SALT LAKE CITY — Health department officials on Monday confirmed a fourth case of measles in Salt Lake County. Six more are suspected of having the highly contagious infectious disease and officials are stressing the voluntary quarantine that is in place.

As epidemiologists continue to make contact with individuals who might have been exposed to the initial case locally, they are finding more potential for infection, according to Salt Lake Valley Health Department spokeswoman Pam Davenport. She said the department is working to contain the measles outbreak and to minimize its effects on the community.

"It's very important to try to prevent the disease because the disease is very serious and it is difficult to treat," said SLVHD family health services director Audrey Stevenson. She said victims might have minor symptoms up to four days before a rash appears and remain contagious for up to four days afterward.

SLVHD first announced the local presence of the measles virus on Thursday. Since then, officials have fielded hundreds of phone calls and have asked unvaccinated individuals with potential exposure to remain on voluntary quarantine, meaning no school, church, shopping or recreational activities, Davenport said.

The affected individuals range in age from toddler to the late-teens, and some are siblings, said SLVHD executive director Gary Edwards. He said one victim was hospitalized for a short time upon infection.

Four schools have been impacted, including Olympus High School, where measles first turned up. At least 22 students are on leave from that school until April 25, when officials believe the disease will have run its course. Other schools where students have been asked to stay home include William Penn Elementary, where at least two are in jeopardy, and Evergreen Junior High and Skyline High schools, where a total of 42 students have potentially been exposed.

"For their own safety, we're removing them from the student populations," Granite School District spokesman Ben Horsley said Monday. Residents within the district boundaries should have been notified, via an automated phone system, of the current situation regarding the outbreak.

Horsley said less than 2 percent to 3 percent of the school's total populations are not immunized and those individuals are the ones being asked to stay home for the duration of the contagious period of the outbreak.

Two doses of the MMR vaccine are required for all schoolchildren in Utah, unless exemptions are obtained on the basis of religious or personal opposition, according to state law. Stevenson said that while there is a method to track child immunizations, there is no statewide system in place that tracks the same information for adults. Prior to the early '90s, students only received one dose of the vaccination, so much of the adult population could be at risk.

Measles, Davenport said, is a "vaccine-preventable disease" and requires the full two doses of vaccine to be effective. None of the infected individuals have been vaccinated to ward off measles specifically.

State and local health departments should have enough vaccine to treat those who want it and Edwards said the office is already petitioning the federal government for replenishment.

The last statewide outbreak, which originated in Washington County in 1996, ended up costing the state approximately $600,000. At least 107 individuals were affected at that time.

"Every outbreak is very different," Edwards said. "Back then there were few kids in school who had the second dose of the MMR vaccine … so it played out very differently."

The last Salt Lake County case of measles happened at the tail end of the outbreak, in 1997, while the most recent case reported in the state was in 2005. Anyone with questions and/or concerns about the most recent cases, is asked to call the SLVHD Health Hotline at 801-743-7280.

While officials believe the outbreak has been confined to the four aforementioned schools, the duration of concern for additional exposure won't be known until the middle of next week, Edwards said.