America's experiment in reopening universities in an ongoing pandemic is already teetering.

The novel coronavirus is spreading at some schools so much, it's driving up infection rates for whole counties. Too few schools have containment plans that reflect the basic threats: an already high COVID case rate in the U.S., and the tendency of young adults to socialize and underestimate the consequences of carelessness.

The recipe for protecting a community from COVID-19 is no secret. Social distancing and masking are vital, and it's essential to test broadly, isolate the infected and trace their contacts. These steps don't work so well if they're done halfheartedly, however, or if an outbreak is already out of control. Many schools that have acted too slowly need to pause in-person classes and other activities and rethink their strategies.

Most colleges are broadly limiting gatherings to a certain number of people and attempting to test students and trace the contacts of those who test positive. Many schools also encourage students to use apps that will notify them if they've been near an infected person, and/or require students to certify their health status daily by filling out symptom questionnaires.

Such measures rely on broad cooperation from students, and regular testing. After all, app notifications and tracing can work only if you can find out who's infected — including people who never develop symptoms.

Testing all students every two to three days could make it possible to control outbreaks, research by A. David Paltiel of Yale has shown. Symptom-based screening alone is not enough, Paltiel found; it misses too many cases. Yet many schools began this academic year doing little more than that.

The University of Georgia, where surveillance tests have been limited and optional, reported more than 800 new cases of COVID-19 during the last week of August. The University of South Carolina already has more than 1,400 active cases and a test-positivity rate in the double digits — and was recently forced to pause expanded saliva testing after a lab staffer fell ill. The University of Iowa, which neglected to test students when they arrived and is relying on them to self-report positive tests and exposure, has had more than 1,500 cases since Aug. 18. Dozens of other schools have followed similar strategies, and have experienced early outbreaks.

On the other hand, some colleges that have practiced careful surveillance are largely controlling the disease. Boston University, where all undergraduates get tested twice a week, has only 21 active cases of COVID-19. It has the advantage of being in a state with a declining case count. Duke, in North Carolina, is not so lucky, but it has kept its number of confirmed positive cases to 52 so far — by conducting pooled tests and quarantining contacts of possibly infected people as they wait for results. Neighboring University of North Carolina and North Carolina State failed to be as careful at the start of the year; their students have had to be sent home to study remotely.

Mass testing is not a panacea. Consider the University of Illinois at Champaign-Urbana, which has what may be the most ambitious testing program in the U.S. Using an internally developed saliva test, the school is screening all students twice a week, which amounts to about 10,000 tests a day. But having experienced a surge of infections, it is now asking undergraduates to stay home for two weeks unless they're attending classes or engaging in other essential activities. University leaders had anticipated some student partying but had hoped their testing model would contain any outbreaks. They didn't foresee that too many students would ignore contact tracers and attend parties after testing positive.

If UICU, whose average positive test rate over the past seven days has been a very low 1.2 percent, needs a two-week slowdown, other schools with minimal or no surveillance testing have to take more drastic measures, including stopping all in-person instruction, until they see a steady decline in cases — even if that takes a month or more.

Colleges that don't do enough testing almost certainly undercount their COVID-19 cases. As more and more schools learn that the hard way, they should waste no time in setting up adequate screening programs. Broad testing, student cooperation and low case counts need to be the goals for all colleges. Anything less puts their students and their wider communities at risk.

Max Nisen is a Bloomberg columnist covering biotech, pharma and health care.