An infant in San Francisco has contracted the measles virus and is infectious, according to the SF Department of Public Health, in the first known measles case in the city since 2019.

The measles case was confirmed on Monday, April 13, according to the Department of Public Health, in an infant who is younger than 12 months. The infant had recently traveled internationally and became infectious upon returning to San Francisco, and the family of the infant is all reportedly vaccinated.

The department says that the risk to the general public from this case is "low," at this time, and they are conducting contact tracing with those who have been in contact with other family members. Those who may have been in contact with the infant or a family member will receive a phone call from the city department or the California Department of Public Health.

The measles virus is airborne, can be spread through breathing or coughing, and can remain in the air for up to an hour. Symptoms include fever, cough, runny nose, and conjunctivitis, as well as a rash that appears within four days. The most common cause of death for children with measles is pneumonia, which is a possible complication.

Infants are typically vaccinated against measles between 12 and 15 months of age, with a second dose administered between ages 4 and 6. Infants 6 to 11 months old can get the vaccine if they are traveling internationally.

"It is incredibly important to get the MMR vaccine, as measles is one of the most infectious diseases in the world," says San Francisco Health Officer Dr. Susan Philip in a statement. "If you and your family are traveling internationally, make sure everyone is up to date with the MMR vaccine and is aware of the symptoms of measles."

Measles has been on the rise in California among unvaccinated individuals, with 39 cases reported in the state so far this year. As the Chronicle reported just yesterday, there is an ongoing measles outbreak in Sacramento and Placer counties, with 17 cases reported there, and four just in the last week.

The first case in that outbreak appeared in an unvaccinated toddler who had recently traveled to South Carolina, which is in the midst of a widespread outbreak of nearly 1,000 cases to date.

Of the 39 cases in California this year, 85% have occurred in individuals younger than 20.

The last major measles outbreak in the state came in 2019, and California recorded 73 cases that year.