Measles Cases are Rising. Here’s What to Know About Symptoms.

Health officials are raising alarm about the spread of measles in the United States and across the globe.

On Monday, the Centers for Disease Control and Prevention released a health advisory urging people over the age of 6 months who are traveling internationally to get vaccinated against the highly infectious virus. The agency also said that anyone returning to the United States from abroad should watch out for measles symptoms for three weeks after they arrive home.

Here’s what to know about how the virus spreads and what its symptoms look like.

How and when measles spreads

Part of what makes measles so tricky to contain is that infected people can easily spread the virus before even realizing they have it. Someone with measles can transmit the infection for up to four days before developing a telltale rash, according to the C.D.C.

Measles spreads when someone who is sick coughs or sneezes, said Dr. Paul Offit, a vaccine expert at the Children’s Hospital of Philadelphia. The virus can linger in the air for up to two hours after an infected person leaves a room. People can also contract measles by touching a surface that a sick person has contaminated and then touching their eyes, nose or mouth. “It’s the most contagious of the vaccine-preventable diseases,” Dr. Offit said.

Symptoms to watch out for

It typically takes one to two weeks for someone to feel ill after coming into contact with the virus. The earliest symptoms tend to be a cough, runny nose, pink eye and a fever. Some people may have a fever that goes above 104 degrees, which can be particularly dangerous for young children. Fewer than one in every 10 people with measles will also develop diarrhea, according to the agency.

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