But even as pasteurized milk became more and more popular, ranchers and farmers struggled to eradicate brucellosis in their cattle herds, where it causes spontaneous abortions. In 1996, they started using RB51 to vaccinate against Brucella abortus, a strain that typically infects cattle. The vaccinations have been really successful: In the mid-aughts, Texas became the 50th state to be declared brucellosis-free. “Texas continues a high-level surveillance program to determine if the field strain Brucella abortus is present,” said Thomas Swafford, public information officer for the Texas Animal Health Commission in an email. “Since 2008, there has not been any field strain B. abortus detected in Texas with exception of one beef herd in a county that borders Mexico.”

At K-Bar Dairy, the infection matched the strain from the vaccine—again, that’s RB51. “Even when the vaccine is properly administered, a cow can rarely become persistently infected if the cow matures early,” Swafford says. In this case, the cows were likely vaccinated with RB51, then the strain stayed alive in their bodies. They “shed” that bacteria into the milk they produced. And since humans aren’t vaccinated against brucellosis in the way cattle are, human milk drinkers are vulnerable to getting sick from the vaccine strain meant for the cows. “We believe it is highly unusual for this vaccine strain brucella to be shedding in the milk,” Swafford says, “but that is one reason why pasteurization is important.” K-Bar Dairy did not respond to requests for comment.

Selling raw milk is legal in Texas. It’s sold directly from the farm, and it’s highly regulated through the Milk and Dairy Program at the Texas Department of State Health Services (DSHS). Raw-milk dairies are inspected twice every six months by registered sanitarians. And the milk itself is tested every six weeks. “There is regular testing done, and that is done both for milk quality—making sure it has the right fat content—and also for pathogens,” says Chris Van Deusen, director of media relations at DSHS.

But Van Deusen also says those pathogen tests aren’t designed to detect brucellosis: “It is not something that is routinely tested for.” That means even if K-Bar Dairy had tested the exact same pint of milk that wound up infecting a human, the RB51 would’ve stayed under the radar.

It appears that every entity did the responsible thing in this situation. The dairy vaccinated its cows and followed the rules. Investigators sprung into action as soon as the disease was discovered. A dizzying network of officials coordinated a rapid response (the CDC even enlisted 65 volunteers to help contact some of the affected households).

But there are still a lot of people who don’t feel sick and haven’t heard the news. Salzer says it’s possible someone could be infected and continue to feel healthy for another four months. Pasteurization is starting to look more and more delicious. Right?