Two measles cases have been confirmed in Houston, marking the first reported cases in the city since 2018, according to the Houston Health Department.

The health department announced Friday that the two cases, in adults who live in the same household and have unknown vaccination statuses, are linked to international travel. Contract tracing is being conducted to identify possible exposures to others and to limit further spread of the highly infectious viral disease, which can cause serious complications in children younger than 5 years old, pregnant women and people with weakened immune systems.

"Measles is a serious but entirely preventable disease," Dr. David Persse, the city's health authority, said in a news release. "Vaccination is the best tool we have to protect individuals and the broader community from this highly contagious illness. Ensuring your immunizations are up to date is critical, especially in light of these recent cases."

Measles was declared eliminated from the United States in 2000, according to the Centers for Disease Control and Prevention, which says the disease remains common in other parts of the world and cases are brought into the U.S. annually by unvaccinated travelers.

Measles is spread through coughing, sneezing or by being close to someone who is infected with the virus, which can linger in the air for up to two hours after an infected person has left the area, according to the Houston Health Department. Symptoms include high fever, cough, rash, runny nose and red, watery eyes. Complications include diarrhea, ear infections, pneumonia or, in rare cases, brain inflammation.

People who are infected can spread the virus from four days before a rash appears through four days afterward, according to the city health department.

Those experiencing symptoms, or who think they have been exposed to measles, are encouraged to isolate themselves and contact a healthcare provider by phone.

As it investigates the confirmed cases, the Houston Health Department says it will post relevant exposure locations as well as dates and times to its website.

"Sharing this information helps individuals assess their potential risk and take appropriate actions to protect their health," the health department said in its news release.