The H5N1 bird flu appears to be stampeding through dairy farms in California, the country's largest milk producer. Over the weekend, the total number of confirmed infected cow herds stunningly doubled, going from 17 last Thursday to 34 Monday morning, according to state and federal officials.

Reports of H5N1 bird flu outbreaks at California dairy herds are continuing to rise as the nation’s largest milk producer scrambles to contain the spread. On Monday, officials reported that the number of infected dairy herds in the Central Valley had doubled over the weekend, rising from 17 to 34.

In the Central Valley, the state's Department of Food and Agriculture says 34 total dairy farms have had bird flu infections in their dairy herds

But the leap in the number of infected herds — tripling from 10 to 34 in the past week at California’s 1,000 dairies — is troubling to the state’s vibrant dairy industry, a major part of the state’s agricultural industry and the nation’s top milk producer.

The mandatory testing comes as the total number of infected herds in California has risen to 17. Nationally, officials have announced 218 outbreaks across 18 states. In the last 30 days, however, California has accounted for all but two of the latest outbreaks.

Why it matters: California now accounts for all but two of the nation’s recent H5N1 bird flu outbreaks in livestock over the past 30 days.

Authorities are still investigating how the virus slipped in from outside the state, where 237 herds in 14 states are affected.

California's dairy industry grapples with a sudden surge in H5N1 bird flu cases, raising concerns about potential human transmission.