Coronavirus patients are presenting to emergency rooms after calling 911 from the United States-Mexico border.
"They will literally come to the border and call an ambulance," says Van Gorder, president and CEO of Scripps Health, a hospital system in Southern California.
The increased ambulance traffic from the border, which various officials described to CNN, is a symptom of the spread of the pandemic in the region, and a sign of the many connections between communities in both countries.
"There just isn't a wall for viruses at the border," says Josiah Heyman, director of the Center for Inter-American and Border Studies at the University of Texas at El Paso. "The wall is an illusion, because the two sides are really intertwined."
An increase in cross-border coronavirus cases, which began to draw public attention in May, overwhelmed some California hospitals and prompted the state to create a new patient transfer system to help.
"It is an unprecedented increase across the border," says Carmela Coyle, president and CEO of the California Hospital Association.
In the past five weeks, more than 500 patients have been transferred to hospitals across the state from California's Imperial County, which has the highest per capita rate of coronavirus cases in the state and, according to authorities, has seen a large number of patients crossing from Mexico.
But Van Gorder, Coyle, and other California officials say this is not an immigration problem.
Most coronavirus patients who cross the border, they say, are Americans.
In a call with state hospital leaders earlier this month, the head of the California emergency medical services authority, Dr. David Duncan, described the constant flow of patients arriving in Imperial County as "gas on fire".
"We have this continuous flow of Covid crossing the border in the form of US citizens who carry and continue to escalate and fuel the Covid pressures we see," Duncan said.
The view from the border
Authorities estimate that about a quarter of a million US citizens live across the border in the Mexican state of Baja California. Many work in the United States and have relatives there. Some regularly go to US hospitals when they need medical care. Others decided to cross this time because Mexican hospitals were overwhelmed by a large number of coronavirus cases.
"What happened as the situation worsened on the Mexican side of the line is that several American citizens are returning to the United States to seek care for Covid-19," says Coyle of the California Hospital Association.
Sergio A. Beltrán, US Customs and Border Protection Officer in charge of Calexico's ports of entry, said in a statement to CNN that he began to see an increasing flow of people crossing the border to receive medical care ago a few months.
"While it varies from day to day, and shift to shift, we have experienced a significant increase in calls related to medical care at Calexico ports of entry that can be directly linked to the COVID-19 pandemic in the last months". he said. "We are definitely seeing people on a daily basis. And we still have our regular medicine-related calls that are unrelated to COVID from people in accidents or who have other medical problems and are coming for medical treatment in the United States."
Sometimes people walk to the port of entry or head to the border crossing, then call an ambulance to take them to a US medical center when they arrive. And sometimes, he said, travelers arrive at the border in Mexican ambulances and have already agreed to have American ambulances find them there.
At El Centro Regional Medical Center in Imperial County, coronavirus cases began to increase in early May as the situation across the border in Mexicali worsened, says Adolphe Edward, CEO of the hospital.
"That rebound just took a quick and increasing movement," says Edward.
At one point in that month, the 161-bed hospital saw so many cases of coronavirus that it had to stop accepting new patients in the emergency room.
Edward says he heard first-hand from his own staff one reason why the numbers were going up.
"I have more than 60 staff members who travel back and forth every day. They live in Mexicali, but they come to work here," he says. "They told me that it took Mexicali a while to get to the point where they put restrictions (on social distancing). I think that's one of the reasons why the number is as high as it is now."
About 90 miles west, Scripps Mercy Chula Vista Hospital, which is across the border from Tijuana, was also seeing cases starting to climb.
Officials began tracking patients' travel stories there, and quickly spotted a trend – many had recently been to Mexico.
"About half of the patients who test positive indicate they have crossed the border the previous week," says Van Gorder.
"The patients who cross the border appear to be sicker than the patients we've normally been seeing," he says. "It may be that they have waited too long in Mexico or that they have gone to a Mexican hospital and decided to receive their care here."
& # 39; It's almost like a cascading waterfall & # 39;
The flow of patients across the border has been constant for weeks, says Coyle of the California Hospital Association. And now hospitals across the state, including northern Sacramento, are receiving Imperial County coronavirus patients as part of a new patient transfer system created to relieve pressure, Coyle said.
A challenge across the region, he says, is that many patients are sick with the same condition, requiring the same equipment for treatment at the same time.
"That is what drives the shortage of service and supply in Mexicali, driving these expatriates back to the United States and then driving a very unique movement of patients to the state of California and more broadly," he says. "It's almost like a cascading waterfall."
Van Gorder says he is concerned that officials are moving too fast toward the reopening.
"We still don't have our arms completely around Covid and the Covid spread," he says. "And as a border community, I think we have a double risk."
What is happening in other parts of the border?
Heyman of the University of Texas at El Paso says there is something important to remember about the coronavirus, and other problems, along the vast border between the United States and Mexico.
"The two parts cannot be kept apart," he says. "If there is a problem on one side of the border, it flows to the other side."
In the early days of the pandemic, Mexican officials expressed concern about travelers from the United States bringing coronaviruses into the country.
"I don't know what they thought they were doing," says Arturo Garino, mayor of the sister city on the US side of the border, Nogales, Arizona. But Garino says he is also concerned about the flow of people crossing the border.
While coronavirus cases are on the rise, particularly in two Arizona counties along the border, Santa Cruz and Yuma, Garino says authorities have not identified the cause.
"It has a lot to do with social distancing. It has a lot to do with meetings," he says. "And I know that many residents here go to Mexico and vice versa."
Garino, who recently signed an order requiring people in his city to wear masks in public places, says he is concerned about frequent cross-border travel that is part of daily life there and that intensifies the spread of the virus.
"I am concerned about the increase in cases that we have," he says. "We are trying to do everything possible to stop this virus, and we keep going up, up and up."
CNN's Cheri Mossburg contributed to this report.