VIENNA, Austria (AP) A measles outbreak in and around the Austrian city of Salzburg has spread to about 180 people, most of them schoolchildren, authorities said Thursday.

An investigation has been launched to determine if negligence may have led to the spread of the contagious disease, said Marcus Neher, a spokesman with the Salzburg public prosecutor's office.

Officials were questioning employees and parents of children enrolled at a private school where the epidemic is believed to have started, Neher said. The probe was still in its initial phase and there was no concrete evidence against anyone yet, he added.

Countering criticism, the school said it never advised parents against vaccinating their children.

However, Hubert Hrabcik, director general of public health in Austria's Health Ministry, said the vaccination rate for measles, mumps and rubella, which are administered together, may have been "almost nil" at the school.

Austria strongly suggests, but does not require, that children be immunized against measles, among other diseases, and about 90 percent of children up to 14 are vaccinated.

Last year, there were 18 reported cases of measles in Austria, compared to 27 in 2006 and 10 in 2005, Hrabcik said.

He appeared optimistic that the "infection chain would soon be broken" but predicted a possible doubling in the number of cases.

Salzburg Gov. Gabi Burgstaller and Health Minister Andrea Kdolsky urged people under 40 who have not had measles to be vaccinated.

Five people between the ages of 16 and 30 have been hospitalized but all are on their way to recovery and one was released Thursday, Salzburg's Federal Medical Center said.

Once a scourge of children in Europe, measles spreads very easily, jumping from person to person through droplets emitted in sneezing or coughing. It is one of the most contagious diseases known, according to the World Health Organization.

An estimated 242,000 people, the majority of them children, died from measles in 2006, the latest year for which figures are available, the WHO says.