Even with all of the health and safety protocols and enhanced sanitation measures that have been implemented at American airports and aboard aircraft, air travel remains a potential source of viral spread. We've seen this with plenty of countries around the world, and even some U.S. states, whose borders are open only to those with recent, negative COVID-19 test results in-hand, and no one wants to import new cases into communities that are already struggling to get a handle on community spread. And, with the wave of infection that continues to rise in America today, most domestic destinations also fall into that category.

To inspire consumer confidence and smooth the travel process for those whose destinations require proof of a negative test for entry, select major U.S. airlines have begun partnering with health companies to offer preflight COVID-19 tests to customers. Tests can cost anywhere from $70 to $150 each. Testing processes will vary by airline, but CBS News reported that all encourage passengers to take their tests within 72 hours of boarding. The following is a rundown of the various coronavirus testing services currently being offered by U.S. carriers.

While it doesn't offer testing onsite at airports, Alaska Airlines has partnered with multiple providers who offer COVID-19 testing to streamline travelers' paths to destinations that require a negative test result. Testing through these companies is available by appointment, in-person or at drive-thru collection sites, or through at-home kits. More information is available here.

American Airlines now offers preflight COVID-19 testing to passengers bound for either international or domestic destinations that have COVID-related travel restrictions. Customers can order the $129 test to take at home, then send their self-collected nasal swab to a LetsGetChecked lab for processing and receive their results within 48 hours. More information is available here.

While it doesn't offer testing nationwide, Delta Air Lines has announced a pilot program called "COVID-Tested Flight Trial" as a means to try quarantine-free travel from the U.S. to global destinations that require a negative test for entry.

Starting December 15, Delta is rolled out the Netherlands COVID-Tested Flight Trial from Atlanta's Hartsfield-Jackson Airport to Amsterdam, Netherlands. Passengers must take a PCR test five days prior to travel, as well as a rapid antigen test just before boarding their flight, and come up negative on both. A second PCR test will need to be taken upon arrival at Amsterdam Airport Schiphol for visitors to bypass quarantine. More information is available here.

Next, the airline will launch an Italy COVID-Tested Flight Trial, which begins December 19, flying out of Atlanta's Hartsfield-Jackson, New York's JFK or New Jersey's Newark Liberty Airport to Rome using the same criteria. More information is available here.

Frontier Airlines does not presently offer passengers COVID-19 testing but was the first to institute mandatory temperature checks for passengers and crew back in June. It has also heightened its disinfection protocols to meet best practices outlined by public health experts, requires all passengers and crew to wear masks at all times and utilizes hospital-grade HEPA filters aboard each aircraft.

Hawaiian Airlines has partnered with Worksite Labs to provide Hawaii-bound customers flying from either Los Angeles or San Francisco with exclusive access to drive-thru PCR testing sites. Passengers can expect to pay $90 for results within 36 hours or $150 for same-day results.

The airline also recently opened additional drive-thru and walk-up testing sites in Los Angeles, Las Vegas, Portland and Seattle.

Lastly, Hawaiian offers at-home, mail-in saliva test kits through Vault Health for $150 each. Test kits are express-mailed overnight to customers, who self-collect their sample with assistance from a testing supervisor in a video call. The samples are then overnighted to a lab and results are returned electronically within 24 hours. More information is available here.

JetBlue has also partnered with Vault Health to provide customers with access to FDA-approved, at-home, saliva-based COVID-19 testing. Tests are self-administered, with customers collecting their own samples under the oversight of a test supervisor via an online video connection. Their specimen is then overnighted to a laboratory for processing, and results are provided electronically within 72 hours.

As part of the arrangement, Vault Health provides JetBlue customers both with discounts on their test kits and a dedicated customer support phone line. JetBlue's website also notes that the cost of the test may be reimbursable by customers' insurance under the CARES Act. More information is available here.

CBS News reported that Spirit Airlines will begin offering PCR and rapid antigen COVID-19 tests at a dozen major U.S. airports, including Boston, Fort Lauderdale, Los Angeles, Minneapolis, Philadelphia and Seattle. Although it didn't specify which lab Spirit would be working in partnership with, pricing is said to be $69 for the antigen test, with results available in 30 minutes, and $99 for the PCR test, with results reported within 48 hours.

Southwest Airlines hasn't announced any partnerships to provide preflight COVID-19 testing at this time. The airline's set of enhanced sanitation and health and safety procedures, called the 'Southwest Promise', has seen the carrier working hard to protect passengers and employees since May. It includes round-the-clock cleaning and disinfection aboard aircraft and in airports; cabin ventilation run through HEPA filters; mandated mask-wearing and social distancing protocols; individual hygiene products on hand for passengers; and the continued suspension of in-flight beverage and snack service.

United Airlines is currently only offering COVID-19 testing as part of a few pilot programs from select airports.

Passengers traveling from San Francisco International Airport to Hawaii can take advantage of drive-thru testing onsite at the airport to bypass the Aloha State's quarantine rules (except on Kauai). Rapid antigen tests cost $250, and results are provided within about 15 minutes, while PCR tests run $105 and deliver results in around 48 hours. Testing is available by appointment only.

Passengers flying from Houston Intercontinental to select destinations in the Caribbean and Central/South America can arrange for an at-home, mail-in COVID-19 PCR test through United's partnership with ADL Health for $119 per test kit. The self-administered nasal swab must be collected and mailed back 72 hours prior to scheduled travel, and results are reported electronically within 24 to 48 hours. Eligible customers are sent information and instructions for purchase via email 14 days prior to their flight.

On select dates through December 18, passengers on United flight UA14 from New York/Newark to London Heathrow will receive free, onsite COVID-19 rapid antigen tests as part of a trial program. Advance appointments are required; results are delivered in approximately 30 minutes, and this testing is mandatory for passengers over the age of two to be allowed boarding.

More information on these programs is available here.