As a cluster of measles cases grew in an elementary school in southern Florida, the state’s surgeon general sent a letter to parents that contradicted widespread medical guidance about how to keep the disease from spreading.

Doctors and health officials typically recommend that children who are not vaccinated for measles isolate for 21 days after they have been exposed at school. In the letter, the state surgeon general, Dr. Joseph Ladapo, said it was up to parents and guardians to determine when their children can attend school, even if those children have not been vaccinated against the disease.

“Because of the high likelihood of infection, it is normally recommended that children stay home until the end of the infectious period,” the letter read. However, the state Department of Health “is deferring to parents or guardians to make decisions about school attendance,” the letter, sent to parents at Manatee Bay Elementary School in Weston, Fla., continued.

Dr. Ladapo added that these recommendations might change in the future and stressed that children with measles symptoms should not go to school. As of Friday, there were six confirmed cases at the school, according to Broward County Public Schools.

Measles is one of the world’s most infectious diseases. Cases and deaths have been rising across the globe, in part because health officials have struggled to vaccinate people in the wake of the coronavirus pandemic and growing vaccine hesitancy. In January, the Centers for Disease Control and Prevention warned physicians to “stay alert for measles” as more cases emerged in the United States, largely among unvaccinated children and adolescents.

Dr. Ladapo, a former clinical researcher at the University of California, Los Angeles, has played a prominent role in the administration of Gov. Ron DeSantis, a Republican, appearing with the governor at events that mainstream public health experts have repeatedly criticized as spreading dangerous falsehoods.