BISMARCK — At the epicenter of the nation's COVID-19 outbreak, the virus complicates nearly every aspect of life — including travel.

Public health experts have strongly advised Americans to refrain from holiday gatherings with members of multiple households, saying a bump in COVID-19 cases resulting from Thanksgiving dinners could overwhelm hospitals across the country. Still, more than 3 million air travelers passed through TSA security checkpoints from Friday, Nov. 20, to Sunday, Nov. 22 — the most of any three-day period during the pandemic.

But with COVID-19 infection rates rising, some states have put in place mandatory quarantine periods and testing requirements for travelers deemed "high-risk." North Dakotans, South Dakotans and Minnesotans fall in this category for most states that have implemented restrictions due to the high degree of community spread in the Upper Midwest.

The Northeast, which was battered by the virus in the spring, has mostly tried to seal off the rapidly growing outbreaks in the rest of the country.

Visitors to New York from most states must present proof of a negative test upon arrival, then quarantine for three days and then test negative again before leaving quarantine.

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Vermont and New Hampshire require visitors from outside New England to quarantine for at least a week before seeking a test and leaving quarantine if it's negative.

Pennsylvania, Massachusetts, Rhode Island, Connecticut and Maine all have instituted mandatory quarantine periods for visitors that can be avoided with proof of a recent negative test.

Travelers from any other state to Alaska or Hawaii must show officials evidence of a negative test to avoid a quarantine requirement.

For months, New Mexico has maintained some of the strictest travel requirements in the country. All visitors to the Land of Enchantment must quarantine for two weeks no matter how recently they may have tested negative for the virus.

Visitors to the District of Columbia must present proof of a negative test upon arrival and then get tested again three to five days later to avoid a quarantine period. The city of Chicago requires a two-week quarantine for visitors from North Dakota, South Dakota, Minnesota and eight other states with severe COVID-19 outbreaks.

North Dakota has no travel restrictions of its own, though health officials say sick or recently sick residents shouldn't travel.

South Dakota has no statewide travel restrictions, but several American Indian tribes have shut down highway routes for the general public on their reservations.

Minnesota has no hard restrictions, but out-of-state travel is "highly discouraged" by health officials, and residents are asked to quarantine for two weeks upon returning to the state from elsewhere.