A top US health official on Monday once again quashed claims of a link between a recent measles outbreak and illegal immigration into the US.

Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention (CDC), said there was no evidence to support claims made by conservative hardliners that measles is being imported to the US by undocumented immigrants. Most commonly, she said, measles reaches the US through unvaccinated Americans who travel to Europe or Asia.

“I know that immigration is a complicated issue and people have strong feelings about [it],” Schuchat said, speaking in an online conversation hosted by the National Press Foundation. “The thing to say is that the region of the Americas was the first region to actually eliminate measles.”

Schuchat explained that prior to 2000 there was a high importation of measles cases from Latin America, but since then countries in the region have promoted a rigorous public health campaign. Now, Mexico, Guatemala, Honduras and El Salvador have higher rates of measles coverage than the US, according to estimates by the World Health Organization (WHO).

“In fact, the year’s outbreak, associated with the Disney park, the US exported measles virus to Mexico. So we see the virus unfortunately going the other direction,” Schuchat said.

There have been 154 confirmed cases of measles in the US this year, a majority of them linked to initial exposure at California’s Disneyland theme park. According to the CDC, 17 states and Washington DC have reported cases of the disease. Canada and Mexico have also reported cases stemming from the Disneyland outbreak.

Anti-immigration reform advocates have tried to force a connection between a disease and immigration. Last year, during the height of panic in the US over Ebola, health officials were forced to debunk claims that undocumented children fleeing poverty and violence in Central America were carrying the disease, which was affecting countries in west Africa.

Schuchat responded to such claims before a Senate health committee earlier this month, telling lawmakers the current measles outbreak could most likely be traced back to a strain that came from the Philippines, which saw its immunization structure destroyed by a typhoon in 2013.

In a follow-up question during the meeting, Senator Bill Cassidy, a Republican from Louisiana, asked if it were possible some immigrants might have “fallen between the cracks”. Schuchat pointed out that the current outbreak is spreading not along the US-Mexico border but in “some of the wealthier communities in California”.

Prior to the hearing, Representative Mo Brooks, a Republican from Alabama, said in an interview: “I don’t think there is any healthcare professional who has examined the facts who could honestly say that Americans have not died because the disease is brought into America by illegal aliens who are not properly healthcare screened, as lawful immigrants are.

“Unfortunately, our kids just aren’t prepared for a lot of the diseases that come in and are borne by illegal aliens.”