Are illegal immigrants bringing ‘tremendous’ disease across the border, as Trump says? Unlikely

Are undocumented immigrants bringing high levels of infectious disease into the United States? That’s one of the claims made by Republican presidential candidate Donald Trump, who has made opposition to illegal immigration one of the cornerstones of his campaign.

"Tremendous infectious disease is pouring across the border," Trump said in a statement released on July 6, 2015. "The United States has become a dumping ground for Mexico and, in fact, for many other parts of the world."

This is the latest iteration of an old claim.

Last year, we fact-checked a statement by Rep. Phil Gingrey, R-Ga., that there are "reports" of undocumented minors reaching the border "carrying deadly diseases such as … Ebola virus." Because the outbreak of Ebola was occurring in Africa -- rather than in Central America, where most of the unaccompanied children were coming from -- we rated the claim Pants on Fire.

But Trump’s claim is broader. We wondered: Is he right about the threat to Americans’ health? We asked Trump’s camp for evidence, but they did not get back to us. We also asked the Centers for Disease Control, which referred us to the Department of Health and Human Services. HHS did not respond to our inquiries.

So we sought guidance from medical experts. Their consensus was that there’s essentially no hard data on the question of whether unusual levels of disease are flowing into the United States due to undocumented immigrants.

For this reason, we aren’t putting Trump’s claim on the Truth-O-Meter, but we thought readers would be interested to hear what we found.

The CDC, on its website, acknowledges that there’s a risk, though it’s important to note that the risk doesn’t stem exclusively from undocumented immigrants. Indeed, they probably represent a distinct minority of border crossers. Approximately 300 million legal crossings take place from Mexico into the United States annually along the 1,969-mile border, and about 15 million Americans visit Mexico each year, according to CDC.

"The sheer number of people who live, work, and travel between the United States and Mexico has led to a sharing of culture and commerce, as well as the easy transportation of infectious diseases," CDC writes on its website. "The large movement of people across the United States and Mexico border has led to an increase in health issues, particularly infectious diseases such as tuberculosis."

For this reason, CDC and its Mexican counterpart have established a disease-surveillance infrastructure on the border.

CDC specifically cites the possibility of the cross-border movement of "HIV, measles, pertussis, rubella, rabies, hepatitis A, influenza, tuberculosis, shigellosis, syphilis, Mycobacterium bovis infection, brucellosis, and foodborne diseases, such as infections associated with raw cheese and produce," though vaccination has helped reduce the risk.

So what outbreaks have been reported at the border? Not many.

In July 2014, when a surge of undocumented minors from Central America was heading toward the U.S.-Mexico border, a union that represents border patrol officers announced that an agent had been diagnosed with scabies while processing such migrants. Scabies is an itchy skin condition caused by a mite that is highly contagious, though also easily treated, according to the Mayo Clinic. It’s analogous to head lice.

A more serious risk -- if it materialized, which it hasn’t -- is tuberculosis. Tuberculosis is more common in other countries it is in the United States. But border officials are well aware of the threat and are on the lookout.

A spokesman for the HHS Administration for Children and Families told NBC News in 2014 that "when children come into the Department of Health and Human Services program, they are given a well-child exam and given all needed childhood vaccinations to protect against communicable diseases. They are also screened for tuberculosis, and receive a mental health exam. If children are determined to have any communicable disease or have been exposed to a communicable disease, they are placed in a program or facility that has the capacity to quarantine."

Meanwhile, Mark Ward of Texas Children’s Hospital, who is president of the Texas Pediatric Society, told NBC that "as might be expected from children that had endured long journeys, they are tired," and some had common diarrheal and respiratory illnesses. Martin Garza, a Texas pediatrician who is caring for immigrants in McAllen, Texas, concurred, telling NBC that "they have common colds and other respiratory infections that kids get every day, stomach pain and constipation or diarrhea."

The experts we contacted agreed that there is no evidence of a massive influx of infections across the border.

"There is no evidence whatsoever that this is so," said Arthur Caplan, director of the division of medical ethics at New York University’s Langone Medical Center. "No study or survey shows this. There is no outbreak or bump in disease attributable to immigrants."

Thomas Fekete, the section chief for infectious diseases at the Temple University School of Medicine, agreed.

"When it comes to the health of immigrants, it is possible that undocumented folks have more health conditions that warrant concern, but I do not know of a scientific or quantitative assessment," Fekete said. "Workers are probably in decent health as the work itself is arduous. But there are some illnesses that occur more commonly in poor countries, such as tuberculosis, and some that occur more commonly because of farming or lifestyle issues, such as cysticercosis. But the notion that the Mexican government is orchestrating the movement of sick Mexicans to the U.S. is wacky."

He added, "Even if their health is in some ways worse than ours, we have the capacity to deal with this and produce minimum drag on our economy."