California’s Plan to Trace Travelers for Virus Faltered When Overwhelmed, Study Finds

In the early days of the coronavirus outbreak, the United States, like many countries, had a very short chance of limiting the spread of the disease within its borders. Identifying travelers from high-risk countries and tracking their contacts with others would have been a critical step, if implemented in advance.

In California, the largest state and entry point for thousands of travelers in Asia, a program has been established to do just that. But its tracking system was quickly overwhelmed by a flood of passengers, many with inaccurate contact information, and was insufficient in some cases, making the program ineffective, according to a study released on Monday by the Centers for Disease Control and Prevention, which looked exclusively at California.


"Despite the intense effort, the traveler screening system did not effectively prevent the introduction of Covid-19 in California," the report said.

In early February, more than 11,000 travelers from China – and later from Iran – who landed in California were identified for contact tracking. The hope was to accompany people traveling from high-risk countries, allowing public health authorities to identify possible cases of coronaviruses, quarantine them and contact people exposed to them to limit the spread of the contagion.

But when the program started on February 5, several weeks had passed since the disease was first identified in Wuhan, China. On March 17, the program was abandoned so that health officials could shift their focus to mitigate the spread of the disease in the state. By mid-March, the coronavirus had already established a position in California; preventing further introduction abroad was seen as less important than fighting it on the ground.


"This report is a good example of the challenge of trying to use travel screening to contain and prevent the transmission of a pandemic," said Dr. Timothy Brewer, professor of medicine and epidemiology at the University of California, Los Angeles.

The report was prepared by the California Department of Public Health for the CD, which also provided similar information to passengers from other states.


A California health department spokesman said the report speaks for itself. When asked if traveler monitoring is a useful tool in combating a pandemic, the spokesman referred to a passage in the report noting that it can be effective if started early enough, but that it is particularly difficult with a respiratory illness like the coronavirus, with which transmission can occur before symptoms appear.

The report also said that traveler monitoring is most effective when there is accurate information about passengers and when the number of passengers does not overload the system. None of these conditions existed in this case.

Strict measures in smaller countries like New Zealand and Taiwan are believed to help contain outbreaks there, Brewer said. New Zealand instructed everyone who entered the country after the outbreak to spend two weeks in quarantine, and Taiwan instituted similar measures.

But these are island countries with much smaller populations, and Dr. Brewer noted that Taiwan began to install its restrictions "within a day or two after realizing that Covid-19 existed".


When passengers arrived in California on flights from China during the study period, their information was recorded by customs and border patrol officers and then forwarded to CDC, who in turn sent the contact information to California health authorities. . These names were given to health departments in local jurisdictions across the state for tracking and tracking contacts.


Iranian travelers were included in the program, called Return Traveler Monitoring, as of March 5. The study found that three of the passengers, including two from Iran, were later reported to the California Department of Health as Covid-19 patients.

In theory, after their arrival, travelers would be contacted to see if they developed symptoms and to find out who they had seen in person. If any of the passengers had symptoms or tested positive for the coronavirus, they could be isolated to prevent further transmission, and anyone with whom they came in contact could also be isolated.

The C.D.C. The report said that in California, incomplete information made it difficult to fully implement the plan. Sometimes names, addresses or phone numbers were inaccurate and passengers could not be found for follow-up.

In addition, the number of people to follow was overwhelming. During the seven weeks of the program, an average of 1,431 people from Asia entered California each week, according to the study. By comparison, passenger identification during the 2014-15 Ebola outbreak was effective in California, in part, because only 21 people a week came from affected countries in Africa.

The study also cited the issue of asymptomatic patients, who can spread the disease before showing signs of illness.

Still, the C.D.C. report approved traveler monitoring programs, although they are "likely to be most effective during the initial containment phase" of the outbreak.

Once the current California outbreak is under control, according to the study, public health officials should still try to implement the screening program, if another wave of illness arises. But he recommended that this be done in a more efficient and comprehensive manner, especially in the collection of accurate information about passengers.

The C.D.C. urged airlines to provide flight passenger lists to federal authorities and that health departments use text messages to communicate with passengers after they leave the airport. He said that all of these can be useful for "keeping disease rates low."

"The critical words are" low disease incidence, "" said Brewer. “What they are saying is that it could work if you understand the subject before your system overloads itself. Taiwan did. "

He added: "To do this correctly, you will need to have significantly more resources than are normally available in public health departments."

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