Travelers landing at Honolulu International Airport have their temperatures checked upon arrival, must provide contact information and are required to wear masks. There are no such rules for those on domestic flights at Atlanta’s Hartsfield-Jackson International Airport.

Several U.S. carriers now require travelers to fill out health questionnaires when they check-in, but only one — Frontier Airlines — mandates a temperature scan before boarding.

Several months after the novel coronavirus pandemic devastated the nation’s aviation industry, there still is no uniform strategy for managing the virus as travelers begin to return to the skies. The Trump administration has largely left it to airlines and airports to decide how to implement and enforce recommendations from the U.S. Centers for Disease Control and Prevention, saying they know best.

The result is a patchwork of responses, which some worry will hamper efforts to control the spread of the virus and undermine recommendations from public health officials about the importance of wearing masks and practicing social distancing.

When it comes to public health messaging, “consistency is critically important,” said Lisa Lee, an epidemiologist and public health expert at Virginia Tech.

“Imagine how it would have been for [the Transportation Security Administration] if after 9/11, if some airports allowed a whole gallon of shampoo and others only let you bring three ounces,” said Lee, who is also an associate vice president for research and innovation at the university. “It’s hard enough to get people to change behavior, and it’s really hard when the rules are confusing and unclear.”

Though passenger volumes are nowhere near where they were pre-pandemic, recent statistics from the TSA show the number of people screened at U.S. airports daily is slowly increasing after it dropped below 90,000 in mid-April, which some argue underscores the need for a unified response. The uptick comes as the number of confirmed cases is spiking in many states forcing some, including Texas and California, to rollback their reopening plans and restore some restrictions.

The coronavirus poses a risk to people in many settings, but air travel has been of particular concern in part because of the speed in which it can move infected people from one place to another, potentially seeding new clusters of infections.

“Airports and airlines are mass gathering and mass dissemination events,” said Ali S. Khan, dean of the College of Public Health at the University of Nebraska Medical Center and former director of the CDC’s Office of Public Health Preparedness and Response. “You bring all these people together, which markedly increases the risk [of transmission].”

This month, 26 passengers on a flight from Pakistan to Hong Kong tested positive for the virus. They were identified because Hong Kong requires that incoming passengers be tested. After 24 days with no new cases, New Zealand reported two new infections — both of them women who traveled to the country from the United Kingdom.

Airports may play a role in the spread of infectious diseases, but if managed correctly, health experts say, history has shown they can also serve as useful settings for controlling and tracking outbreaks before they gain a foothold in the larger community

International groups including the International Civil Aviation Organization and the International Air Transport Association have called for a coordinated approach. Earlier this month, in consultation with the United States and other governments, the ICAO published guidelines it recommended all airports and airlines follow, including using technology to reduce the amount of time people spend at the airport, temperature scans and detailed health questionnaires to identify sick travelers.

“The restart will go much more smoothly if governments cooperate,” said Alexandre de Juniac, IATA’s director general. “As I have said before, we must avoid the mess that followed 9/11 when governments acted unilaterally. This created confusion for airlines and travelers alike. And it took many years to clean up.”

The lack of federal standards has also frustrated many front-line workers, including pilots and flight attendants, who were among the first to call for mandatory mask policies and federal standards for cleaning aircraft. They have been joined by more than a dozen Democratic lawmakers who have appealed to Vice President Pence, Transportation Secretary Elaine Chao and FAA Administrator Stephen Dickson to take more aggressive action.

In particular, they want the department to take the lead in crafting a plan for dealing with the virus in the aviation sector. The Government Accountability Office called for that in a 2015 report published in the wake of the Ebola and SARS outbreaks, but the report was never completed in part because transportation officials said the CDC should take the lead.

Sens. Richard Blumenthal (D-Conn.) and Edward J. Markey (D-Mass.) are behind a renewed push to create a plan and have introduced legislation to create a task force to bring the agencies together.

Even so, federal transportation officials said they think the current process works.

“The airlines understand the position that they are in,” Chao said in a recent interview with The Washington Post. “They want to protect the flying public. These are their future customers. They also know they have to work well with their own workforce.”

When questioned at a recent Senate hearing, Dickson said his agency views its role as that of a “facilitator,” not a regulator.

“With respect to public health, that’s the CDC, and of course, they have responsibilities for sectors of transportation,” Dickson said.

FAA might offer guidance, but “these will not be regulatory mandates,” he added.

The back-and-forth has frustrated those who think the government needs to take a bigger role, putting teeth behind recommendations for face coverings and social distancing and setting specific rules for cleaning and contact tracing.

“It’s not right, and it’s not responsible,” said Rep. Peter A. DeFazio, (D-Ore.), chairman of the House Transportation and Infrastructure Committee. “This administration wants to stick its head in the sand and say, ‘It’s not our responsibility.’ ”

During a recent committee hearing on the impact of the pandemic on the transportation industry, DeFazio acknowledged that airlines have taken some steps, such as requiring travelers to wear masks, but said without federal backing to reinforce the mandates, travelers might not follow the rules.

Compliance can indeed be spotty. On a recent day at Baltimore-Washington International Marshall Airport, the vast majority of people wore masks as they entered the main terminal and moved through security checkpoints, but by the time they reached the gate areas most had taken them off.

To health experts like Virginia Tech’s Lee, that’s a prime example of how easily efforts to prevent the spread of the virus can be undone.

“I’m not surprised at the moment there’s a huge patchwork of responses,” added Henry Wu, an assistant professor at the Emory University School of Medicine, and director of the Emory TravelWell Center.

Wu said while there are certainly regional variances in virus spreads, it’s possible to create standards that offer airlines and airports flexibility but also give consumers a clear sense of what’s being done to protect their well-being.

Others disagree.

“I think the CDC and government have done a good job on putting out the right level of guidance,” said Jake Filene, senior vice president for customers at Frontier Airlines, which made preflight temperature checks a requirement for flying. “I think it’s fair to let the individual carriers decide on their own. It’s not a one-size fits all.”

But others say they would welcome more guidance from the federal government.

Hawaii, which has enacted some of the strictest measures in the country, said it felt it couldn’t wait on the federal government to act. In addition to the measures the state has in place, officials said they’ll spend $36 million on a thermal scanning system that will enable them to monitor passengers for signs of fever.

“It would be helpful for the federal government to do this uniformly so there is consistency,” said Tim Sakahara, spokesman for the Hawaii Department of Transportation. “Logistically, it would be better to do it everywhere.”

Sara Nelson, president of the Association of Flight Attendants-CWA — which, along with the Air Line Pilots Association, has been among the most vocal groups calling for national standards for aviation — argues that rules backed by federal enforcement help the industry and travelers.

“If you have rules in place you can stop the virus at the door,” she said. “We have decades of experience in this. The airport is one place where you can track and control the spread of disease.”

Ian Duncan and Katherine Shaver contributed to this report.