continue to take simple, common-sense steps to protect ourselves and our families from mosquito bites.”

While EEE is almost always a severe, life-threatening disease, West Nile virus can also cause the same severe disease in some who are infected.

There were no human cases of EEE during 2009; however, there were 13 cases with six deaths from 2004 through 2006. EEE is usually spread to humans through the bite of an infected mosquito with symptoms beginning five to seven days later. EEE is a serious disease in all ages and can even cause death, the DPH said.

To reduce the risk of infection, people are advised to removes standing pools of water on their property, use insect repellent and wear long sleeves and pants in the evening.