SAN FRANCISCO — A hoax? Just the flu? A serious pandemic? The conflicting messages as the coronavirus spreads across the nation leave Americans wondering what and who to believe.

In Silicon Valley, a hot spot in the outbreak, one outspoken doctor boasts that his guidance comes with no spin and no political filter, despite efforts by some in his department to tone down his messages.

“Nobody tells me what to say — nobody,” said Dr. Scott Morrow, the chief health officer for San Mateo County, which includes the headquarters of Facebook and many other big technology companies.

Dr. Morrow has made a name for himself as the medical officer who dispenses pithy, unvarnished and personalized bulletins on the outbreak as it moves through his part of the country, a departure from the sterile health warnings issued by most other health officials.