It’s been nearly three months since the U.S. government announced an outbreak of the bird flu virus on dairy farms. The World Health Organization considers the virus a public health concern because of its potential to cause a pandemic, yet the U.S. has tested only about 45 people across the country. “We’re flying blind,” said Jennifer Nuzzo, director of the Pandemic Center at the Brown University School of Public Health. With so few tests run, she said, it’s impossible to know how many farmworkers have been infected, or how serious the disease is. A lack of testing means the country...