“Those are really released just as provisional, and honestly it takes several months past the end of the year for a state to finalize those numbers,” said Orion McCotter, a CDC epidemiologist.

This means that the nation’s lead agency tasked with protecting the public from serious diseases does not know the full extent of a valley fever outbreak until months after it occurred. Early detection and treatment is especially important as valley fever can spread from the lungs to other parts of the body and ultimately become fatal.

CDC officials would not address deficiencies in the reporting process, and instead referred reporters’ questions to the California Department of Public Health.

“This is just the system that we have right now, and I think lag-time questions need to go to the local and state (agencies) for what their process is, but I think this is the best system available,” Brittany Behm, a CDC spokeswoman, said before abruptly ending an interview.

The data deficiency exacerbates what researchers already describe as widespread underreporting. Experts estimate that valley fever infects more than 150,000 people across the Southwest alone, with 50,000 being sick enough to require medical attention. And yet CDC reports of people infected with the disease have never exceeded 23,000 cases nationwide.