LEWISTON — Students returning to Bates College this week will be quarantined for at least four days after they arrive.

The college told students this week that instead of requiring that they spend about 36 hours in near isolation while they wait for the results of a COVID-19 test administered when they get to campus, they’ll need to remain quarantined until after results are also available from a second round of tests.

Joshua McIntosh, vice president for campus life, said, “The arrival of students to campus from all over the country and world is a challenging and vulnerable time, and it is important that we all do our part to mitigate the risk of transmission.”

In a message to students, he said the switch to stricter plans was made because of rising transmission rates and public health guidance.

What it means is that students who arrive Thursday and Friday cannot leave campus and are required to stay in their rooms except for bathroom breaks, medical tests and to grab meals until about 9 p.m. Tuesday.

The one big exception is that they will be allowed to “spend as much time outside on campus” as they like as long as they wear a face covering, stay physically distanced and gather in groups of no more than three.

The main concern is that students who are inside stay apart from one another.

“We know this change is inconvenient, but we are doing everything we can to increase the likelihood that students will be able to begin attending classes in person on Wednesday,” McIntosh said.

McIntosh said that “as other colleges and universities have welcomed students back to campus, we have been able to learn from their experiences, including how peer colleges are seeing students test positive for COVID-19 upon their return to campus.”

“Given increased COVID transmission and the fact that most activities have moved indoors, we expect that our start this semester will be more challenging than our start this past fall,” when only a few coronavirus cases were found, he said.

Bates is testing every student on arrival with two different methods. One offers a quick, but less reliable outcome. The other is sent to the Broad Institute in Boston and usually takes about 36 hours for results to come back.

Any student testing positive in the on-the-spot method will be moved to isolation housing pending the more accurate results.

But every student, including those living off-campus, is mandated to obey rules that keep them largely in their rooms until the second round of results come back from the Broad Institute for tests taken on Sunday and Monday.

McIntosh said he expects to send students an email Tuesday evening letting them know results and freeing most to leave their rooms, though they will still be required to wear masks and respect social distancing.

The college hopes its rules keep transmission rates low.

“We look forward to welcoming you back to campus,” McIntosh told students, “and, with your cooperation, I am optimistic that we will have a successful semester.”