LOS ANGELES — Public health officials in Los Angeles have declared a measles outbreak in the county, making it the latest metropolitan area to be hit by the illness and part of a national surge in cases rapidly approaching record numbers.

Five cases of measles are being investigated by the Los Angeles County Department of Public Health. Though vaccination rates are typically high in California, a single case can easily spread — not only to those who are not vaccinated, but also to infants who cannot yet receive immunization and to elderly patients with suppressed immune systems.

The public health department said the transmissions are the first confirmed in the county this year. The department believes additional exposures may have occurred in April at Los Angeles International Airport, at several buildings on the University of California Los Angeles campus, at a library at the California State University in Los Angeles, and at several restaurants near Glendale.

[Get answers to common questions about the measles outbreak.]

Officials did not indicate the ages of those infected but said the majority of individuals were unvaccinated.