There are now at least four major diagnostics makers who are producing COVID-19 tests for the U.S., including Abbott ABT, -8.72%, Hologic Inc. HOLX, -2.81%, Roche Holding AG ROG, -4.98%, and Thermo Fisher Scientific Inc. TMO, -0.88%. The Centers for Disease Control and Prevention and the U.S. public health laboratories have conducted at least 37,824 tests so far, the CDC has said.